Magneto dead?

[DewCatTea-Bob]

" It's as if the new condenser is bad. When I say the condenser was new, I mean it was "New-In-Box", but I don't mean it was fresh. The condenser is quite likely from the 1960s or 70s.

____ The magneto-TYPE -(actually E.T.) ignition-systems don't require a condenser for exactly the very same purpose as is needed for battery-powered type ign.systems, and in-fact for these AC.supplied/DC.pulse powered (magneto-type!)- ign.systems, the condenser is not really very important (as it is for the battery-powered type).


" I believe these things are by nature electrolytic capacitors which have some impregnated electrolyte inside. Perhaps the electrolyte dried up inside and reduced or ruined the effectiveness of the capacitor. "

____ Not at all likely, (I'm sorry to declare) ! ...
While a 'condenser' may be referred-to as a "capacitor", an electrolytic-cap. can't really be used as a 'condenser', (cuz for one thing, e.caps must be polarized !).
The Ducati-condenser is as all others condensers... It's a dual-roll of foil-layers with a layer of insulation between them. _ And polarization is not a concern as it is with an e.cap.
__ (The current-state of confusion between condensers & capacitors wouldn't be such as it has become these-days, if it weren't for so many such things getting dumbed-down so prevalently.)


" I think my next step is to change the points and condenser and try again.
Opinions are welcomed..... "

____ My opinion is that (while the condenser may be of other than the most optimum value), the points, once thoroughly cleaned, ought then work as good as new. _ And you can simply make sure they're gaped as you had them initially done, (so as to avoid the extra trouble of installing & setting a new pair).


____ Besides the confusion set-forth by our improperly-trained elders concerning the exact meanings of the words 'condenser & 'capacitor' , it's become obvious that even the best of us have also been lead-astray by them as to the actual difference between an 'energy-transfer ign.system' (as is actually employed by the AC.powered Duke-models), and a REAL "magneto" ! ...
ORIGINALLY, (in respect to just AC.production devices),, a 'magneto' was (and can of-course still be) merely a stator-winding with rotaing magnetic-fields, while an 'alternator' was pretty-much just the same except with the stationary & rotating aspects reversed.
However in respect to motorcycles, either is an alternator -(a spinning mechanical-device which produces AC.power, [unlike a 'generator' which produces DC.power] ),, while a "magneto" has come to become known as a single self-contained device which includes ALL the stages required to produce & provide the high-tension spark DIRECTLY to the spark-plug !
While the (magneto like) energy-transfer ign.system (employed on a few Duke-models), does all the same, but with all the involved stages spread-out over separate locations.
__ This explanation should help clear-up the confusion over just what a "magneto" actually is supposed to be (in reference to when) on a motorcycle,
(at least in the USA).

[JimF]

Hi Bob,

You know it never dawned on me about the AC nature of the system voltage and thus what effect the capacitor has.

BUT- that being said, I changed the cap and - BINGO! She's alive again!

I will do a post-mortem on the cap I took out. I had checked it days ago to be sure it wasn't shorted. I will check the capacitance tomorrow.

You know the caps I have in boxed from Ducati that appear to be decades old have sort of a rubber cap on the end of the cylinder where the wire comes out. It's not exactly like modern caps that are better sealed.

I have now put RTV around the points wire where it enters the engine.

Your help has been great and I thank you for it and the encouragement given when I got frustrated.

It's so nice to have the 250 alive again.

Jim

[DewCatTea-Bob]

" You know it never dawned on me about the AC nature of the system voltage and thus what effect the capacitor has. "

____ Well, with respect to the ign.system's current-flow (which is what I assume you actually meant by "system voltage"), it's just as well that such AC.flow had not dawned on you before,, cuz actually, the ign.system really just makes use of only a single pulse of DC, (and ignores the rest of the supplied AC !).
However a condenser does allow current-flow in both directions, (whereas an electrolytic-capacitor* will not accept reverse charging).
(* The short-term 'cap' is most-often used in reference to an electrolytic-capacitor, but ought not be used in reference to a condenser,, as those two electronic-components are not actually very much the same.)


" I will do a post-mortem on the cap I took out. "

____ It's quite rare for even a used condenser to 'go-bad', so an unused/NOS unit should be even less suspect.
And it's rating/value should not effect whether or not ign.spark is created, so when you removed the condenser, you must've then also removed a short-circuit from somewhere. _ Perhaps the condenser-wire was in some contact with something grounded, (if the condenser itself is not internally shorted).
__ (NOW it's looking like Bill hit the issue on the head.)


" the caps I have in boxed from Ducati that appear to be decades old have sort of a rubber cap on the end of the cylinder where the wire comes out. "

____ Then perhaps that rubber-cap has since given-out a bit and allows it's wire to make a partial contact short-circuit.


" Your help has been great and I thank you for it and the encouragement given when I got frustrated. "

____ Of-course you're welcome for whatever I-MYSELF helped you with, and I hope you weren't too discouraged by my silly-comment about Gremlin-repellent.


Duke-Cheers,
-Bob

[JimF]

Well, the post-mortem for the condenser may have been premature. From the standpoint of capacitance the condenser I removed from service yesterday is nearly identical in value to the condenser I installed yesterday (0.49 uF.)

I could do a hi-pot test on the condenser, but I would need to know an upper voltage limit so as not to destroy it just to find out it wasn't bad until after I destroyed it with the hi-pot.

This could mean that at some undetermined point in my troubleshooting that I re-oriented or replaced something, unknowingly either opening a short circuit or closing an open circuit. It seems likely that it would have been around the points plate as that is where I was last working so perhaps you are correct about me removing a short, but keep in mind that when this problem began almost a week ago I was quick to put an audible continuity tester on the points wire (removed from the ignition coil) and as I spun the engine the interrupting audible noise told me the points were opening and closing - and thus not shorted to the frame which is why I spent so much early effort troubleshooting on the magneto side of the bike.

Or course the best test of the suspect condenser would probably be to switch back to the suspect condenser as I think that if the bike continued to run with it would be very interesting. However, time is against me as I have a lot going on for the next few weeks. I need the bike to be operational for an event (Chicago's Mods vs. Rockers) a week from Saturday and I have time-consuming commitments to my day job, my side job and my side job's side job not to mention my family.


Jim

[DewCatTea-Bob]

" I could do a hi-pot test on the condenser, but I would need to know an upper voltage limit so as not to destroy it just to find out it wasn't bad until after I destroyed it with the hi-pot. "

____ I'm not positive but I would think up to 15-volts would be safe to go-up to, without reaching whatever it's actual breakdown-voltage happens to be,, (certainly 60-volts would do it in).


" This could mean that at some undetermined point in my troubleshooting that I re-oriented or replaced something, unknowingly either opening a short circuit
It seems likely that it would have been around the points plate as that is where I was last working so perhaps you are correct about me removing a short, but keep in mind that when this problem began almost a week ago I was quick to put an audible continuity tester on the points wire (removed from the ignition coil) and as I spun the engine the interrupting audible noise told me the points were opening and closing - and thus not shorted to the frame which is why I spent so much early effort troubleshooting on the magneto side of the bike. "
Or course the best test of the suspect condenser would probably be to switch back to the suspect condenser as I think that if the bike continued to run with it would be very interesting.

____ Perhaps you just happened to have two separate causes of the related issue ? - (The original plus another-one you may've caused while trouble-shooting.)
__ Many times (while trouble-shooting the work of others), I've found that at least one of the three fiber-washers (especially the smallest/center piece) had been lost from the place where the tiny bolt fits-through the points-spring mount,, thus allowing a MYSTERY-ground connection-leak through to the points-plate.
And another has been where the ign.coil-wire's wire-terminal is left sticking-up/out so far, as to then come in contact with the points-cover, once that inspection-cover is reinstalled.
These are just two of such gremlin-type/non-obvious unintentional short-circuits that come-to-mind, which may be the type of thing that could be players within your system.


Duke-Cheers,
-Bob