Ducati's FIRST 4-pole Alternator Rated at 40-watts

[DewCatTea-Bob]

____ I'd like to confer with the buyer of the following eBay-item concerning his intentions with the stator. - http://www.ebay.com/itm/311154913773?ru ... 26_rdc%3D1
__ I believe this was the first stator-type which was constructed by Ducati-themselves and first employed on their later 200-models. _ And although it was rated by Ducati for 40-watts, it's definitely not the same stator-model as the later-designed example that's far-more well-known and commonly referred-to as The '40-watt' model ! _ As that newer-type '40w.model' rather has two separate & independent power-coil windings - (one coil-winding primarily for the ign.system and the other coil-winding just for the main-lights only), which is why I've chosen to refer to it as an 'alternator/magneto-stator' -(or "alt/mag.stator"). _ While the older 40w.version has a pair of windings spread-over a matched-pair of power-coils !
So instead of having separate windings on each of the two power-coils, the older 40w.version rather has both pairs of it's windings spread-over both power-coils. _ And the reason for that somewhat odd (dual) winding-arrangement, is so that the two matched power-windings may thus-then mutually induce power directly into one-another (independently of the power originally induced by the rotor-magnets) when duel half-wave rectified and whilst feeding a load. ...
When there's no load, then of-course there's no current flowing through either winding to induce power into each-other and-thus no 'mutual-induction' then takes place. _ But as the load-system draws more & more current, the desired mutual-induction effect accordingly increases, (which thus-then provides additional induced-power adding-up to more than just that which comes from the action of the spinning mag.rotor alone !). _ So this clever working-action makes Ducati's unique alternator somewhat self-regulating (in that it doesn't produce higher amounts of power unless the load system happens to be consuming higher amounts), as the mutual-induction effect attempts to exactly match the same amount of power as is being consumed. _ So of-course this exceptional setup is capable of producing at-least as much max.power as an otherwise equivalent full-wave rectified stator (which can't self-regulate).
__ But then comes-up the question of why isn't everyone always well satisfied with the power-output of Ducati's alternator !?
Well if they always rode at very-high RPM, then they would indeed always be completely satisfied,, cuz then the mag.rotor induced power would be strong enough to begin with for there to then be more than sufficient mutually-induced power to supplement the power consumed by the load. _ But of-course everyone doesn't run at racing RPM speed most of the time. ...
Unfortunately however, many wish to run powerful headlights whilst riding at low-RPM in the city,, and while the mutual-induction itself would naturally tend to match the current-draw of the high-power headlight, the shortfall comes from the fact that at low-RPM, the rotor-magnets then don't induce enough power into the coil-windings (to at-least HALF-satisfy the load-demand) to begin with ! _ So that thus leaves insufficient power for the load to consume which thusly in-turn leaves accordingly reduced mutual-induction effect to fill-up the power-gap (difference between load-demand & charging-system supply).
__ That's why I've always criticized Ducati for merely half-wave rectifying instead of full-wave rectifying,, as full-wave rectification provides double the power initially to begin-with (regardless of load current-consumption), for best-possible satisfaction of the load-demand near lower-RPMs. _ And that FULLER supply of low-RPM power-output can possibly provide about a 25% power-advantage down-within the low-RPM.range where it's much more apt to be needed (than having some trick-added power-advantage fully operating at higher-RPMs where any increasable power availability is then not really needed anyhow).
Ducati finally realized this more advantageous circumstance in 1976 when they then finally gave-in & updated their 860's 150w dual half-wave rectification charging-system to the 200w full-wave rectification system.
____ I may likely come-back with still more related-stuff concerning this topic, but I've already strayed-off way-more than I had originally meant to include here within this first-post when I first decided to bother with posting this new-thread. _ So I'm going-to quit this now, (for the-time-being).

____ BTW, I'm hoping that Hans/ducwiz has finally come to understand exactly what I've meant in the past whenever I've previously stated "pull/pull" in regards to 'mutual-induction',, and will either confirm that such is indeed inevitable, or offer his-own explanation as to WHY he may still think that such beneficial winding-induction interaction is possibly non-existent.
__ And Hans, this-thread would be more suited for any further discussion of that rare/odd old non-Ducati 175/200 alt.stator (which you've previously mentioned-of within another thread last month).


Enlightening-Cheers,
D.Bob

[Rick]

I didn't buy the Ebay parts, but I have a couple of the same rotor/stator pairs. If you're interested in resistance values of the 2 windings, they are:
Stator #1:
Left terminal board solder pad to right terminal solder pad: 0.650Ω
Left terminal board solder pad to solder blob on 2 wires at right: 0.281Ω
Right terminal board solder pad to solder blob on 2 wires at right: 0.376Ω
Stator #2:
Left terminal board solder pad to right terminal solder pad: 0.620Ω
Left terminal board solder pad to solder blob on 2 wires at right: 0.265Ω
Right terminal board solder pad to solder blob on 2 wires at right: 0.372Ω

stators.jpg

I didn't scrape down to a fresh surface on the solder, so some dirt and oil probably accounts for the sums being off.
I'll attach a photo of my measurement setup- sometimes knowing how a measurement was taken is as important as the value itself.
The power supply is setup as a constant current source of 1 amp, so Ohm's law reduces to: resistance=volts. I clip the 1amp leads directly to my multimeter probes, and the voltage indicated on the meter is equal to resistance. If I remember right, this setup works because the input resistance of the multimeter is so huge that practically all the current flows into the probes and through the windings.

current source.jpg

Rick

[DewCatTea-Bob]

[quote= Rick ... " I have a couple of the same rotor/stator pairs. "

____ Wow Rick, thanks for your impressive related post !
__ Do you know for-sure what Duke-models your two stators came from ? _ And do they both state 'DUCATI' on their stator-plates ?



" I didn't buy the Ebay parts "

____ Of-course that's of no concern. _ As I was merely hopeful that the actual buyer just happens to be one of our fairly active fellow-members.



" Stator #1:
Left terminal board solder pad to right terminal solder pad: 0.650Ω
Stator #2:
Left terminal board solder pad to right terminal solder pad: 0.620Ω "

____ That the darkened -(slightly burnt from heat) power-coils (of 'Stator #2') have resulted with slightly reduced resistance-levels, (as the insulation-coating has thusly accordingly deteriorated), is to be expected.



" Left terminal board solder pad to solder blob on 2 wires at right: 0.281Ω
Right terminal board solder pad to solder blob on 2 wires at right: 0.376Ω "

____ While I don't greatly suspect the validity of these quite notably different ohmic-values,, I do find their inconsistent resistance levels to be somewhat disconcerting, as I believe the two separate windings really ought-to be 'matched' ! ...
__ The shown left-side power-coil (of Stator #1) appears to be slightly fatter (than it's right-side located partner), so perhaps Ducati meticulously planned for the primary-winding -(the one that's meant to be in time [phase wise] with the production of the ign.spark) to have a slight advantage. _ I don't really know,, but since the system is supposed to include a battery, I-myself think that the two windings should be rather exactly matched (to at-least the .01 decimal level) and-thus each be nearer to the .325-ohm average-level.
__ Conversely, the right-side power-coil of 'Stator #2' is the one which seems to appear to be the fatter partner. _ So if I happen to be correct about one actually being meticulously planned as the primary-winding,, then the mag.rotors of the two so differing stators, must have their timing-marks placed near opposite poles ! _ In other-words, while one rotor has it's timing-mark near a N.pole, the other rotor must accordingly have it's timing-mark near a S.pole. _ This alternated arrangement is so that the power-pulse which happens to spark the ignition will be of the positive-phase that the connected half-wave rectifier allows to enter the charging-system.
(If I'm wrong about the two partnered power-coils actually being of differing dia.sizes, then this very-last paragraph [within this main-paragraph] is all wasted conjecture, [but it would collaborate the noted difference in winding resistance-readings].)




" The power supply is setup as a constant current source of 1 amp, so Ohm's law reduces to: resistance=volts. "

____ That's pretty-handy how that works to come-out that way ! _ But just have-to depend on the power-supply to always maintain a constant current-flow of exactly 1.000-amp in order for the deduced resistance-figures to be so fully trustworthy.



" this setup works because the input resistance of the multimeter is so huge that practically all the current flows into the probes and through the windings. "

____ Indeed so ! _ As the resistance-differences of the two possible circuits connected in parallel,, is so VASTLY-extreme, that the volt-meter is pretty-much entirely out of the loop ! _ So it's contributing effect on the sought final-result, is considered to be non-existent.


Enlightened-Cheers,
-Bob

[Rick]

Yes, both backing plates are the same casting:

stator back face.jpg

One was from an Elite- don't know what model the other was from.
Rick

[DewCatTea-Bob]

[quote= Rick ...
" both backing plates are the same casting: "

____ I thought they probably would be, since their design is so similar (unlike the original CEV-made stators).



" One was from an Elite- don't know what model the other was from. "

____ The two do seem to appear to be from different models, (one, more likely from a considerably newer 250-Monza),, as one seems purposely updated from the other. ...
__ Have you noted my (possibly worthless) observation concerning the possibly varied dia.size of the partnered power-coils of each of your presented stators ?
I'm hoping you still have both of the original mag.rotors of both stators kept separately identified, so that you can test them for any polarity discrepancy which they may possibly have in regards to the general location particularly chosen by Ducati for the 'timing-mark' (placed on their front-faces).
As it seems that there may indeed be possible (& rather meticulous) reasoning for the two separate power-windings to have been purposely slightly mismatched by Ducati.


____ I've included a combo-pic of Hans's possible CEV-made stator from an older 200 (or 175).


Curious-Cheers,
-Bob

[Rick]

the wire diameter seems to be the same on both coils, but it's possible that the visible, outside layer on both coils is covering up an interior wire of a different gage- I'd need to unwind it to find out- the varnish on the wire makes it hard to figure out the winding scheme as I can't get a probe onto bare wire.
The diameter of the wound coils is about the same, not the difference I see on other stators, with one coil considerably larger than the other.
I've got more drawings of the rotors and the phasing marks stamped into them- will find them and send them along.
One of the stators was with a 31.20.92 rotor, but I got careless with the other one, and now I'm not sure which rotor it came with- maybe a 31.20.01, and possibly but less likely a 31.20.94- both of those rotors have the phasing mark in a different position relative to the pole pieces.
Rick

[DewCatTea-Bob]

[quote= Rick ...
" the wire diameter seems to be the same on both coils, but it's possible that the visible, outside layer on both coils is covering up an interior wire of a different gage- "

____ I'd much doubt that more than one size of wire-gauge has been used in the coil-windings ! _ I never meant to indicate that as being a possibility,, so if any wording I've stated had led you to try determining that, then I'm sorry for the misleading wording.



" The diameter of the wound coils is about the same, "

____ I used-to be pretty familiar with all the 'DUCATI' 40w.stators and I don't recall having ever noted any difference in power-coil dia.size between the two partnered coils on the Monza-type stators. _ But as I looked at your picture showing your two examples, (for any clue as to why one winding has slightly more resistance than the other), it seems to appear that one coil is fatter than the other (in both stator-examples,, and somewhat oddly, that thin/thick relationship looks to be reversed from one-another between your two presented stator-examples). _ So if in fact, both of the two pairs of power-coils are all actually exactly-identical in diameter-width,, then my perception of otherwise, must be due-to an optical-illusion somehow presented by the picture of your two stators. _ (I wonder if anyone-else also seems to see that size-inconsistency !?)



" not the difference I see on other stators, with one coil considerably larger than the other. "

____ Right, with the alt/mag.stators, their ignition and lighting power-coils are most certainly obviously different in dia.width ! - (Due-to unidentical number of winding loop-turns and wire-gauge sizes.)
__ However I would've expected the (supposedly matched) pair of Monza-type power-coils to consistently always be the very-same dia.width,, but then again, I also would've expected both of their windings to have the very-same resistance-level as well, (within a more reasonable tolerance-range).



" I've got more drawings of the rotors and the phasing marks stamped into them- "

____ You sure are proving to have become a surprise exceptional resource on such stuff as this for the forum-membership, Rick !



" One of the stators was with a 31.20.92 rotor, but I got careless with the other one, and now I'm not sure which rotor it came with- maybe a 31.20.01, and possibly but less likely a 31.20.94- "

____ Due-to the extensive quantity of such varied rotor-numbering, I never learned of any possible significance that those number-designations might've indicated, (but it certainly must indicate more than merely such as a serial-number sequence of-course).



" both of those rotors have the phasing mark in a different position relative to the pole pieces. "

____ That certainly is indicative of having come from different Duke-models, and relatively slight differing in degree-angles may thusly be expected,, however whether the timing-mark happens to be located for setting the mag.rotor for intended activation by a N/S.pole or a S/N.pole arrangement, is possibly a more significant revelation. _ So whether the t.mark happens to be located ahead-of the center-point of a N.pole or a S.pole, could be enlightening.


Enlightened-Cheers,
-Bob