Alternator rotor stator alignment

[Rick]

DCT Bob- Thanks for your description, it sounds like a solenoid- I hadn't made that connection.
I don't want to put words in your mouth, so I'll add a couple of drawings and my description to see if you think I've got it right.
The rotor pole pieces create the magnetic field on the left, and that field induces the field around the stator limb.

rotor and limb fields sm.jpg

The winding coil is stationary- my recollection was of a coil moving through a field, so the field needs to move across the coil to induce current. As the rotor rotates, the alternating polarity of the pole pieces changes the polarity of the stator limb, and a sort of pulsating, back and forth movement of the field induces an alternating current in the winding- or, I need to study more...

MOVING FIELD.jpg

Jordan- I'm trying to work this out on a bench, so spinning the parts and triggering/capturing a little pulse sounds like a lot of work- I'll need to read what DCT Bob suggested and give it some thought.
Rick

[DewCatTea-Bob]

[quote= Rick ...
" Thanks for your description, it sounds like a solenoid- I hadn't made that connection. "

____ Not sure I get your analogy.



" The rotor pole pieces create the magnetic field
and that field induces the field around the stator limb. "

____ Instead of "around", it's rather more like 'into' or 'through' the stator-limb/coil-core.
__ The 'core' of stator-coils has to be made of a kind of softened iron-alloy that will easily temporally adopt magnetic-bias as fully as possible, yet capable of instantly dropping any such induced polaric-bias without retaining much left over.



" my recollection was of a coil moving through a field, "

____ That seems rather like a generator.



" or, I need to study more... "

____ I'd say not, or-else you'll then be able to tell me more detailed aspects of which I may not yet be aware of !



____ If you've looked-over the post & thread which I left a link to, then I hope you understood that the plotted yellow-line was intended for locating a timing-mark only for engines employing the 22-degree static-ign.timing. _ Your Monza-type stator/rotors would require less degrees of rotor-advance.


Duke-Cheers,
-Bob

[Rick]

Thanks for the help Bob- I plan to work on some 'wiring for beginners' diagrams, but will certainly need more advice.
Rick

[Jordan]

I meant the 'scope's trigger control for stabilizing the display might need to be set to external, with some input from the ignition.
In addition, a waveform from the ignition circuit is needed on one channel, as well as the alternator's on the other. Superimposed, there'd be a clear picture of actual events.
Shouldn't be a problem to have a usefully viewable display, even with varying revs on a basic 'scope.
It isn't the easiest thing to organize I suppose, but avoids a lot of theorizing.

[quote= Jordan ...
" The trigger would be from the ignition lead? "

____ No need to involve the high-tension output to the o.scope, as one of it's inputs can rather simply be set-up to display the ign.power-coil's AC.output as the engine-revs are kept steady.
The o.scope's other input could be fed with the lighting-coil's output for comparison (if so desired), since it's rather steady & unbroken AC.frequency-output is virtually the same as that of the other AC.output that's in question. _ And since that ign.power-coil's output will be dead while the contact -points are shut,, then when the points open and thus-then allow the o.scope to test it's then fully-available waveform for display, it can then be seen exactly what part of that waveform has become useable for the ign.system.
__ The real trick for getting a good/solid look at the resulting waveform, would be keeping the engine-revs steady long enough to realize what's being shown.
I imagine modern o.scopes ought have a flash-shot memory to hold-still a preferred snap-shot of the otherwise wavering display.

[tobydmv]

Thanks for the help Bob- I plan to work on some 'wiring for beginners' diagrams, but will certainly need more advice.
Rick

Rick, if you could please do that I would be eternally grateful. I have never had to do this on any other bike including Benelli, Motobi, Moto Morini, Gilera, Guzzi, Minarelli, Triumph..... Why didnt ducati just put a woodruff keyway for the rotor if they meant it to be indexed? Oh well, maybe they figured it would never be disturbed since the cb points are conveniently located outside the cases.
t

[Nick]

No woodruff key — my suspicion is that they were afraid of weakening the crank.

[DewCatTea-Bob]

by: tobydmv ...
" Why didnt ducati just put a woodruff keyway for the rotor if they meant it to be indexed? "

____ I've never really examined all the various 4-pole rotors (from different engine-models) for any un-obvious physical-alterations between them, and-so I assume they're all pretty-much the same,, but yet, the same 4-pole rotor-design needs to be fitted to a number of different engine-models with differing static-ign.timing settings. _ So just a single key-way slot would make the mag.rotors non-interchangeable and-thus more of a mass-production complication for such key-way indexing.



" maybe they figured it would never be disturbed since the cb points are conveniently located outside the cases. "

____ The only 4-stroke Ducati-engine I know-of that located the contact-points behind the mag.rotor, was the 125-Bronco,, of which, did employ key-way slots in rotor & crankshaft.




[quote= Nick ...
" No woodruff key — my suspicion is that they were afraid of weakening the crank. "

____ Well there is already the one in the same area that's used for the drive-gear,, so any more than that located so near-by, would probably indeed have been such a concern.


Dukaddy-DUKEs,
-Bob

[ducwiz]

I never understood why it should be important to adjust the flywheel angular position in an engine with D. C. ignition. My point of view: The instantaneous power used for the spark is taken from the battery, which has continuously plenty of power, the max. AC power point is unimportant.
In an A.C. ignition however, it is of utmost importance to have the spark timing adjusted to the "abridgement" or "breakdown" of the magnetic field between yokes and permanent magnets, because this is the point of max. available energy for the HV coil.

The flywheel position may also play a role with respect to the inertial balance, but I never found any information issued by DUCATI about that point.

cheers Hans

[DewCatTea-Bob]

____ Thanks for posting that complete list covering the n-c.models, Hans !
I've now taken it and created a condensed version with just the data that's more pertinently related to this thread, (as seen posted down-below).



[quote= ducwiz ...
" I never understood why it should be important to adjust the flywheel angular position in an engine with D. C. ignition. "

____ I've given explanation for Ducati's likely concern for such efficiency-detail even for their non-AC.powered ign.systems, at-least once before. _ So I must assume that either you've forgotten or missed it, cuz I'm sure that at-least the likes of yourself would be able to understand the explanation.



" The instantaneous power used for the spark is taken from the battery, which has continuously plenty of power,
the max. AC power point is unimportant. "

____ While I really don't agree that you are 100% right,
of-course you are-not incorrect about the timing of the power-pulse peak being "unimportant",, since a well charged battery will certainly power the ign.system all by itself, without any help from the charging-system !
However even with battery-powered ign.systems, there's at-least two worthwhile reasons for why it's smart to be concerned with having a power-pulse timed near it's peak during the production of the ign.spark ! ...
__ The least realized reason has to do with more efficient handling of all the power-juice produced by the alternator, so as to minimize wasted power that's circuited through the battery (by rather having that power made available when the ign.system can make better use of it).
It should be understood that the battery does-not store-up electrical-power from the charging-system like a condenser-capacitor is able to do, since a std.battery is much less efficient because it rather behaves much like a 'load' as it allows more power-juice to actually pass-through itself (to become wasted to ground) than the lesser amount of juice that's actually effectively retained and temporarily stored within the battery itself ! _ So when a pulse of alt.power happens to enter the battery (at a time when the ign.system is-not drawing power),, then only a relatively-small percentage of that power-pulse is kept stored, whilst the rest of it is actually wasted through-to ground.
However otherwise, whenever the ign.system consumes system-power at the same-time (as when a power-pulse is occurring),, then, any alt.produced power-juice that might be left-over to enter the battery, can then enjoy an improved power-storage to power-waste ratio (cuz the battery can better handle & retain larger-percentages of the resulting reduced current-flow passing-through it [as the ign.system is then drawing-away & consuming alt.power as the greater-demanding load]) ! _ And-so the alternator's produced power is thus-then better-handled for improved efficiency (with less alt.power being wasted through the battery [since that otherwise wasted power is then rather being consumed by the ign.system instead]) !
And besides that (most overlooked) saved loss, there's also the fact that the battery's own stored-up power-juice is then not taxed-away as greatly (during the timed power-pulse [that's set to occur whenever the ign.system is then drawing power]) !
So it really ought-to be fairly apparent that such doubled-up power-savings combined-together, certainly totals-up & amounts to rather quite more efficient handling of the alternators produced power ! - (Or actually, that is to say,, one power-pulse of it, per ign.spark.)
Of-course if a std.battery actually stored every fraction of a Coulomb* of power-juice that's fed into it, (like a condenser does),, THEN the above reasoning would be pretty-much reduced to near total insignificance. _ As in THAT (UNrealistic)- case,, there'd then be pretty-much an even-exchange of power-juice in-to & out-of the battery, fairly regardless of the time-span/difference between those two power-flowing occurrences,
(just as most-everyone incorrectly-assumes a battery must naturally do).
(*A 'coulomb' is the number of electrons within a 1-amp.current flowing for 1-second, [which is over 60-billion,billion electrons, I think].)
__ The next most realized reason for preferring to have a power-pulse timed-together with battery-powered ign.timing, is of-course because it certainly at-least assists (if not also significantly intensifies) the strength of the ign.spark,, especially whenever the battery might be a bit run-down ! _ As system power-strength of-course varies from merely the battery's voltage-level alone, up-to the greater system-strength occurring whenever the alternator happens to be contributing one of it's pulses of power.
__ And the most appreciated reason for having the alt.rotor set properly 'timed' for ign.system-empowerment, is so that the engine (and even the entire electrical-system) can then be kept running even if the battery is completely taken off-line ! _ Thus allowing a push-start to get-going, (whereas without the rotor being sufficiently timed,, you'd then have-to get the battery back-up into minimum working-order, to become able to continue on your way !).



" The flywheel position may also play a role with respect to the inertial balance, "

____ That sounds like an interesting detail, (which ought-to be of extra concern to those who run 'total-loss' and remove the rotor/flywheel) !
__ Would you care to elaborate on how such balancing might possibly could be possible ?




____ Concerning the list of factory rotor-angles (below), it's always been a mystery to me as to why Ducati didn't choose & stick-with a single rotor-face marking which was always placed in the same logically located position, (whatever the location logic might've been chosen to actually be).
__ Taking for example the three different settings listed for the Motocross/Mark-III models,, it leaves me wondering whether Ducati had actually repeatedly re-evaluated exactly where the mag.rotor's magnetic-field ought-to be best oriented at (with respect to the [unchanged] factory-recommended ign.timing), or if they rather simply had to deal with large production-runs which had mistakenly had the rotor-marking misdirected somehow in error (and-so consequently dealt with their error-issue as has become presented within their adjusted factory-listings).
In any case, it's-all unduly overly COMPLEXified, as there really shouldn't be any actual/normal need for such screwed-up complication !


Dukaddy-DUKEs,
DCT-Bob

[DewCatTea-Bob]

____ I've wanted to put-together a post such as this ever-since I first read the Lucas-pages posted by Rick,, but that intention originally got put-off back when I beforehand discovered a newer posting posted by Rick that was rather more pertinent to get a reply-post submitted in response-to instead, and-so this-posting has ever-since remained delayed due-to lost incentive. _ But since there's been no further distraction, I'm now getting-around back-to finally submitting a good-bit of this so I can now develop renewed incentive to get it all done.

This special ignition coil employs a
closed iron circuit and has a primary winding whose
impedance is closely matched to that of the ignition
generating coils of the alternator.

____ This is the first I've seen of another source (other than myself) which indicates that the 'impedance' of the ign.coil's primary-winding ought-to be 'matched' with that of the mag.power-coil which is meant to power-up it's associated ign.coil.
In another recent thread,, the functional-usability of a non-stock ign.coil was called into question (as it didn't provide the expected spark-intensity), and-so I had indicated that there was the probable chance that it's impedance was-not as well matched to Ducati's ign.power-coil as the stock Green-label ign.coil must be. _ So It's appreciated that another authority on such matters confirms that impedance-matching is a fairly important issue to take into consideration. _ Cuz only when the impedance of the two coils are exactly equal, can there then be FULL transfer of the available power from the power-coil to the ign.coil ! _ (That's the very-same concern as to why 8-ohm speakers must be connected to audio-amplifiers which have been designed to work with speakers of that [most common] impedance-rating !)
If the impedance of the ign.coil-primary is lower than the impedance of the power-coil feeding it, then the majority of the generated power will rather drop-across the power-coil itself (instead of the ign.coil),, which results with less than max.power-transfer to the ign.coil, and overheating of the power-coil (as IT-itself thus-then becomes the greater load of the series circuit).
And conversely, if the impedance of the ign.coil-primary is higher than that of the power-coil, then while the majority of the flowing power is rather dropped-across the ign.coil-primary (and the power-coil thusly runs cooler), the maximum-power that's otherwise available from the power-coil, is then never developed for full possible use !
So-thus only when the two impedances are matched, is max.available-power then created AND circulated & dropped-across both coils equally, and therefore fully-efficient !
__ To help determine whether an ign.coil's primary-winding is matchable to the power-coil's winding, a finely-graduated ohm-measurement of the two windings would indicate whether their resistance-levels are comparable. _ However that wouldn't necessarily confirm that their 'impedance' levels are closely matched, as it's fairly possible that the two coil-windings don't share the very-same number of loop-turns (which certainly affects the level of impedance). _ But if the number of loop-turns are the same and the resistance-levels of the two windings are also equal, then it can be accepted that they're indeed 'matched'.

When the contact-breaker contacts close, the
primary winding of the ignition coil is short-circuited
and, at the same time, the stator ignition windings
form a closed circuit.

____ While that statement doesn't state anything that's outwardly wrong, it seems that the chosen wording was hastily typed-up and left unedited,, as it would've been more correct & sensible to have rather stated that the "stator ignition windings" is short-circuited, (while rather the ign.coil's "primary winding" is a closed circuit).
__ It's not my intent to nit-pick at their apparently unedited wording, but rather just to clear-up conceptions for any readers who don't already happen to realize what the writer had probably actually meant.

As the magnetic rotor turns,
voltages are induced in the stator coils resulting in
alternating currents while the contacts are closed.

____ Highly disappointing is that even by those tech.writers who really ought-to have been trained better, is that that statement contains an overly common and quite blatant misuse of the term "voltages" ! ... While it would've been fair to have rather stated 'potential' -(actually meaning 'potential-voltage'),, clearly whenever "the contact-points are closed", there can then be NO "voltages" developed at-all ! _ As a direct short-circuit (which the contacts are intended to provide when closed), can-not allow any measurable 'voltage' to build-up whatsoever (since it's potential to exist is being bled-away before it gets any chance to amount to any measurable v.pressure) !! _ So clearly that (poorly) chosen wording is certainly in error !
And-so it's no-wonder that so much of the general-populous so commonly misuse the word 'voltage' so generically whenever referring to most-anything concerning electrical-juice, since even elect.tech-types so generally mouth-out that word-term so loosely without thinking ! _ And because of that lack of proper use over the decades past, it's become as if 'voltage' has taken-on additional (slang) definition,, which is really too-bad, cuz the slang-use often leads to disconcerting confusion amongst those who really don't know any better !
__ What is fairly correct about that statement, is that "currents" do indeed result while the contacts are closed ! _ And the short-circuit through the contact-points insures that maximum current is allowed,, so that when the points open, that established current is then detoured through the ign.coil-primary where it will then produce the maximum possible voltage across the primary-resistance (and the power-winding as well).

When the contacts open, a pulse of 'electromagnetic-
energy (developed in the stator while the contacts
are closed) is discharged through the ignition coil
primary winding.

____ That statement seems to indicate that the very-same 'electromagnetic-energy' which comes into existence within the power-coil's winding next-then becomes discharged into the ign.coil,, and while that's indeed true with the electro.aspect of the electromagnetic-pulse, the magnetic-aspect naturally remains confined within the stator-winding and it's collapsing-field is what's actually depended-upon to force just the resulting electrical-juice to transfer-out & circulate-through the ign.coil.

The effect of this energy pulse in
the primary winding is to induce a high tension
voltage in the ignition coil secondary winding

____ Of interest in that statement is the seemingly needless use of both word-terms "tension" AND "voltage" , many users of the term 'voltage' use & abuse the voltage-word exactly the same as if it's meant-to mean the very same aspect as 'tension' is actually meant to specify. _ However in actuality,, while 'tension' means electrical-pressure, 'voltage' is rather supposed to only be in reference to just an amount of the electrical-tension/pressure,, similarly as air-pressure compares to 'poundage' (as tension compares to voltage).
So realizing such distinguishing detail, their chosen wording is actually not really so seemingly senselessly redundant.

although the optimum magnetic
position is just past the Magnetic Neutral at 300
rev/min,

____ The reason for why the best ign.timing/spark-intensity is attained "just past" peak rotor/stator-alignment & max.magnetic-induction, is because it's better to have the entire brow-top of the power-pulse (that's rather including both sides of the waveform-peak's summit-crest) to help maximally build-up the power-coil's own flux-field, for a fuller charge*,, instead of only utilizing merely-just the side preceding the center-point of the pulse-peak's apex.
So-thus there's that obvious delay (after max.peak-alignment has occurred) which accordingly provides the highest ign.spark-intensity.
__ That circumstance has to do with the minor offset location of the yellow-line -(the suggested TDC.aligned timing-mark [for the 18-degree AAU.systems], seen in the picture of an actual mag.rotor), being rather positioned 2.5 rotor-degrees offset away from the green-line (which is 22.5-degrees away from the blue-line that obviously represents the max.peak-alignment point). _ Cuz having the contact-points closed longer during the extra-5 waveform-degrees, then accordingly allows the current-force within the power-coil to further intensify just a tad-bit longer, so as to then better finish building-up it's strongest possible flux-field (for forcing the greatest possible established-current next-then diverted from ground and rather detoured through the ign.coil-primary),, thusly provoking most intensified ign.spark !
(* A coil becomes effectively-charged because when current is flowing within it, then a corresponding flux-field is concurrently developed around it that's proportionate to the amperage of the current,, and these two 'electromagnetic' aspects are pretty-much locked-together as one, so that when there's any instant-change in the circuit-resistance, the established current-amperage still can't change from what it's been until it's established flux-field collapses accordingly ! _ So-thus when the contact-points open,, then the maximum possible amperage that's been established by the previous 'short-circuit' through the points to ground, is then left no choice but to be FORCED rather through the ign.coil-primary instead. _ And because the established flux-field around the power-coil is already intensified in direct relation to the pre-established max.current-amperage, then when that current-flow is suddenly impeded by the relatively much increased resistance of the ign.coil-primary, the established flux-field (of the power-coil) will not allow the current-flow's amperage to drop-off (instantly at that very point), and-so a high-voltage is right-then developed across the ign.coil-primary, (thusly causing a 'high-tension' voltage within the secondary) !
So-therefore it's helpfully beneficial to take every such advantage to allow the power-coil flux-field to build-up and become fully-established as strongly as possible, (by allowing the mag.rotor-rotation to slightly surpass the center-point of max.peak-alignment [for tiptop magnetic-transfer], by 2 ~ 4 rotor-degrees further-onward just before the contact-points are set to open).)
____ All this reasoning has to do with the explanation for why the Lucas-graft indicates that max.spark-intensity is attainable rather slightly-after tip-top magnetic-transfer has been reached.

it changes to several degrees past at 2,000
rev/min, due to distortion of the magnetic flux.

____ That blaming of "distortion" of the mag.flux-field for the further & further retarded point at which max.voltage ign.spark is best attained,, is due-to the fact that such higher frequencies increase the strength of the effect of 'impedance', which tends to retard the rise & fall of the otherwise normally shaped sine-wave current-waveform.




____ If the small print posted under the pix is found to be too difficult to read,, then drag & drop it to a WordPad-page, or use your PC's magnifier-function (as I-myself prefer to do).


Enlightening-Cheers,
Dct.Bob


UPDATE ! ... While looking-over my post here, I realized an error carried-over from the old thread (previously referred-to), and have now added a correction ! _ The error has to do with the combo.picture (that's currently still left posted where it's been), and the error in question has been corrected within the new replacement picture now seen on top of the first two.
(Later, [after I've had clear enough mind to confirm that the suspect-error is indeed in actual error], I then intend to delete yesterday's posted combo-pic [along-with it's yellow-line positional-error] ).