Identifying Alternator/Magneto

[narrow_monza]

I'm trying to figure out what type of alternator/magneto is in my engine. It appears that the rotor part is engraved with the following part number:

31.20.92

Is it possible to identify it from rotor alone? Or do I have to remove it to check the stator?

Thanks

-Adrian

[wcorey]

I could be mistaken but I believe that's a (brass) 4 pole rotor with the 'pair of dual sided coils' type stator. 25 watts maybe...?
One coil is for the ignition, the other for everything else.
I'm more than certain someone else here will know for sure.

[narrow_monza]

I ended up removing the rotor. The stator appears to have 2 coils so I assume this is the 40W magneto (see attached photo).
But here's what's puzzling. According to the literature, there's supposed to be a 3-pole cable coming out. Well, mine only has a 2-pole cable coming out.
Has this system been modified?

Thanks

-Adrian

[DewCatTea-Bob]

____ I'm considerably perplexed, cuz I'm at a really big loss to come-up with whatever's the actual reason for why I've never before noticed this thread !! _ (I happened to notice it now, as I was just looking for another related thread.)
I'm quite fairly upset that I've somehow missed ever seeing this thread-topic before ! _ And the only way I think it could've happened, is if it's topic-title was since changed after it had become displaced off-from the 1st.forum-page. _ Cuz that's the ONLY-way it seems probable for me to have possibly bypassed taking-note of any posted-thread.
__ This thread-post much interests me,, and-so I'd still very-much like to know where things now currently stand, concerning it's related content.
So anyhow.......



[quote= narrow_monza ...
" The stator appears to have 2 coils so I assume this is the 40W magneto (see attached photo). "

____ Just concerning all 160/250-models only,, the 2-coil/4-pole alt.mag-stators have two main designations... the '40-watt' and the '28-watt' model-versions.
Although those indicated wattages are but MERE general-ratings figured by the factory, and really can't be counted-upon to specifically produce the claimed wattage-amounts outside of a fairly narrow RPM-range (which Ducati figured would likely be an averagely ridden RPM) ! ...
__ It ought be already well understood (by anyone with any basic electrical-education) that any such alternator certainly-can't make any power at-all, whenever it's mag.rotor is-not spinning,, and-also that the faster it spins, the greater thus-then becomes it's power capability. _ So-thus we all ought-to realize that such claimed wattage/power-ratings are merely-just that - factory-claimed RATINGs ! _ And-so therefore, we all ought-to expect such alternators to produce amounts of power that may be less or even more than the stated factory-rating, (depending on RPM) !
Bottom-line here, is that factory power-ratings OUGHT-TO be stated suchly as-like: '40-watts @ 4500-RPM', or whatever the like.
__ In addition, Ducati produced three different versions of the so-called '40w' 4-pole alt.model (for 250-models)... Those three alt.units are... the original twin-wire Monza-type*; the original 2-wire Motocross-type; & the 3-wire Motocross/Mark-III-type.
(* This particular alt.model stands-out from all the other 4-pole alt.versions because, IT's two power-coils are-not independently-separate [like those of all the other 4-pole alt.stators] !) ... As the Monza-type alt.power-windings employ Ducati's rather special ["mutual-induction"] interactive dual-windings method across BOTH power-coils together !)
__ There were also 2 or 3 other 4-pole alternators made by Ducati & CEV, for 200 & 175 models, (of which I'm not so very personally familiar with).



" According to the literature, there's supposed to be a 3-pole cable coming out. Well, mine only has a 2-pole cable coming out. "

____ If it's still stock,, then it could most-likely be either the early-Monza/4-pole type alt.stator (with two YELLOW wire-leads), or an early-Motocross/Mark-III version (with one RED & one YELLOW, wire-leads).



" Has this system been modified? "

____ Could you please re-post your picture ?
__ Even if it no-longer matters to you, it will at-least much interest ME (and perhaps others as well).


Hopeful-Cheers,
DCT-Bob

[narrow_monza]

____ I'm considerably perplexed, cuz I'm at a really big loss to come-up with whatever's the actual reason for why I've never before noticed this thread !! _ (I happened to notice it now, as I was just looking for another related thread.)
I'm quite fairly upset that I've somehow missed ever seeing this thread-topic before ! _ And the only way I think it could've happened, is if it's topic-title was since changed after it had become displaced off-from the 1st.forum-page. _ Cuz that's the ONLY-way it seems probable for me to have possibly bypassed taking-note of any posted-thread.
__ This thread-post much interests me,, and-so I'd still very-much like to know where things now currently stand, concerning it's related content.
So anyhow.......



[quote= narrow_monza ...
" The stator appears to have 2 coils so I assume this is the 40W magneto (see attached photo). "

____ Just concerning all 160/250-models only,, the 2-coil/4-pole alt.mag-stators have two main designations... the '40-watt' and the '28-watt' model-versions.
Although those indicated wattages are but MERE general-ratings figured by the factory, and really can't be counted-upon to specifically produce the claimed wattage-amounts outside of a fairly narrow RPM-range (which Ducati figured would likely be an averagely ridden RPM) ! ...
__ It ought be already well understood (by anyone with any basic electrical-education) that any such alternator certainly-can't make any power at-all, whenever it's mag.rotor is-not spinning,, and-also that the faster it spins, the greater thus-then becomes it's power capability. _ So-thus we all ought-to realize that such claimed wattage/power-ratings are merely-just that - factory-claimed RATINGs ! _ And-so therefore, we all ought-to expect such alternators to produce amounts of power that may be less or even more than the stated factory-rating, (depending on RPM) !
Bottom-line here, is that factory power-ratings OUGHT-TO be stated suchly as-like: '40-watts @ 4500-RPM', or whatever the like.
__ In addition, Ducati produced three different versions of the so-called '40w' 4-pole alt.model (for 250-models)... Those three alt.units are... the original twin-wire Monza-type*; the original 2-wire Motocross-type; & the 3-wire Motocross/Mark-III-type.
(* This particular alt.model stands-out from all the other 4-pole alt.versions because, IT's two power-coils are-not independently-separate [like those of all the other 4-pole alt.stators] !) ... As the Monza-type alt.power-windings employ Ducati's rather special ["mutual-induction"] interactive dual-windings method across BOTH power-coils together !)
__ There were also 2 or 3 other 4-pole alternators made by Ducati & CEV, for 200 & 175 models, (of which I'm not so very personally familiar with).



" According to the literature, there's supposed to be a 3-pole cable coming out. Well, mine only has a 2-pole cable coming out. "

____ If it's still stock,, then it could most-likely be either the early-Monza/4-pole type alt.stator (with two YELLOW wire-leads), or an early-Motocross/Mark-III version (with one RED & one YELLOW, wire-leads).



" Has this system been modified? "

____ Could you please re-post your picture ?
__ Even if it no-longer matters to YOU, it will at-least much interest ME (and perhaps maybe others as well).


Hopeful-Cheers,
DCT-Bob

Hi Bob,

I got distracted for a few months and now I'm back.
Here's an annotated photo of the stator. There are 2 coils. Coil A has one end soldered to chassis where both wires exit the winding.
Coil B has one end soldered to chassis at the opposite end of the winding.
Does that mean Coil A is to power the ignition and Coil B is to power the lights?

Thanks

-Adrian

[DewCatTea-Bob]

[quote= narrow_monza ...
" Here's an annotated photo of the stator. "
" Has this system been modified? "

____ I'd say yes, probably so,, as far as that pair of lead-wires are concerned, as I know of no stator which came with a white-wire & a black-wire !
The stator-model seems to be the original 2-wire 40-watt model which was employed on the early Motocross & Mark-III models.
The wire-lead for the ign.system should be YELLOW, and the wire-lead for the lights should be RED.



" There are 2 coils.
Does that mean Coil A is to power the ignition and Coil B is to power the lights? "

____ It appears that you have that correct,, as the power-coil meant for the ign.system has a thinner gauge of coil-winding, while the lighting-coil has the thicker-gauged winding.
__ While many (who know no-better) have often mixed-up that stock wiring-arrangement and found little difference in functional-operation, the result causes the lighting-coil to overheat (as it powers the mostly short-circuited ign.system) and it's insulation-coating soon becomes dark-brown (as the rather clear-coating gets burned-up), which eventually leads-to coating-deterioration with resulted possible shorts within the coil.
(This fairly common happenstance has been getting put-to-the-test by [apparently doubtful] Jim-himself, with his daily-rider -(Mark-III),, as he has rather purposely swap-wired his lighting-coil to the ign.points [against my advice] ).
____ Are you intending to run your (250 Motocross ?) Duke with it's electrical-system kept just as originally-stock ?


Duke-Cheers,
-Bob

[narrow_monza]

[quote= narrow_monza ...

" There are 2 coils.
Does that mean Coil A is to power the ignition and Coil B is to power the lights? "

____ It appears that you have that correct,, as the power-coil meant for the ign.system has a thinner gauge of coil-winding, while the lighting-coil has the thicker-gauged winding.

**** I can't seem to visually tell the difference between the gauges of the coil-winding.
It appears like Coil A is bulkier than Coil B, but maybe that's because it has a higher number of windings?

__ While many (who know no-better) have often mixed-up that stock wiring-arrangement and found little difference in functional-operation, the result causes the lighting-coil to overheat (as it powers the mostly short-circuited ign.system) and it's insulation-coating soon becomes dark-brown (as the rather clear-coating gets burned-up), which eventually leads-to coating-deterioration with resulted possible shorts within the coil.
(This fairly common happenstance has been getting put-to-the-test by [apparently doubtful] Jim-himself, with his daily-rider -(Mark-III),, as he has rather purposely swap-wired his lighting-coil to the ign.points [against my advice] ).

**** I'm going to assume Coil A (bulkier) is meant for the ignition system.

____ Are you intending to run your (250 Motocross ?) Duke with it's electrical-system kept just as originally-stock ?


Duke-Cheers,
-Bob

**** The bike is has a 250 Scrambler engine on a street frame. The wiring does not exist so I'm starting from scratch. My plan is to go with a very simple 6V no-battery wiring just to get it running. I don't plan on riding it at night time. Any suggestions on a simple 6V wiring that could make use of this stator would be greatly appreciated.

Thanks

-Adrian

[DewCatTea-Bob]

[quote= narrow_monza ...
" **** The bike is has a 250 Scrambler engine on a street frame. The wiring does not exist so I'm starting from scratch.

____ Then the wiring of the motor will pretty-much dictate the wiring you'll need on your street-bike frame.



" My plan is to go with a very simple 6V no-battery wiring just to get it running. "

____ Then you'll possibly wish to employ the simple 2-wire alt.stator electrical-system of the early Motocross/Mark-III & 450RT, (which have no preset means for a brake-light).
__ Here's a link to a fairly closely related post which concerns that simplest wiring-scheme of such AC.powered Duke-models. - viewtopic.php?f=3&t=442&start=20#p12517



" Any suggestions on a simple 6V wiring that could make use of this stator would be greatly appreciated. "

____ Something you ought-to consider while you still have the alt.stator readily exposed for possible modification, is to replace the two wire-lead alt.cable with a wire-cable that has TWO-pairs* within. _ That way you'd then already be set-up to adapt any kind of system in the future, without having-to pull the flywheel back off again (to make whatever required connection-changes associated with whatever system you may wish to adapt to).
(* Many chose to install a prefabricated appliance cable which has 1-black & 1-white & 1-green & 1-red 16-gauge wire-leads contained within.)


Duke-Cheers,
-Bob

[narrow_monza]

Going back to the Workshop Manual, the diagram depicting the simple 2-coil flywheel-magneto of the Mark3 (attached) shows that the ignition coil is actually the one with the one wire tied to chassis at the other end of the winding (bottom coil, or Coil B in my photo).

[DewCatTea-Bob]

____ Firstly, thanks for your contributed pic.drawing of Ducati's THREE/3-wire '40-watt' alt/mag.stator !


[quote= narrow_monza ...
" the diagram depicting the simple 2-coil flywheel-magneto of the Mark3 (attached) shows that the ignition coil is actually the one with the one wire tied to chassis at the other end of the winding (bottom coil, "

____ What leads you to think that ?
It seems you may've mistook my specific wording... Cuz when I used the word "simple", I was in regards to the EARLY electrical-SYSTEM, (not just the associated early 2-coil stator with BOTH power-coils grounded) !
The particular stator-diagram which you've posted, is only intended for the rather later n-c.Mark-III/3 & pre-1966 5-speed Scrambler models, (which have a concocted brake-light circuit adapted), and-so therefore is-NOT the 'simple' version ! ...
__ The upper-located power-coil has TWO wire-leads,, a YELLOW-wire for direct-connection to the ign.system, AND-also a WHITE-wire added for direct-connection to it's intended brake-light circuit (& ground) !
While the "bottom coil" is still left grounded since it's still intended to power the lights, (same as with the early-version) !
__ The energy-transfer (magneto-like) ign.system depends on a higher-tension burst of energy to suddenly excite the ign.coil (for a higher resulted spark-voltage), and-so it's power-coil employs more turns of a thinner gauged winding.
While the higher current-demand of the lighting-filaments rather depend on a higher current to tension ratio, and-so thus the power-coil meant for the lighting-circuit rather employs less turns of a thicker gauged winding !
SO, you can count the number of coil-turns on each power-coil, to then tell & be-sure of which is ACTUALLY which !


Hopeful-Cheers,
-Bob