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Expired-Notice! - It's over-due that I reEdit this posting (so that further reading of this thread is not needed in order to realize that I've confirmed that I errored at the time when I wrote this post)! ...
The error was that, (at the time I wrote it) I was drawing on presumption rather than actual-memory...
I was then assuming that the 28watt-alt's white-wirelead was attached to the (left-sided) ign.power-coil, just as the WHITE-wirelead indeed IS, in the case of the 40watt-alt ! - (Yep, the similarity of those two 4-pole alternators has confused me also previously - whenever I've quickly thought about them, after having not done so for a real-long time! - As I do actually recall making the exact same memory-error at least once before [over 2 decades ago]!)
My mistake, I'm sorry I've taken so long to get back to this & correct it!!
I'll leave the original-post as it has been, for a while longer,, before I then go-ahead & correct it's error -(of which power-coil includes the winding that's meant for charging the battery in the 28-watt set-up).
DCT-B

NOW UPDATED! - (One week later than the above Notice.)
Everything written by me in this post, is NOW reEdited to be completely correct!
DCT-Bob



NOTE that this new thread is actually a continuation of another thread which began this subject-topic under the TOPICS-title: " Late narrowcase battery box " .

By kmev: ...
" It sounds like the second system with a fourth wire added is better suited to a modern road bike, and I do indeed need to replace the stator wires. This is not a restoration but a rideable rebuild, so I am not concerned with keeping it to factory specs. At this point I think I'm inclined to go with the 6 volt rather than 12 as this bike will be used around town a lot (hence lower rpms). "


____ First I'll start this new thread by pointing-out that the main problem which is to be addressed in this thread, is to relatively cheaply solve the problem of the dim head-lighting which occurs at low-RPM on the Scrambler & 160 models which employ the (so referred to)- "28-watt" type ALTERNATOR -(often non-correctly referred to as a [complete] 'magneto').
__ I myself have not performed this particular modification since the early '80s but, I've done it a few times for myself and others, and it works well enough to solve the common concern of dim-lighting at lower engine-revs (using just the stock 28w.alt).
This model of alt.stator has just two, completely separate power-coils... The stock right-side power-coil has two winding-leads -(one for the lighting, and it's added winding-lead for keeping the battery charged),, while the left-side power-coil has a winding that's intended for directly running just the ignition only.
It's the lighting/charging power-coil which needs to have an extra wire-lead connected to it's coil-winding lead-end which was originally soldered to the (grounded) stator.
So it's suggested here that ya unsolder that lead-end from the stator, and instead connect it to a 18-gauge wire of another alternate color which won't be used elsewhere, (preferably red & green).
__ Ya should (also) replace the stator's three original wire-leads, (RED for lights; WHITE for charging; YELLOW for ignition), with the same colors of 18ga wires, (removing an old wire-lead and resoldering-in one new wire at a time - so as to avoid any color mix-ups).
I then suggest that you use black or clear fuel-line, (or automotive air-hosing), to use in place of the original black outer-conduit of the stock 3-wire alt.stator-cable.
If the hose-line which you've chosen for your new cable-conduit is just a bit too narrow to push though the 4th wire-lead after the first three have been inserted-through, then you could PULL all 4 wire-leads through it all together at once, by temperarily solding the ends of all 4 wire-leads to just one wire which has already been pushed through (your choice of new conduit-covering), and with some greasy-oil pre-inserted, draw-through your new batch of wire-leads. _ (I've always had to use this method more so than not, whenever making new alt.stator-cables.)
____ Now if one wishes to attempt to go with a 12-volt conversion while retaining this particular (28w) alt.stator model, then it would be best to do the same modification also with the power-coil winding that's intended for the ignition-circuit,, so that it's coil-winding's AC-output can also be full-wave rectified, and thus it's additionally supplied DC-juice will also help to keep the battery's 12-volt charge from falling-off during low-RPM running with lights on!
Indeed this additional power-coil modification could be a worth-while mod even for just the 6-volt set-up, as well. _ However in this case, other ignition-system mods would then of course be required as well !
(I recall starting this '5 wire-lead' stator-modification on a 28w-stator, for a 12-volt project once, but I don't remember ever finishing that alt-mod project.)
____ Because these 4-pole alternators don't ever produce a lot of excess power (for their intened loads), a voltage-regulator of any type should not be required to protect the battery (in this intended case), and the battery itself, (if not too small), acts as a fairly-good voltage-regulator (to protect the lightbulb-filiments from peak-voltage ouputs from the alt.power-coil[s] ), anyhow!

____ So what this intended modified electrical-system will do is use the weak power-winding (that's intended to keep the battery charged), by rectifying it's low-power AC-output and provide a relatively small amount of DC-juice to the battery (preferably only whenever the key-switch is in it's ON-position). _ Plus, ALL the AC-power which the right-side lighting/charging power-coil produces, will be full-wave rectified and shared with the battery (preferably only) when the light-switch is in it's ON-position. - (That's how the superior Japanese-systems work as well as they do!)
__ I really don't recommend trying to use the "28-watt" type alternator for a 12-volt system, mainly because the available 12-volt loads consume a bit more power-juice -(wattage), the main example being the headlight-bulbs [which use 35-watts, vs. 25-watts for a 6-volt version] ).
While I'm quite positive that a 12-volt system is certainly possible, it surely would require somewhat higher-RPM running in order to keep it's 12-volt battery up to par!! - (With lights on, compared to an equivalent 6-volt system.)
(This is true with any such system!)


Bright-Cheers,
DCT-Bob

I'm sure I'll have plenty of questions along the way, but for now here are some images of my 28-watt stator. In the images the wire colors are from left to right: red, white, yellow.

EDIT: 12/26/09 - I rotated the top photo 180 degrees so the stator is oriented the same in both images

Just a FOLLOW-UP.....

____ I've been thinking about stuff related to my previous posting on this thread, and now have more to add...

____ While I've completed and have used my '4-wire' modification of the "28-watt" alternator to solve the dim-headlight problem for the 1966-Scrambler & 160 models, for use with a 6-volt set-up,,
I have never tried this 4th-wire modification (on a 28w-stator) for use with a 12-volt set-up.
Nor have I ever finished the '5-wire' modification of the 28w-stator for actual use with either 6 or 12 volt set-ups. _ However, I'm absolutely positive that the 5wire-mod would be significantly superior to the 4wire-mod (for keeping the battery charged at low-RPM)! _ And while the 5wire-mod may not be really needed for a 6-volt set-up, I wouldn't advise going for a 12-volt set-up without doing the 5wire-mod!
I'd also recommend that the 5wire-mod be used for a 6-volt set-up as well, if a lot of low-RPM riding with lights on is expected to often occur, (especially if ya don't employ a full-sized battery).
__ I have since recalled why I never finished the 5wire-mod of a 28w-alt.stator for my own past project...
I had reached a point with my intended project where I had not yet made-up my mind as to whether or not to stick with just the 5wire-mod, or go-fourth with a '6wire-lead' modification (of the same 28w-stator) and perhaps experiment with various 12-volt set-ups. - (The 6wire-mod allows full-wave rectification of each of the 3 coil-windings, separately & all at once!)
But before I ever had to make-up my mind on that, I acquired a spare 6-pole/4-coil alt.stator (& it's rotor, from a '65-Monza), and so instead modified that alternator for use with a 12-volt system -(to power everything for my intended Scrambler-project).
So I unfortunately never got to do all the experimenting which I had hoped to try-out with that modified 28w alternator on it's intended project. - (Things went that way only because I unexpectedly had a buyer twist-my-arm to finish the project and sell it to him asap! _ And I KNEW for sure then that the 60watt-alt would indeed well run a 12-volt system, like he really wanted!)
__ I was quite positive that the 6wire-mod would work with either a 6 or 12 volt system because I had already converted a couple of old 4-speed Monza-models with their old 4pole-2coil stators -(which are almost identical to the narrow-case SCR-stators), to run 12-volt systems.
____ While thinking about the 5wire-mod, I realized that the full-wave rectified outputs of the two separate coil-windings could be wired-up in series, to then allow fairly good charging of a 12-volt battery even at low-RPM! - (In other words, with the negative-terminal of the 1st FW-rect connected to ground, and it's positive-terminal connected to the negative-terminal of the 2nd FW-rect, and then the positive-terminal of the 2nd FW-rect could be connected to the positive-terminal of a 12-volt battery,, to more certainly keep it charged at low-revs.) _ However, some type of voltage-regulator would likely be needed to control such a modified 28w-alt's combined power-output at high-RPM, if running a 6-volt system.

____ So ya see, there are really quite a number of options which ya could choose from,, using original Ducati alternators !


DUKE-Cheers,
-Bob

Bob

As usual your posts are very interesting.I had an experience a long time ago,riding home from a long ride,with my wife packing double on a 66 sebring.60 watt alt. 50 miles from home at 60mph, the lites were good and brite, and when we got home in the dark.Shut off the motor and every thing was dead after trying to restart motor,the next day I found one of the batt.wires had come off, and it ran good all the way home. Tell me why it ran ok, like that?
Can a 60watt be improved?
I also had a 70 w/case 350 scr. it had a heavier alternator, but it was different from the n/case alternators as how to wire up.I thought it acted like the french excited field alternators. the regulator went bad, and I hooked it up with a finned honda rectifier, but only would charge by running batt current in and then would work fine like that. I've since taken the motor a part and can't remember how I wired it back then Capt Paul

" at 60mph, the lites were good and brite, and when we got home in the dark.Shut off the motor and every thing was dead
I found one of the batt.wires had come off
Tell me why it ran ok, like that? "

____ Sure-thing Paul !
I myself had that exact same occurrence happen on more than one occasion! - (Complete a ride back home after nightfall after a battery-cable had broken-off the battery, while riding a Monza or Sebring!)
While you were running like that, you should've noticed that the head-light was brighter than normal at higher-revs & dimmer than normal at lower-revs!
__ The reason that the engine still ran is because the factory installs the magnet-rotor flywheel so that it is correctly timed to the crankshaft, so that the alternator is getting very close to producing it's peak-output at the same point when the ignition-points are opening (at kick-starting-RPM).
At higher running-RPMs, the ignition-advancer causes the ign.points to open at a sooner point well before peak-power output (by the alternator) is to occur,, however, then it's not as important to have the alternator's peak-power output timed to occur at the same time as when the ign.points fire-up a spark because, the faster an alternator's rotor spins, the more power it has to offer! - (So while the ign.advancer causes the ignition to occur at times when the alternator is further from being able to produce it's peak-power, the alternator also happens to be stronger at those premature times anyhow!)
__ Now that's when the alt.rotor has been correctly 'timed' to the crankshaft! ... Some people pull the flywheel-rotor and then press it back on without correctly setting the 'timing-alignment' before-hand. _ And in such cases as that, the engine may or may not run right, without a battery. - (As the alternator has zero-output just as often as the number of times that it makes it's peak-output !)
It seems that your magnet-rotor was still properly set during that ride you mentioned!


" Can a 60watt be improved? "

____ Yes, the 6pole-4coil "60-watt" alt.stator can be modified so as to make available twice as much juice as that which the stock-system allows the use of.
(I'd prefer to start a separate thread for that subject, if you're interested.)


" I also had a 70 w/case 350 scr. it had a heavier alternator, but it was different from the n/case alternators as how to wire up.I thought it acted like the french excited field alternators. "

____ This reminds me that I once read something like that somewhere back in the late '60s... Seems that somebody noticed the red-wire from the positive-post of the battery went directly (through the reg.rect-box) to the alternator, and thus assumed that the battery's power was needed to "excite" a field within the 'dynomo'. ...
Well by 1972, I came to positively know for sure that that notion was all just pure BS!
That red-wire to the alt.stator is just a center-tap for the dual half-wave rectification-circuit !


" the regulator went bad, and I hooked it up with a finned honda rectifier, but only would charge by running batt current in and then would work fine like that. I've since taken the motor a part and can't remember how I wired it back then "

____ I don't really know what you had going-on there, and without knowing the exact workings of whatever Honda-unit you used,, I just can't comment at all on that.


DUCATIly,
DCT-Bob

" In the first image the wire colors are from left to right, yellow, white, red. "

____ Well kmev, I was hoping that you'd point-out which power-coil (right or left), is the coil which has only 1 wire-lead connected to it, and what that wire's color is. _ (No need to point-out the remainder then.)

____ Were you able to easily see where & how the 3 coil-leads were grounded to the stator-plate? _ If so, do you think you can make the required wire-lead modification(s) okay?


Thanks,
-Bob

DewCatTea-Bob wrote: I was hoping that you'd point-out which power-coil (right or left), is the coil which has only 1 wire-lead connected to it, and what that wire's color is......
____ Were you able to easily see where & how the 3 coil-leads were grounded to the stator-plate?

As I understand this stator, the lighting coil is the copper colored one with the yellow wire attached (the right one in the above images). The other end of the winding is grounded/soldered to coil next to the yellow wire.

The ignition/battery coiI has the red and white wires attached (the left coil). There is also a grounding wire soldered to the coil on the opposite end of the wires.

I cannot find a third coil wire grounded to the stator plate.

As I understand the stator modification, the grounding wire on the right coil (the ground wire next to the yellow wire) is unsoldered and a new lead wire is attached to this wire?

" I cannot find a third coil wire grounded to the stator plate. "

____ Okay, at this point it seems that something's not adding-up right,, so it's good that we're checking to make sure that all is correct before continuing-on.
__ It's been a long time since I've inspected in hand one of the 28-watt stators which still had it's original wire-leads still soldered-in just as stock! _ So it's possible that I've errored concerning which power-coil is the coil that has 2 windings. _ And I no longer have this model of stator where I can get hands-on, currently.
So next I'll list only facts which I'm totally positive about. ...
_ The coil-winding which powers the head & tail lights, originally had a RED-wire soldered to one of it's lead-ends !
_ The coil-winding which charges the battery, originally had a WHITE-wire soldered to one of it's lead-ends !
_ The coil-winding which powers the ignition, originally had a YELLOW-wire soldered to one of it's lead-ends !
_ Concerning the power-coil which has 2 windings,, while EACH winding has a (separate colored) wire-lead soldered to ONE of it's (two) lead-ends, each of those windings has it's other lead-end grounded... And those two grounded lead-ends -(one from each of the 2 windings), are often twisted-together and soldered to a single/common eye-terminal that's grounded by a screw which holds the power-coil's core to the stator-plate.
___ Now if you could look-over everything well (with a magnifying-glass) to reassess what's what, and also confirm which color of wire is directly connected to whichever coil,, then we should be able to go-on from there.


_Bob

DewCatTea-Bob wrote:" Now if you could look-over everything well (with a magnifying-glass) to reassess what's what, and also confirm which color of wire is directly connected to whichever coil,, then we should be able to go-on from there.

I looked everything over more closely and I did find all 6 wire ends:

1) The left (darker) coil has two windings: It has one ground soldered in the upper left of the top photo. One wire is soldered to the red lead, and the white (center) lead has TWO wires soldered to it. They run together without any insulation between them and are joined to a larger terminal end that is soldered to the white wire.

2) The right (copper-colored) coil has one winding: one end is soldered to the coil plate in the lower right of the top photo. The other end of the wire is soldered to the yellow wire.

Keith

" The left (darker) coil has two windings: It has one ground soldered in the upper left of the top photo. One wire is soldered to the red lead, and the white (center) lead has TWO wires soldered to it. They run together without any insulation between them and are joined to a larger terminal end that is soldered to the white wire. "


____ Okay, I've had to deal with this style of stator set-up before but I guess I had forgotten about exactly how it's actually wired-up. - (I've seen too many other wiring set-ups done on Italian made stators, to keep them all straight.)
With this 28-watt stator, the lighting-coil is center-tapped to share a little juice for charging the battery. _ I believe that most were wire-up this way. _ (I'm now thinking that the reason for why I was sure that the WHITE-winding [used to charge the battery] was together on the same power-coil with the YELLOW-winding [used to run the ignition], is cuz the similar 40-watt alt.model also uses a white wire-lead connected to it's power-coil that's for running the ignition.)
__ This particular wiring-method that was used for this stator of yours, allows modifications in a number of different ways! _ So before I make any suggestions, I'd like to know how comfortable you are with screwing-around with the various soldering-connections? _ As you could choose to do some elaborate modifications and end-up with a relatively complex system (as I've always chosen to do for myself).
Sticking with the simplest ("4 wire") modification, will only require for that 'ground' of that one coil-lead (from the darker power-coil), to be un-soldered & connected to a 4th wire-lead.
__ Please let me know what you're now thinking.


_Bob