Over the last 2 weeks, I have spent several hours debugging a magneto ignition system for a 125 Bronco and finally got it to work. The system is the same setup as is used on the early 250 scramblers and early Mark 3/Mach 1's, so I thought there would be interest and also maybe someone out there can help with the additional questions I have.
The first thing I did was to get out an ohm meter and check the High Voltage (HV) coil, per Jim Frazen's excellent diagram. HV coil was ok. I also checked the plug - plug is ok. That leaves 3 components, condenser, points and charging coil. I used a cheap analog meter to check the condenser, which showed to be open and bad. After I got a new one (domiracer) I checked it with a better digital meter and could see the resistence building in the new condenser as the condenser was taking the charge. Then for grins, I checked the old condenser with the same meter, and it also worked properly (shows resistence of 1-2 M ohms, climbing to 4-5 M ohms). Ok, so I wasted $25. I must have check the points 10 time for continuity, and points seemed fine. SO, I proceeded to replace the charging coil, $45 at domiracer. The old coil showed about 1 ohm resistence and the new coil showed about 2.5 ohm resistence. Continuity check was ok on both. I replaced the coil with the new one and while doing so took out the points and noticed that they were carbon covered, so used an emery board to clen the surfaces. When, I put it all back together, I got spark !
So, while I am not going to change anything at this point, I was not convinced the charging coil was bad and suspect the points, although they passed a continuity check, may have been dirty enough to not ground the condenser when closed. I also do not know if there is a way to test the coils ?
Got any ideas ?
Tony
Magneto ignition system diagnosis
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ajleone
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MotoMike
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Re: Magneto ignition system diagnosis
As I study these sysems, they don't really seem like magneto ignitions to me. At least not like the ones I recall on my Grand Dad's 10-20 McCormick Deering. 
In truth you don't need a condenser in there to make your ignition work. It serves as a breaker points preservation device. The condenser is a capacitor that charges up to give less difference of potential between the two contacts of the points when they open.
One of the reasons coils work for ignition is that when you remove power to them, the collapsing field generates a much larger voltage than was applied to them initially. Depending on the system this combined with the step up windings in the coil can and does result in many tens of thousands of volts. (theoretically much more) This large voltage (i.e. difference in potential) in the secondary is what causes the spark to reliably jump across the plug. To a lesser degree this phenomenon exists in the primary ( the circuit where the points reside) and the job of the condenser is to charge to some portion of this large voltage value. Then when the points open, there is less difference of potential between them and less arc drawn across them. Ideally you want the arc across the points eliminated because it is hot and will eat away at the points face surface. Actually transfer material from one point face to the other. A shorted condenser will render your system inoperable, but an open one will allow your system to work while burning your points more quickly.
I've found that just taking these things apart that might have been sitting for decades and cleaning and and reinstalling may have eliminated a bad connection and rendered the system operable again. especially if the system was functional when put into storage.
regards,
Mike
In truth you don't need a condenser in there to make your ignition work. It serves as a breaker points preservation device. The condenser is a capacitor that charges up to give less difference of potential between the two contacts of the points when they open.
One of the reasons coils work for ignition is that when you remove power to them, the collapsing field generates a much larger voltage than was applied to them initially. Depending on the system this combined with the step up windings in the coil can and does result in many tens of thousands of volts. (theoretically much more) This large voltage (i.e. difference in potential) in the secondary is what causes the spark to reliably jump across the plug. To a lesser degree this phenomenon exists in the primary ( the circuit where the points reside) and the job of the condenser is to charge to some portion of this large voltage value. Then when the points open, there is less difference of potential between them and less arc drawn across them. Ideally you want the arc across the points eliminated because it is hot and will eat away at the points face surface. Actually transfer material from one point face to the other. A shorted condenser will render your system inoperable, but an open one will allow your system to work while burning your points more quickly.
I've found that just taking these things apart that might have been sitting for decades and cleaning and and reinstalling may have eliminated a bad connection and rendered the system operable again. especially if the system was functional when put into storage.
regards,
Mike
Last edited by MotoMike on Mon Oct 11, 2010 6:35 pm, edited 1 time in total.
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DewCatTea-Bob
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Re: Magneto ignition system diagnosis
" Over the last 2 weeks, I have spent several hours debugging a magneto ignition system for a 125 Bronco and finally got it to work. "
____ Too bad that you didn't ask for guidance sooner then, Tony ! _ As I could've saved you somewhat.
" The system is the same setup as is used on the early 250 scramblers and early Mark 3/Mach 1's, "
____ I have some corrections to add to this...
The Bronco set-up is not exactly the same, however it is indeed more like a true-magneto set-up than that used on some narrow-case 250-models.
And the Mach-I, (unlike the Mark-3), used a battery-powered ignition set-up.
" I used a cheap analog meter to check the condenser, which showed to be open and bad. "
____ Actually, a good condenser/capacitor should indeed measure "open" ! _ To check one, you should first make sure to discharge it by contacting it to itself, then when you use an ohm-meter to check it, it should at first show as a 'short' and then the meter's readout should soon change towards showing the unit as 'open' !
" After I got a new one (domiracer) I checked it with a better digital meter and could see the resistence building in the new condenser as the condenser was taking the charge. "
____ Right, that's as it should be !
Perhaps you just didn't happen to take-note of the charging-up process with your other meter.
" I checked the old condenser with the same meter, and it also worked properly
Ok, so I wasted $25.
____ Wow, I guess you did. _ Condensers seldom ho bad !
If you had also measured the new-condenser with the first-meter, you no doubt would've then seen it measure-out the same as the old-condenser did, as well.
" I must have check the points 10 time for continuity, and points seemed fine. "
____ Then it's my guess that you must've used a tester other than an ohm-meter, cuz it's possible for the contact-points to pass enough juice to satisfy a low-wattage tester, yet not enough juice to fully power-up an ign.coil !
" I proceeded to replace the charging coil,
The old coil showed about 1 ohm resistence and the new coil showed about 2.5 ohm resistence. Continuity check was ok on both. "
____ Of course the continuity-check would be satisfied in either case, but you can see where the ohm-meter indeed found a slight difference, (when you tried both checking-devices for this particular part, [but apparently not for the points] ) !
That the new power-coil had a higher ohm-reading (on the same meter), indicates that it may be that some of the windings of the old coil have shorted together through their separating-insulation.
" I replaced the coil with the new one and while doing so took out the points and noticed that they were carbon covered, so used an emery board to clen the surfaces. When, I put it all back together, I got spark ! "
____ It's too bad that you didn't try the clean-up of the points first, so that you'd then know for sure which issue was the actual source of your problem. _ As either could have cut sufficient power for powering-up the ign.coil enough to make a spark.
Also, (without knowing if one or the other was the actual-cause all by itself), it could be possible that both deficiencies worked together just enough each, to then cause your ignition-problem. _ And you probably hope that that was the case, (so that you won't have purchased the new power-coil for no good reason).
" I was not convinced the charging coil was bad and suspect the points
may have been dirty enough to not ground the condenser when closed. "
____ The purpose of the condenser does not require it to be grounded by the points in order to make a spark,, rather, it's purpose is to absorb current-pressure that would otherwise wish to arc-jump the points-gap and thus tend to tear-up the flat-surfaces of the contacts.
The spark itself would be a bit more intense without a condenser (since it tends to soften the charge of the power-blow to the ign.coil, when the points open), at the expense of contact-life of course.
DUCATIly,
-Bob
____ Too bad that you didn't ask for guidance sooner then, Tony ! _ As I could've saved you somewhat.
" The system is the same setup as is used on the early 250 scramblers and early Mark 3/Mach 1's, "
____ I have some corrections to add to this...
The Bronco set-up is not exactly the same, however it is indeed more like a true-magneto set-up than that used on some narrow-case 250-models.
And the Mach-I, (unlike the Mark-3), used a battery-powered ignition set-up.
" I used a cheap analog meter to check the condenser, which showed to be open and bad. "
____ Actually, a good condenser/capacitor should indeed measure "open" ! _ To check one, you should first make sure to discharge it by contacting it to itself, then when you use an ohm-meter to check it, it should at first show as a 'short' and then the meter's readout should soon change towards showing the unit as 'open' !
" After I got a new one (domiracer) I checked it with a better digital meter and could see the resistence building in the new condenser as the condenser was taking the charge. "
____ Right, that's as it should be !
Perhaps you just didn't happen to take-note of the charging-up process with your other meter.
" I checked the old condenser with the same meter, and it also worked properly
Ok, so I wasted $25.
____ Wow, I guess you did. _ Condensers seldom ho bad !
If you had also measured the new-condenser with the first-meter, you no doubt would've then seen it measure-out the same as the old-condenser did, as well.
" I must have check the points 10 time for continuity, and points seemed fine. "
____ Then it's my guess that you must've used a tester other than an ohm-meter, cuz it's possible for the contact-points to pass enough juice to satisfy a low-wattage tester, yet not enough juice to fully power-up an ign.coil !
" I proceeded to replace the charging coil,
The old coil showed about 1 ohm resistence and the new coil showed about 2.5 ohm resistence. Continuity check was ok on both. "
____ Of course the continuity-check would be satisfied in either case, but you can see where the ohm-meter indeed found a slight difference, (when you tried both checking-devices for this particular part, [but apparently not for the points] ) !
That the new power-coil had a higher ohm-reading (on the same meter), indicates that it may be that some of the windings of the old coil have shorted together through their separating-insulation.
" I replaced the coil with the new one and while doing so took out the points and noticed that they were carbon covered, so used an emery board to clen the surfaces. When, I put it all back together, I got spark ! "
____ It's too bad that you didn't try the clean-up of the points first, so that you'd then know for sure which issue was the actual source of your problem. _ As either could have cut sufficient power for powering-up the ign.coil enough to make a spark.
Also, (without knowing if one or the other was the actual-cause all by itself), it could be possible that both deficiencies worked together just enough each, to then cause your ignition-problem. _ And you probably hope that that was the case, (so that you won't have purchased the new power-coil for no good reason).
" I was not convinced the charging coil was bad and suspect the points
may have been dirty enough to not ground the condenser when closed. "
____ The purpose of the condenser does not require it to be grounded by the points in order to make a spark,, rather, it's purpose is to absorb current-pressure that would otherwise wish to arc-jump the points-gap and thus tend to tear-up the flat-surfaces of the contacts.
The spark itself would be a bit more intense without a condenser (since it tends to soften the charge of the power-blow to the ign.coil, when the points open), at the expense of contact-life of course.
DUCATIly,
-Bob
PLEASE NOTE... If this-post is not-yet signed-off with '-Bob', then I'm still in the process of completing it,, and if not also included with 'DCT' near bottom as well, then I may edit this post's wording at a later time. - Dct.Bob
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DewCatTea-Bob
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Re: Magneto ignition system diagnosis
" As I study these sysems, they don't really seem like magneto ignitions to me. "
____ Well that's cuz they're really NOT !
Here's the low-down on why so many still think that some Ducati-models were made with "magnetos" located in place of the actual alternator.....
__ First I must admit that even I always used to use the term 'magneto' (instead of 'alternator') back in the '60s, (before I was rightfully educated in Tech.school about all things to do with electrics), whenever then referring to the magneto-TYPE of ignition-systems as once used on some DUKE-models (& many other motor-bikes too).
The reason that I myself ever referred to those battery-less ignition-systems as "magnetos", was only cuz everyone else did. _ It's the same kind of word-misusage as using the word 'auto' to refer to any car... (Cars were not called 'automobiles' until after they came to include automatic-transmissions, so then logically, cars with auto-transmissions became known as auto-mobiles -(a big sales-gimmick for enticing the ladies!), and so then later, it came to a point where any car could be referred to as an "auto", even still (illogically) if it had a std.transmission !
Well it's much the same sort of thing with the illogical use of the word 'magneto'... A 'mag' -(as they may say), is a single-device which does all three steps in just one unit... It produces it's very-own power-juice (for ignition only!), and, it contains it's own contact-points & ign.timing set-up, and, it includes it's own High-Tension (step-up)- coil, for producing high-voltage ign.sparking-juice to the plug.
__ On the OHC-DUKEs, all these three separate steps are located in completely separate & isolated places on the motorcycle ! _ So it's a laugh when an uninformed-soul is asked "Where's the magneto on this Ducati ?", and the poor-guy then points at where it's alternator is located, (and the inquisitor then wonders where the spark-plug's wire-lead comes-out of there at, [and perhaps they both then figure that the black-cable coming-out from near the kick-starter, must be it] !). - (Bet I'm not the only one who's heard of such a story!)
Anyhow, it seems the reason that the 4-pole alternator is the part which gets the rap as being the 'magneto', is because it's the main-root power-maker for the magneto-like set-up that some Duc.Singles employ.
However in the case of the Bronco, only the HT-ign.coil is separate from the other two parts of it's magneto-type ignition set-up ! _ Thus that's why I've stated that it's more like a real/true magneto.
" The condenser is a capacitor that charges up to give less difference of potential between the two contacts of the points when they open. "
____ I believe that you'd agree that it would be more sensibly worded to state that the condenser initially acts as a 'short-circuit' so as to save the points from current-pressure/momentum as they first open, (and also of course conveniently act less & less like a short-circuit [as well as more & more like an open-circuit] as it charges,, and as the points open further & further apart), rather than (as you had put it)- "charges up",, so as to provide a lesser difference of potential between the contacts. _ Otherwise, a reader is likely lead to think that the condenser needs to become charged-up to accomplish some (actually unneeded) task with it's built-up charge of juice, afterwords,, when in fact it's job has already been done at the moment it was acting as a short.
" One of the reasons coils work for ignition is that when you remove power to them, the collapsing field generates a much larger voltage than was applied to them initially. "
____ Yeah, that's somewhat true but, ONLY for the battery/DC-powered type ign.set-ups, and thus may be confusing to be mentioned here within THIS thread concerning the magneto-type ignition-coils (which make THEIR spark when the 'EXPANDING-flux' [not collapsing-flux!] is first generated !).
" To a lesser degree this phenomenon exists in the primary ( the circuit where the points reside) and the job of the condenser is to charge to some portion of this large voltage value. Then when the points open, there is less difference of potential between them and less arc drawn across them. "
____ I'm really sorry to inform you here Mike, but you really need to think-over what you've written before you go-ahead & post it...
First, you seem to still be in reference here, to just the battery-type ign.system,, and second, what you've written (directly above) seems to make fair sense but only providing that IF the charged condenser is connected to the (separated) contact-point that's opposite the other contact-point which is always still left connected to the ign.coil, (so that the potential between the two points would then be lessened, as you say).
But actually Mike, the condenser & the ign.coil -(which you say highly charges-up the condenser, so it can do it's job), are BOTH at all times left connected to the very-same contact-point ! - (Thus never getting any chance to help balance the potential between the two points). _ So then it would seem that your theory for the purpose of the charging-up of the condenser, would then ACTUALLY have both the ign.coil AND the condenser working together to even further UN-balance the potential-difference between the hot-point & the grounded-point, rather than (as you seem to have indicated), help balance it out, between the two points !
__ Put your thinking-cap on and determine for us both that I'm not only correct with what I've claimed but also that I have understood that which you were trying to suppose. _ (It's sort of doubtful that anyone else here besides yourself & I have gotten any firm-grasp of your working-theory that it seems you were meaning to convey.)
____ Here's what's really going-on with the battery-type ign.system...
__ The contact-point's close and then the battery-supplied DC-current goes through the points to also pass-through the ign.coil's windings so as to create a field of magnetic-flux around the coil, (which build's up it's EXPANDING flux-field too slowly to produce a notable spark). _ Then when the points open, the flux-field then (more rapidly) collapses, and just as the DC-current produced a correspondingly-sized flux-field around the coil, that collapsing flux-field thus creates a correspondingly identical DC-current right-back into the same primary-windings, just like the primary-current that was flowing before the points opened !
But what's really cool about this is that the same collapsing flux-field can be taken advantage of to also induce current within the (otherwise dead) high-ratio secondary-windings as well, thus providing a High-Tension version of the primary's current ! - (How conveniently neat is that !?) _ And since the secondary-winding-set has far more (and thinner) windings (than the primary), it thus creates higher voltage, (but less amperage, [to equal the same amount of wattage]), which is of a high enough potential to jump the spark-gap.
__ Now getting back to the primary-winding and the reason for the condenser...
The collapsing flux-field cannot be stopped from doing so, and so it's going to create the exact same electron-flow which had created it, no matter what !!! _ So when the points open, that induced flow of electrons is in no way going to stop & say: "Okay we'll just wait here until you close again",, there's just no way to stop the coil's induced electron-flow before it's self-satisfied, it just has got to go somewhere that will complete it's urge to flow!! _ And so it's batch of electrons will easily jump any gap to get themselves delivered where-ever they need to go in order to maintain the same electron-flow until it's satisfied ! _ And that means it will have to jump the points-gap no matter how big it is, cuz there's just no stopping it & it just won't take No for an answer, as it absolutely must finish itself what ever way possible !
And that's where the condenser comes into play, as it will temporarily absorb the batch of electrons so that they won't feel the need to create the voltage needed to jump the gap and tend to burn the contact-points in the process.
And the system will only leave the condenser charged to just the same voltage as that of the battery, (until the points again discharge the condenser to ground).
And there you have it !
Dukaddy-DUKEs,
-Bob
____ Well that's cuz they're really NOT !
Here's the low-down on why so many still think that some Ducati-models were made with "magnetos" located in place of the actual alternator.....
__ First I must admit that even I always used to use the term 'magneto' (instead of 'alternator') back in the '60s, (before I was rightfully educated in Tech.school about all things to do with electrics), whenever then referring to the magneto-TYPE of ignition-systems as once used on some DUKE-models (& many other motor-bikes too).
The reason that I myself ever referred to those battery-less ignition-systems as "magnetos", was only cuz everyone else did. _ It's the same kind of word-misusage as using the word 'auto' to refer to any car... (Cars were not called 'automobiles' until after they came to include automatic-transmissions, so then logically, cars with auto-transmissions became known as auto-mobiles -(a big sales-gimmick for enticing the ladies!), and so then later, it came to a point where any car could be referred to as an "auto", even still (illogically) if it had a std.transmission !
Well it's much the same sort of thing with the illogical use of the word 'magneto'... A 'mag' -(as they may say), is a single-device which does all three steps in just one unit... It produces it's very-own power-juice (for ignition only!), and, it contains it's own contact-points & ign.timing set-up, and, it includes it's own High-Tension (step-up)- coil, for producing high-voltage ign.sparking-juice to the plug.
__ On the OHC-DUKEs, all these three separate steps are located in completely separate & isolated places on the motorcycle ! _ So it's a laugh when an uninformed-soul is asked "Where's the magneto on this Ducati ?", and the poor-guy then points at where it's alternator is located, (and the inquisitor then wonders where the spark-plug's wire-lead comes-out of there at, [and perhaps they both then figure that the black-cable coming-out from near the kick-starter, must be it] !). - (Bet I'm not the only one who's heard of such a story!)
Anyhow, it seems the reason that the 4-pole alternator is the part which gets the rap as being the 'magneto', is because it's the main-root power-maker for the magneto-like set-up that some Duc.Singles employ.
However in the case of the Bronco, only the HT-ign.coil is separate from the other two parts of it's magneto-type ignition set-up ! _ Thus that's why I've stated that it's more like a real/true magneto.
" The condenser is a capacitor that charges up to give less difference of potential between the two contacts of the points when they open. "
____ I believe that you'd agree that it would be more sensibly worded to state that the condenser initially acts as a 'short-circuit' so as to save the points from current-pressure/momentum as they first open, (and also of course conveniently act less & less like a short-circuit [as well as more & more like an open-circuit] as it charges,, and as the points open further & further apart), rather than (as you had put it)- "charges up",, so as to provide a lesser difference of potential between the contacts. _ Otherwise, a reader is likely lead to think that the condenser needs to become charged-up to accomplish some (actually unneeded) task with it's built-up charge of juice, afterwords,, when in fact it's job has already been done at the moment it was acting as a short.
" One of the reasons coils work for ignition is that when you remove power to them, the collapsing field generates a much larger voltage than was applied to them initially. "
____ Yeah, that's somewhat true but, ONLY for the battery/DC-powered type ign.set-ups, and thus may be confusing to be mentioned here within THIS thread concerning the magneto-type ignition-coils (which make THEIR spark when the 'EXPANDING-flux' [not collapsing-flux!] is first generated !).
" To a lesser degree this phenomenon exists in the primary ( the circuit where the points reside) and the job of the condenser is to charge to some portion of this large voltage value. Then when the points open, there is less difference of potential between them and less arc drawn across them. "
____ I'm really sorry to inform you here Mike, but you really need to think-over what you've written before you go-ahead & post it...
First, you seem to still be in reference here, to just the battery-type ign.system,, and second, what you've written (directly above) seems to make fair sense but only providing that IF the charged condenser is connected to the (separated) contact-point that's opposite the other contact-point which is always still left connected to the ign.coil, (so that the potential between the two points would then be lessened, as you say).
But actually Mike, the condenser & the ign.coil -(which you say highly charges-up the condenser, so it can do it's job), are BOTH at all times left connected to the very-same contact-point ! - (Thus never getting any chance to help balance the potential between the two points). _ So then it would seem that your theory for the purpose of the charging-up of the condenser, would then ACTUALLY have both the ign.coil AND the condenser working together to even further UN-balance the potential-difference between the hot-point & the grounded-point, rather than (as you seem to have indicated), help balance it out, between the two points !
__ Put your thinking-cap on and determine for us both that I'm not only correct with what I've claimed but also that I have understood that which you were trying to suppose. _ (It's sort of doubtful that anyone else here besides yourself & I have gotten any firm-grasp of your working-theory that it seems you were meaning to convey.)
____ Here's what's really going-on with the battery-type ign.system...
__ The contact-point's close and then the battery-supplied DC-current goes through the points to also pass-through the ign.coil's windings so as to create a field of magnetic-flux around the coil, (which build's up it's EXPANDING flux-field too slowly to produce a notable spark). _ Then when the points open, the flux-field then (more rapidly) collapses, and just as the DC-current produced a correspondingly-sized flux-field around the coil, that collapsing flux-field thus creates a correspondingly identical DC-current right-back into the same primary-windings, just like the primary-current that was flowing before the points opened !
But what's really cool about this is that the same collapsing flux-field can be taken advantage of to also induce current within the (otherwise dead) high-ratio secondary-windings as well, thus providing a High-Tension version of the primary's current ! - (How conveniently neat is that !?) _ And since the secondary-winding-set has far more (and thinner) windings (than the primary), it thus creates higher voltage, (but less amperage, [to equal the same amount of wattage]), which is of a high enough potential to jump the spark-gap.
__ Now getting back to the primary-winding and the reason for the condenser...
The collapsing flux-field cannot be stopped from doing so, and so it's going to create the exact same electron-flow which had created it, no matter what !!! _ So when the points open, that induced flow of electrons is in no way going to stop & say: "Okay we'll just wait here until you close again",, there's just no way to stop the coil's induced electron-flow before it's self-satisfied, it just has got to go somewhere that will complete it's urge to flow!! _ And so it's batch of electrons will easily jump any gap to get themselves delivered where-ever they need to go in order to maintain the same electron-flow until it's satisfied ! _ And that means it will have to jump the points-gap no matter how big it is, cuz there's just no stopping it & it just won't take No for an answer, as it absolutely must finish itself what ever way possible !
And that's where the condenser comes into play, as it will temporarily absorb the batch of electrons so that they won't feel the need to create the voltage needed to jump the gap and tend to burn the contact-points in the process.
And the system will only leave the condenser charged to just the same voltage as that of the battery, (until the points again discharge the condenser to ground).
And there you have it !
Dukaddy-DUKEs,
-Bob
PLEASE NOTE... If this-post is not-yet signed-off with '-Bob', then I'm still in the process of completing it,, and if not also included with 'DCT' near bottom as well, then I may edit this post's wording at a later time. - Dct.Bob
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MotoMike
- Posts: 487
- Joined: Wed Aug 04, 2010 3:40 am
Re: Magneto ignition system diagnosis
Thanks again Bob. Look at it this way, if you didn’t have to keep me in line, there’d be a lot less discussion going on here lately. Also, this is just the kind of activity I need to stave off mental atropy
And you are right; I got it wrong as it pertains to the AC ignition system. I think I’m OK on the battery ignition though. But since I was talking battery, I lent an air of confusion to the thread.
For those who don’t want to read this overly long post: I still stand by my comment though, that an open condenser will not keep your ignition from operating be it battery or ac magneto. A shorted one will stop you dead in your tracks.
I need to study these schematics a bit more and as you suggest, do that before posting. At this point though, I think I should leave that previous post unaltered,(even though it’s a little embarrassing for me) as without it your post looses context and meaning for those who want to see what you and I are talking about.
I have for many years noted that people find different ways to say the same thing. And I think that is the case in discussing the condenser. My discussion of the topic comes from a military technician background (something I’ve been away from for 15 years) more than from a mechanics background. Each field has a different way of saying things. Voltage is a difference of potential. Current is electron flow caused by a diffenece in potential. A condenser is a capacitor. A discharged capacitor has no difference of potential across the plates plate. A charged capacitor has a difference of potential across the plates.
So as you say, the capacitor/condenser does act as a short circuit initially. And you say it absorbs the current so that it is less inclined to jump the gap the points create. We are down to semantics I think. And we may be beating a dead horse, but I started this, so on the off chance there is anyone who cares to see what we are talking about, I’ll go on. When you say it absorbs current initially, I think that is true, and a way of saying the capacitor is charging. Initially discharged ie ground on both sides, then charging as the non grounded side rises while the grounded side stays at ground potential. If it didn’t do this, the non grounded side of the points would see the full potential, probably at least a few hundred volts at the instant they open. With the capacitor there, at the instant it opens, you should see ground potential on the non grounded point face, then over an unknown period of time the cap will charge attempting to reach the full potential of what ever voltage is applied to the non grounded side. In truth we are seeing a dynamic event here and as the cap is charging, the voltage supplied on the non grounded side is changing. So we don’t know what values are actually being felt there, but it is safe to say that initially, the cap causes there to be less difference of potential across the point faces and therefore reduces the arc drawn across them and extends the point life because of it.
You are right in stating that I was thinking of the circuit working as a battery supplied system. The non rectified AC non battery system is a different animal entirely. A closer look at the circuit and I see that it is not working at all like the battery ignition. Charging or magnetizing current only goes through the coil primary when the points are open, just the opposite of the battery ignition.
As mentioned before a cap initially acts as a short until it charges up. It should be noted that an inductor initially acts as an open until it “charges” and then acts as a short (minus resistance in the windings). The time it takes to do this is known as 5 time constants. These circumstances exist in a pure DC circuit only. And the actual length of each time constant is determined by the inductance, capacitance and resistance in these circuits.
In an AC circuit they will, owed to the constantly changing supply be in some state of charge/discharge as they follow the input. That is where it gets tricky, because the designer can choose the values of capacitance, resistance and inductance to make the time relationships very short or very long or somewhere in between. To further complicate this there is a reactive component where capacitors and inductors oppose current based on the frequency of the AC supplied. And the cap and inductors phase relationship (current and voltage) will be opposite one another.
I only mention these relationships to account for why I have not fully figured out what is going on in the non battery ignitions.
You mention that the spark is produced when the field is being built. Thanks for that, as in looking at the circuit, I could envision a stronger spark being built when you close the points and create a very low resistance path for the current to go to and create potentially a more rapid collapse of the field. Perhaps a second spark is produced and as Jim has pointed out to me, goes to no good effect as the piston is past the power stroke.
These discussions are best done while sitting side by side with the schematic in front of us. That is why I try to take pains to describe the location I’m speaking of. (ie ground side of the points etc) That may be why I'm having trouble following all of what you are saying towards the end of the discussion.
I think you are generally right about what is going on in the battery points ignition. But you don’t acknowledge that the collapsing field causes a much higher voltage to be induced in the secondary than the turns ratio alone would account for. I have talked to a lot of people about this and never really got a satisfactory answer. But it is governed by Faradays law which states that the amount of voltage induced in an inductor is dependant on the amount of flux, the number of turns, and the time rate of cutting.
So in an ignition coil, more current in the primary will create a more strong or dense magnetic field, and as you say when it collapses it returns that current. In the secondary this collapse creates induced voltage, each turn adds to the voltage, so this is taking advantage of the transformer step up to get a much bigger voltage across the secondary coil than the primary. Fields collapse usually faster than they are built. So we add greatly to the secondary output if we collapse the field more quickly which causes the lines of flux to cut the turns faster and therefore creating much bigger voltages. Sometimes many times bigger. As you say with the increased voltage you have a corresponding decrease in current. But in this application current is not critical because you just need to create a big enough voltage or difference in potential to cause the electrons to reliably jump the gap between the plug electrodes. The hot plasma of the spark touches off the charge in the combustion chamber.
Kind of an aside but something else we did not mention is that once a spark is initiated, the path the spark is following is essentially a short circuit through the plasma and the majority of the current will go that way. It will continue to spark as the field collapses until it reaches a point it can’t sustain itself.
Also as an aside, the condenser is not totally effective in its job. I think that at the instance the points open, it bleeds off a lot of current, but because it is charging it begins to oppose current flow as it goes towards acting like an open, the path across the points becomes the lower impedance option and some spark does jump across them. Optimally, the voltage will have dropped enough by that time to lessen the damage to the points.
And so it goes.
Thank’s again
Mike
And you are right; I got it wrong as it pertains to the AC ignition system. I think I’m OK on the battery ignition though. But since I was talking battery, I lent an air of confusion to the thread.
For those who don’t want to read this overly long post: I still stand by my comment though, that an open condenser will not keep your ignition from operating be it battery or ac magneto. A shorted one will stop you dead in your tracks.
I need to study these schematics a bit more and as you suggest, do that before posting. At this point though, I think I should leave that previous post unaltered,(even though it’s a little embarrassing for me) as without it your post looses context and meaning for those who want to see what you and I are talking about.
I have for many years noted that people find different ways to say the same thing. And I think that is the case in discussing the condenser. My discussion of the topic comes from a military technician background (something I’ve been away from for 15 years) more than from a mechanics background. Each field has a different way of saying things. Voltage is a difference of potential. Current is electron flow caused by a diffenece in potential. A condenser is a capacitor. A discharged capacitor has no difference of potential across the plates plate. A charged capacitor has a difference of potential across the plates.
So as you say, the capacitor/condenser does act as a short circuit initially. And you say it absorbs the current so that it is less inclined to jump the gap the points create. We are down to semantics I think. And we may be beating a dead horse, but I started this, so on the off chance there is anyone who cares to see what we are talking about, I’ll go on. When you say it absorbs current initially, I think that is true, and a way of saying the capacitor is charging. Initially discharged ie ground on both sides, then charging as the non grounded side rises while the grounded side stays at ground potential. If it didn’t do this, the non grounded side of the points would see the full potential, probably at least a few hundred volts at the instant they open. With the capacitor there, at the instant it opens, you should see ground potential on the non grounded point face, then over an unknown period of time the cap will charge attempting to reach the full potential of what ever voltage is applied to the non grounded side. In truth we are seeing a dynamic event here and as the cap is charging, the voltage supplied on the non grounded side is changing. So we don’t know what values are actually being felt there, but it is safe to say that initially, the cap causes there to be less difference of potential across the point faces and therefore reduces the arc drawn across them and extends the point life because of it.
You are right in stating that I was thinking of the circuit working as a battery supplied system. The non rectified AC non battery system is a different animal entirely. A closer look at the circuit and I see that it is not working at all like the battery ignition. Charging or magnetizing current only goes through the coil primary when the points are open, just the opposite of the battery ignition.
As mentioned before a cap initially acts as a short until it charges up. It should be noted that an inductor initially acts as an open until it “charges” and then acts as a short (minus resistance in the windings). The time it takes to do this is known as 5 time constants. These circumstances exist in a pure DC circuit only. And the actual length of each time constant is determined by the inductance, capacitance and resistance in these circuits.
In an AC circuit they will, owed to the constantly changing supply be in some state of charge/discharge as they follow the input. That is where it gets tricky, because the designer can choose the values of capacitance, resistance and inductance to make the time relationships very short or very long or somewhere in between. To further complicate this there is a reactive component where capacitors and inductors oppose current based on the frequency of the AC supplied. And the cap and inductors phase relationship (current and voltage) will be opposite one another.
I only mention these relationships to account for why I have not fully figured out what is going on in the non battery ignitions.
You mention that the spark is produced when the field is being built. Thanks for that, as in looking at the circuit, I could envision a stronger spark being built when you close the points and create a very low resistance path for the current to go to and create potentially a more rapid collapse of the field. Perhaps a second spark is produced and as Jim has pointed out to me, goes to no good effect as the piston is past the power stroke.
These discussions are best done while sitting side by side with the schematic in front of us. That is why I try to take pains to describe the location I’m speaking of. (ie ground side of the points etc) That may be why I'm having trouble following all of what you are saying towards the end of the discussion.
I think you are generally right about what is going on in the battery points ignition. But you don’t acknowledge that the collapsing field causes a much higher voltage to be induced in the secondary than the turns ratio alone would account for. I have talked to a lot of people about this and never really got a satisfactory answer. But it is governed by Faradays law which states that the amount of voltage induced in an inductor is dependant on the amount of flux, the number of turns, and the time rate of cutting.
So in an ignition coil, more current in the primary will create a more strong or dense magnetic field, and as you say when it collapses it returns that current. In the secondary this collapse creates induced voltage, each turn adds to the voltage, so this is taking advantage of the transformer step up to get a much bigger voltage across the secondary coil than the primary. Fields collapse usually faster than they are built. So we add greatly to the secondary output if we collapse the field more quickly which causes the lines of flux to cut the turns faster and therefore creating much bigger voltages. Sometimes many times bigger. As you say with the increased voltage you have a corresponding decrease in current. But in this application current is not critical because you just need to create a big enough voltage or difference in potential to cause the electrons to reliably jump the gap between the plug electrodes. The hot plasma of the spark touches off the charge in the combustion chamber.
Kind of an aside but something else we did not mention is that once a spark is initiated, the path the spark is following is essentially a short circuit through the plasma and the majority of the current will go that way. It will continue to spark as the field collapses until it reaches a point it can’t sustain itself.
Also as an aside, the condenser is not totally effective in its job. I think that at the instance the points open, it bleeds off a lot of current, but because it is charging it begins to oppose current flow as it goes towards acting like an open, the path across the points becomes the lower impedance option and some spark does jump across them. Optimally, the voltage will have dropped enough by that time to lessen the damage to the points.
And so it goes.
Thank’s again
Mike
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DewCatTea-Bob
- Posts: 2897
- Joined: Sun Nov 01, 2009 10:53 am
- Location: Near SE side of Lake Michigan
Suggestion For Handling of Extended Postings
WOW, I think most all would agree that we should try to make our posts shorter so that they are then more apt to be dived-into.
So I suggest that we break-up such long postings by separating their various sub-topics into separate postings, and also be sure to reset the topic-title to match the main subtopic of it's post.
It's going to take me a good time to go-through & sort-out all of that last post-wording, but I'm still looking-forward to getting through it all, within the day or so.
Stay-Tuned,
-Bob
So I suggest that we break-up such long postings by separating their various sub-topics into separate postings, and also be sure to reset the topic-title to match the main subtopic of it's post.
It's going to take me a good time to go-through & sort-out all of that last post-wording, but I'm still looking-forward to getting through it all, within the day or so.
Stay-Tuned,
-Bob
PLEASE NOTE... If this-post is not-yet signed-off with '-Bob', then I'm still in the process of completing it,, and if not also included with 'DCT' near bottom as well, then I may edit this post's wording at a later time. - Dct.Bob
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DewCatTea-Bob
- Posts: 2897
- Joined: Sun Nov 01, 2009 10:53 am
- Location: Near SE side of Lake Michigan
Re: Condenser / Ign.system Speculation
" Look at it this way, if you didn’t have to keep me in line, there’d be a lot less discussion going on here lately. Also, this is just the kind of activity I need to stave off mental atropy "
____ Well that's exactly the very same way I've already been looking at posting most of my posts here at this w.site, Mike ! _ If I hadn't already felt that way, I wouldn't have bothered with my extended response to your previous-post.
Glad that you seem to agree with my inclination !
" And you are right; I got it wrong as it pertains to the AC ignition system. "
____ We'll no doubt get further into that odd-working ign.system later, but for now let me point-out that while it draws on an AC power-line, it actually only makes use of just one DC-pulse -(that's a half-cycle of AC), in order to produce it's ign.spark.
I've already posted (a few months back) on how it works off-from it's four-pole alternator.
To help find those other postings, you could try doing a search for the word 'magneto'.
" I think I’m OK on the battery ignition though. "
____ Indeed you very well may be, Mike,, as from what I've read of your's this last time, it now seems that I likely misunderstood what I had read of what you then seemed to have been meaning to state.
So I'd like to put what I had previously thought you were meaning to claim, into my own wording, for you to then proclaim as correct, or, mistaken by me, (so as to clear-up the confusion). ...
____ Please note that the following is in reference only to battery-powered ign.systems...
__ I had thought that you were saying that the condenser helps prevent excessive arcing across the points-gap because the high-voltage that's been induced into the ign.coil (from the collapsing flux-field), would be shared with & tend charge the condenser towards an equally high-voltage, so thus once the points separated, the high-voltage supplied from the ign.coil would remain on one side of the point-gap, while the then about-equal high-voltage supplied from the charged condenser would remain on the opposite side of the points-gap. _ And thus since the two contacts would then be at about equal potential, there would then be reduced potential-difference between them, so as to thus help prevent arcing across the points-gap.
__ That particular line-of-thought is what I was (then) able to conclude that you had theorized, (after having tried to make some sense of what you had written).
If I had then known that you were properly-educated on this stuff, I then would've kept-at trying to make better-sense of your wording to make it fit the actual-facts.
And I'm glad that you have not re-edited your previous wording so that I can soon take another shot at understanding it (correctly?).
__ Now if you yourself can see how I got it wrong from your previous-wording, then please respond to you own post, retaining the before-wording plus any after-wording which you'd now instead use to keep me from going off-track, (like it seems I must-ve).
__ Now that possible misinterpretation (which I may have [likely] made) from your wording, does indeed seem to make a kind of real-sense, however (as I had pointed-out in that previous-exchange), it really doesn't (seem to me to) correctly match-up with the actual lay-out of the electrical-connections of all the involved parts.
So I'll now await you response, (if you have any yet), to address this stuff (which I've just brought-up in this section of my post here).
" I still stand by my comment though, that an open condenser will not keep your ignition from operating be it battery or ac magneto. A shorted one will stop you dead in your tracks. "
____ I never bothered to comment on your previous wording concerning these claims, simply because they were true. _ Sorry if any of my response-wording allowed you to think that I may not have agreed with those facts !
Furthermore, I have & will only make comments about any of your wording, only when I either believe it to be wrong or, it too easily allows for misinterpretation.
(And I, [unlike others here in the past], would never get upset if anyone ever has any issues with any wording that I ever submit ! _ In fact, I may even appreciate it.)
" I think I should leave that previous post unaltered,
as without it your post looses context and meaning for those who want to see what you and I are talking about. "
____ That's quite thoughtful of you ! _ Although I'm thinking that there's probably less than a handful here who will bother to try to understand it all. _ And that being the case, after this thread falls to the lower half of the page (of all the other threads), I think we should then just delete our errored wording so that others in the future need not wade-through any garbage just to get to the good-points.
" the non grounded side of the points would see the full potential, probably at least a few hundred volts at the instant they open. "
____ This touches on the point that I was so extensive on, about how the ign.coil's flux-induced primary-circuit current-flow will in no way be stopped even when the points open & try to turn-off the circuit they had started, thus (without the desired function of a condenser), the ultra-motivated flow of electrons simply-must create whatever voltage is necessary in order to jump the gap between the points ! _ And that may be more than just a "few hundred volts". _ (A geek could figure-out the exact voltage that's involved at the gap, by figuring the actual resistance of the air between the open points and after measuring the amperage of the current-flow (that was going through the points), he could then easily calculate what the actual voltage must be (to pass-through the points-gap) ! - (That is, by the way, without a condenser connected to instead simply absorb the forced batch of electrons).
" then over an unknown period of time the cap will charge attempting to reach the full potential of what ever voltage is applied to the non grounded side. In truth we are seeing a dynamic event here and as the cap is charging, the voltage supplied on the non grounded side is changing. So we don’t know what values are actually being felt there, "
____ Here I assume that you're thinking that since the points could be subjected to at least hundreds of volts, that then it ought be that the condenser also must be getting charged with about the same amount of voltage.
Well actually however, the condenser -("cap") will not be exposed to higher voltages than that of the battery until after it's storage-capacity has been reached, then at that point it will have to withstand the same (possibly high) voltage as the contact-points are still having to do, (if indeed they still are having to deal with more voltage [than that of the battery], by that same point),, and just after the flux-field has collapsed, the condenser will then only be charged to just the same voltage as the battery (until it's next shorted to ground by the points).
Getting back to the exact-moment when the condenser may begin to charge to a higher voltage than that of the battery,, it is hoped that by that very same moment, the flux-field has by then collapsed and the contact-points are by then also all-done with needing to block ANY current-flow -(both battery-forced & especially FLUX-forced).
This (hopefully) convenient-coincidence is the reason why the condenser's capacity is chosen to be of a particular-size which will just hold the expected charge-size of the electrons under flux-force, so as to make for as perfect of a fit as possible. _ Because of course, condenser-capacity that's too small will not protect the contact-points well enough, and conversely, a capacity that's too-large will tend to damage the contacts in the opposite direction.
So, if life were all about saving the contact-surfaces of the points, then we'd all be talking about what the perfect sized condenser-capacity is for each of our particular ign.systems. _ Fortunately, they're all pretty close enough (capacity wise), that we need not be concerned with that !
. . .
" I only mention these relationships to account for why I have not fully figured out what is going on in the non battery ignitions. "
____ That's because you're (like most everyone else), looking at the non-battery ign.system as if it actually works on AC (as many others, including some manuals, would have you think)...
But actually, that ign.system is also DC-powered !!!
" as in looking at the circuit, I could envision a stronger spark being built when you close the points and create a very low resistance path for the current to go to and create potentially a more rapid collapse of the field. Perhaps a second spark is produced "
____ In order to follow that thought, it could stand to be further explained & in other words as well.
Also, we need to make sure we are referring to the exact-same ign.circuit lay-out.
Anyone got a schematic-pic to post, of it?
__ The involved circuit as Ducati has it, along with the related points-cam being shaped as it is, probably can't produce your expected reverse-spark, since by the time the cam-lobe lets the points close, there's then no (significant) alt.power still being offered to the ign.coil.
And also, even if there were significant alt.power-juice available at that time, the short-circuit through the (then closed) contact-points would likely be better able to rob the ign.coil of it's then established current-flow, if only the ign.coil had a far greater impedance than it actually has.
____ Decades ago, I had tried-out wiring the alternator-powered ign.circuit to be just the same as the battery-powered ign.circuit, thus creating the (alt.powered) ign.spark at the moment the points open & collapse the flux-feild, to then get that circuit's resulting spark, (just as you have figured would work) ! _ And while that type of (non-Ducati) ign.circuit would start & run the motor,, for some reason (which I never worked-out), it would only allow a DUKE to run for a few miles, and then die,, not being able to run again, until after sitting a while ! _ The (battery-type) ign.coil would get quite hot, but still allow starting again, well before cooling-off any notable amount.
That was an ign.circuit type which I always wanted to get all sorted-out, but unfortunately never got around to fully check-into, (as there were known to be good ign.circuits to use instead!).
" That may be why I'm having trouble following all of what you are saying towards the end of the discussion. "
____ Wish you had quoted that part of my wording, so that I could offer it explained in some other way, otherwise I'm not sure of exactly what you're referring to.
" But you don’t acknowledge that the collapsing field causes a much higher voltage to be induced in the secondary than the turns ratio alone would account for. "
____ That's because if I were ever before made aware of any such additional magic applicable to ign.coils, I've forgotten about it !
" But it is governed by Faradays law which states that the amount of voltage induced in an inductor is dependant on the amount of flux, the number of turns, and the time rate of cutting.
Fields collapse usually faster than they are built. So we add greatly to the secondary output if we collapse the field more quickly which causes the lines of flux to cut the turns faster and therefore creating much bigger voltages. "
____ I don't see how that cutting-rate effect could be made to make any major/useful difference for either of the ign.systems, since no extra component/circuits are employed to be able to cause any effect on those build/collapse-rates.
__ That added ("magical") effect must be resultant of the "cutting" -(or rate of flux-collapse?), as I'm unfamiliar with that cutting-rate effect being able to make any difference in relation to ignition-coil operation, since the ign.coil-circuits do not employ any device or resulting-effect (that I know of) which could speed-up or slow-down the rate of the magnetic-flux build-up or collapse.
That rate of "cutting" effect comes into-play with things like alt.rotor-speed, but with ign.coils, the rate of flux build-up & collapse is already completed as fast as it can possibly be done ! _ And also, I really can't see how building-up the flux-field more slowly, (even if a device/circuit were actually employed within the ign.system, so that the flux-field would purposely build-up much slower than it collapses), could possibly assist in later causing a higher voltage than the turns-ratio accounts for, when the field next collapses at it's normal/full-speed rate. _ Such an extra-bonus as that, (if true), seems like unaccountable magic to me. _ So I don't think there's any such flux-field speed-ratio actually occurring with the ign.coil, to also help increase the spark-voltage.
__ I'm wondering if you yourself simply applied the Faraday's-law to the ign.coil, while assuming that there must be such an effect with it's operation, (as well as things like alternators) ? _ Or, if you were actually taught that that law is indeed applicable to ign.coil-circuits ?
" the condenser is not totally effective in its job. I think that at the instance the points open, it bleeds off a lot of current, but because it is charging it begins to oppose current flow as it goes towards acting like an open, the path across the points becomes the lower impedance option and some spark does jump across them. Optimally, the voltage will have dropped enough by that time to lessen the damage to the points. "
____ That all seems like reasonable-thinking to me, but I wonder what that remaining voltage amount actually is, and if a somewhat larger condenser-capacity might further calm it down even more-so !?
Fun-Cheers,
-Bob
____ Well that's exactly the very same way I've already been looking at posting most of my posts here at this w.site, Mike ! _ If I hadn't already felt that way, I wouldn't have bothered with my extended response to your previous-post.
Glad that you seem to agree with my inclination !
" And you are right; I got it wrong as it pertains to the AC ignition system. "
____ We'll no doubt get further into that odd-working ign.system later, but for now let me point-out that while it draws on an AC power-line, it actually only makes use of just one DC-pulse -(that's a half-cycle of AC), in order to produce it's ign.spark.
I've already posted (a few months back) on how it works off-from it's four-pole alternator.
To help find those other postings, you could try doing a search for the word 'magneto'.
" I think I’m OK on the battery ignition though. "
____ Indeed you very well may be, Mike,, as from what I've read of your's this last time, it now seems that I likely misunderstood what I had read of what you then seemed to have been meaning to state.
So I'd like to put what I had previously thought you were meaning to claim, into my own wording, for you to then proclaim as correct, or, mistaken by me, (so as to clear-up the confusion). ...
____ Please note that the following is in reference only to battery-powered ign.systems...
__ I had thought that you were saying that the condenser helps prevent excessive arcing across the points-gap because the high-voltage that's been induced into the ign.coil (from the collapsing flux-field), would be shared with & tend charge the condenser towards an equally high-voltage, so thus once the points separated, the high-voltage supplied from the ign.coil would remain on one side of the point-gap, while the then about-equal high-voltage supplied from the charged condenser would remain on the opposite side of the points-gap. _ And thus since the two contacts would then be at about equal potential, there would then be reduced potential-difference between them, so as to thus help prevent arcing across the points-gap.
__ That particular line-of-thought is what I was (then) able to conclude that you had theorized, (after having tried to make some sense of what you had written).
If I had then known that you were properly-educated on this stuff, I then would've kept-at trying to make better-sense of your wording to make it fit the actual-facts.
And I'm glad that you have not re-edited your previous wording so that I can soon take another shot at understanding it (correctly?).
__ Now if you yourself can see how I got it wrong from your previous-wording, then please respond to you own post, retaining the before-wording plus any after-wording which you'd now instead use to keep me from going off-track, (like it seems I must-ve).
__ Now that possible misinterpretation (which I may have [likely] made) from your wording, does indeed seem to make a kind of real-sense, however (as I had pointed-out in that previous-exchange), it really doesn't (seem to me to) correctly match-up with the actual lay-out of the electrical-connections of all the involved parts.
So I'll now await you response, (if you have any yet), to address this stuff (which I've just brought-up in this section of my post here).
" I still stand by my comment though, that an open condenser will not keep your ignition from operating be it battery or ac magneto. A shorted one will stop you dead in your tracks. "
____ I never bothered to comment on your previous wording concerning these claims, simply because they were true. _ Sorry if any of my response-wording allowed you to think that I may not have agreed with those facts !
Furthermore, I have & will only make comments about any of your wording, only when I either believe it to be wrong or, it too easily allows for misinterpretation.
(And I, [unlike others here in the past], would never get upset if anyone ever has any issues with any wording that I ever submit ! _ In fact, I may even appreciate it.)
" I think I should leave that previous post unaltered,
as without it your post looses context and meaning for those who want to see what you and I are talking about. "
____ That's quite thoughtful of you ! _ Although I'm thinking that there's probably less than a handful here who will bother to try to understand it all. _ And that being the case, after this thread falls to the lower half of the page (of all the other threads), I think we should then just delete our errored wording so that others in the future need not wade-through any garbage just to get to the good-points.
" the non grounded side of the points would see the full potential, probably at least a few hundred volts at the instant they open. "
____ This touches on the point that I was so extensive on, about how the ign.coil's flux-induced primary-circuit current-flow will in no way be stopped even when the points open & try to turn-off the circuit they had started, thus (without the desired function of a condenser), the ultra-motivated flow of electrons simply-must create whatever voltage is necessary in order to jump the gap between the points ! _ And that may be more than just a "few hundred volts". _ (A geek could figure-out the exact voltage that's involved at the gap, by figuring the actual resistance of the air between the open points and after measuring the amperage of the current-flow (that was going through the points), he could then easily calculate what the actual voltage must be (to pass-through the points-gap) ! - (That is, by the way, without a condenser connected to instead simply absorb the forced batch of electrons).
" then over an unknown period of time the cap will charge attempting to reach the full potential of what ever voltage is applied to the non grounded side. In truth we are seeing a dynamic event here and as the cap is charging, the voltage supplied on the non grounded side is changing. So we don’t know what values are actually being felt there, "
____ Here I assume that you're thinking that since the points could be subjected to at least hundreds of volts, that then it ought be that the condenser also must be getting charged with about the same amount of voltage.
Well actually however, the condenser -("cap") will not be exposed to higher voltages than that of the battery until after it's storage-capacity has been reached, then at that point it will have to withstand the same (possibly high) voltage as the contact-points are still having to do, (if indeed they still are having to deal with more voltage [than that of the battery], by that same point),, and just after the flux-field has collapsed, the condenser will then only be charged to just the same voltage as the battery (until it's next shorted to ground by the points).
Getting back to the exact-moment when the condenser may begin to charge to a higher voltage than that of the battery,, it is hoped that by that very same moment, the flux-field has by then collapsed and the contact-points are by then also all-done with needing to block ANY current-flow -(both battery-forced & especially FLUX-forced).
This (hopefully) convenient-coincidence is the reason why the condenser's capacity is chosen to be of a particular-size which will just hold the expected charge-size of the electrons under flux-force, so as to make for as perfect of a fit as possible. _ Because of course, condenser-capacity that's too small will not protect the contact-points well enough, and conversely, a capacity that's too-large will tend to damage the contacts in the opposite direction.
So, if life were all about saving the contact-surfaces of the points, then we'd all be talking about what the perfect sized condenser-capacity is for each of our particular ign.systems. _ Fortunately, they're all pretty close enough (capacity wise), that we need not be concerned with that !
. . .
" I only mention these relationships to account for why I have not fully figured out what is going on in the non battery ignitions. "
____ That's because you're (like most everyone else), looking at the non-battery ign.system as if it actually works on AC (as many others, including some manuals, would have you think)...
But actually, that ign.system is also DC-powered !!!
" as in looking at the circuit, I could envision a stronger spark being built when you close the points and create a very low resistance path for the current to go to and create potentially a more rapid collapse of the field. Perhaps a second spark is produced "
____ In order to follow that thought, it could stand to be further explained & in other words as well.
Also, we need to make sure we are referring to the exact-same ign.circuit lay-out.
Anyone got a schematic-pic to post, of it?
__ The involved circuit as Ducati has it, along with the related points-cam being shaped as it is, probably can't produce your expected reverse-spark, since by the time the cam-lobe lets the points close, there's then no (significant) alt.power still being offered to the ign.coil.
And also, even if there were significant alt.power-juice available at that time, the short-circuit through the (then closed) contact-points would likely be better able to rob the ign.coil of it's then established current-flow, if only the ign.coil had a far greater impedance than it actually has.
____ Decades ago, I had tried-out wiring the alternator-powered ign.circuit to be just the same as the battery-powered ign.circuit, thus creating the (alt.powered) ign.spark at the moment the points open & collapse the flux-feild, to then get that circuit's resulting spark, (just as you have figured would work) ! _ And while that type of (non-Ducati) ign.circuit would start & run the motor,, for some reason (which I never worked-out), it would only allow a DUKE to run for a few miles, and then die,, not being able to run again, until after sitting a while ! _ The (battery-type) ign.coil would get quite hot, but still allow starting again, well before cooling-off any notable amount.
That was an ign.circuit type which I always wanted to get all sorted-out, but unfortunately never got around to fully check-into, (as there were known to be good ign.circuits to use instead!).
" That may be why I'm having trouble following all of what you are saying towards the end of the discussion. "
____ Wish you had quoted that part of my wording, so that I could offer it explained in some other way, otherwise I'm not sure of exactly what you're referring to.
" But you don’t acknowledge that the collapsing field causes a much higher voltage to be induced in the secondary than the turns ratio alone would account for. "
____ That's because if I were ever before made aware of any such additional magic applicable to ign.coils, I've forgotten about it !
" But it is governed by Faradays law which states that the amount of voltage induced in an inductor is dependant on the amount of flux, the number of turns, and the time rate of cutting.
Fields collapse usually faster than they are built. So we add greatly to the secondary output if we collapse the field more quickly which causes the lines of flux to cut the turns faster and therefore creating much bigger voltages. "
____ I don't see how that cutting-rate effect could be made to make any major/useful difference for either of the ign.systems, since no extra component/circuits are employed to be able to cause any effect on those build/collapse-rates.
__ That added ("magical") effect must be resultant of the "cutting" -(or rate of flux-collapse?), as I'm unfamiliar with that cutting-rate effect being able to make any difference in relation to ignition-coil operation, since the ign.coil-circuits do not employ any device or resulting-effect (that I know of) which could speed-up or slow-down the rate of the magnetic-flux build-up or collapse.
That rate of "cutting" effect comes into-play with things like alt.rotor-speed, but with ign.coils, the rate of flux build-up & collapse is already completed as fast as it can possibly be done ! _ And also, I really can't see how building-up the flux-field more slowly, (even if a device/circuit were actually employed within the ign.system, so that the flux-field would purposely build-up much slower than it collapses), could possibly assist in later causing a higher voltage than the turns-ratio accounts for, when the field next collapses at it's normal/full-speed rate. _ Such an extra-bonus as that, (if true), seems like unaccountable magic to me. _ So I don't think there's any such flux-field speed-ratio actually occurring with the ign.coil, to also help increase the spark-voltage.
__ I'm wondering if you yourself simply applied the Faraday's-law to the ign.coil, while assuming that there must be such an effect with it's operation, (as well as things like alternators) ? _ Or, if you were actually taught that that law is indeed applicable to ign.coil-circuits ?
" the condenser is not totally effective in its job. I think that at the instance the points open, it bleeds off a lot of current, but because it is charging it begins to oppose current flow as it goes towards acting like an open, the path across the points becomes the lower impedance option and some spark does jump across them. Optimally, the voltage will have dropped enough by that time to lessen the damage to the points. "
____ That all seems like reasonable-thinking to me, but I wonder what that remaining voltage amount actually is, and if a somewhat larger condenser-capacity might further calm it down even more-so !?
Fun-Cheers,
-Bob
PLEASE NOTE... If this-post is not-yet signed-off with '-Bob', then I'm still in the process of completing it,, and if not also included with 'DCT' near bottom as well, then I may edit this post's wording at a later time. - Dct.Bob
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MotoMike
- Posts: 487
- Joined: Wed Aug 04, 2010 3:40 am
Re: Magneto ignition system diagnosis
MotoMike wrote:***As Bob suggested, I have re-read this post and agree that it has room for improvement. This next passage makes sense to me, but I see in close reading of the wording that one might think I mean the "charged" capacitor results in less difference of potential across the points. It is the Charging of the capacitor that results in less difference of potential across the points. without the capacitor there, as soon as the points open the full potential would be felt at the non grounded point and a serious arc would jump to the other point.***
"In truth you don't need a condenser in there to make your ignition work. It serves as a breaker points preservation device. The condenser is a capacitor that charges up to give less difference of potential between the two contacts of the points when they open."
***And in reading the following passage, I see more confusion. It is even less illustrative that the act of charging is the important aspect. The cap's job is to charge and by doing so create no difference of potential at the instant the points open. I was not clear here and see that it looks as if I mean that they are charged before the points open. They are not; with the points closed there is ground potential on both sides of the cap. With the points closed the cap is discharged. So at the instant the points open they have the same ground value, this difference of potential increases as the points open and the field further collapses and the cap charges. Since contact points do wear in a correctly functioning system, we can see that the cap/condenser is not totally effective, but mitigates the damage. Again without the cap performing this charging function, the full potential of the collapsing field would be felt at the non grounded point and a spark would jump hotly to the grounded point.***
"and the job of the condenser is to charge to some portion of this large voltage value. Then when the points open, there is less difference of potential between them and less arc drawn across them". .
Sorry if this caused confusion. I can see how it would.
Regards
Mike
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ajleone
- Posts: 231
- Joined: Sat Oct 31, 2009 11:20 pm
- Location: Pittsford, NY
- Contact:
Re: Magneto ignition system diagnosis
Interesting discussion and information !
My question still stands on the question of the charging coil tests:
I am still not clear if there is a simple way to test the chargin coil. I am not convinced that a basic multimeter ohm check is the way to go.
For the condensor, In the Ducati maintenance books, they claim that you can charge the condensor with a battery and then short the lead to the case and get a spark. I have not been able to do this - anyone else ?
Next time, clean the points first and unless something obviouly broke, it probably did not.
Tony
My question still stands on the question of the charging coil tests:
I am still not clear if there is a simple way to test the chargin coil. I am not convinced that a basic multimeter ohm check is the way to go.
For the condensor, In the Ducati maintenance books, they claim that you can charge the condensor with a battery and then short the lead to the case and get a spark. I have not been able to do this - anyone else ?
Next time, clean the points first and unless something obviouly broke, it probably did not.
Tony
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DewCatTea-Bob
- Posts: 2897
- Joined: Sun Nov 01, 2009 10:53 am
- Location: Near SE side of Lake Michigan
Re: Magneto ignition system diagnosis
" I am still not clear if there is a simple way to test the chargin coil. I am not convinced that a basic multimeter ohm check is the way to go. "
____ Other than that simple test, there's no other way other than to do an actual 'bench-test', and since you don't have such an external set-up to work with, you'll just have to install it and test it out, that way.
" For the condensor,
they claim that you can charge the condensor with a battery and then short the lead to the case and get a spark. I have not been able to do this "
____ Then either it's bad or you're not doing it properly. _ (As I assume you know that the resulted sparking will not be much like an ign.spark.)
After the battery has been connected to the condenser's case & lead, take it into a dark room and lightly scratch it's lead-end against it's metal-casing, so as to make sure that it's indeed really not sparking.
_____ As for the latest post by Mike, it's now very clear that I had certainly indeed misunderstood what he had actually meant to convey with his original wording !
And his latest/revised wording (which also discusses his previous [less clear] wording), all makes good sense to me now !
__ Furthermore, I think that once this thread has wound-down, Mike & I should agree to re-edit our off-topic posts (since much of it is based on mistakes), and move them out & over to another thread dedicated to battery-type ignition-operation details.
I believe I have this ability but, don't really wish to try it without Jim's approval.
Hopeful-Cheers,
-Bob
____ Other than that simple test, there's no other way other than to do an actual 'bench-test', and since you don't have such an external set-up to work with, you'll just have to install it and test it out, that way.
" For the condensor,
they claim that you can charge the condensor with a battery and then short the lead to the case and get a spark. I have not been able to do this "
____ Then either it's bad or you're not doing it properly. _ (As I assume you know that the resulted sparking will not be much like an ign.spark.)
After the battery has been connected to the condenser's case & lead, take it into a dark room and lightly scratch it's lead-end against it's metal-casing, so as to make sure that it's indeed really not sparking.
_____ As for the latest post by Mike, it's now very clear that I had certainly indeed misunderstood what he had actually meant to convey with his original wording !
And his latest/revised wording (which also discusses his previous [less clear] wording), all makes good sense to me now !
__ Furthermore, I think that once this thread has wound-down, Mike & I should agree to re-edit our off-topic posts (since much of it is based on mistakes), and move them out & over to another thread dedicated to battery-type ignition-operation details.
I believe I have this ability but, don't really wish to try it without Jim's approval.
Hopeful-Cheers,
-Bob
PLEASE NOTE... If this-post is not-yet signed-off with '-Bob', then I'm still in the process of completing it,, and if not also included with 'DCT' near bottom as well, then I may edit this post's wording at a later time. - Dct.Bob
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