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We are tinkering with DewCatTea Bobs diagrams https://youtu.be/BWXitFxhGQk installed a 25 amp 200 volt rectifier individually testing all three circuits of a 68 Ducati Scrambler 250 to see what would happen. We swapped the lighting circuit and the ignition circuit just for grins. Then we settled for making the ignition circuit the lighting circuit.

Is this colored markup of the magneto alternator correct for the 28 watt 6 volt Ducati Scrambler 250?

Here is a post and picture from the “at wits end post” viewtopic.php?t=2091

Would it be safe to assume that the above colored diagram would match his results as follows?

His white should be yellow
His red should be white
His green should be red


These were his resistance results
Alt wiring resistance measurements
White = 1.0 (currently connected to ignition)
Red = 0.4
Green = 0.1-0.3

Well, I don't understand what is in doubt here. Any easy way to find out whether the colors are right or wrong is:

Yellow and white (in Zoomersmoto's diagram) can't have any measureable connection to ground, the corresponding coil is electrically floating. Both wires are interchangable with respect to their connection in the loom. If any of these shows up a connection or resistance to ground (i.e. stator plate), this coil has an insulation fault, is damaged and shut be discarded.
Red: the correspondend coil has one end ground-connected, which can be easily prooven by a measurement with an ohm-meter or continuity tester.

cheers Hans

[quote="ducwiz"]Well, I don't understand what is in doubt here. Any easy way to find out whether the colors are right or wrong is:

Yellow and white (in Zoomersmoto's diagram) can't have any measureable connection to ground, the corresponding coil is electrically floating. Both wires are interchangable with respect to their connection in the loom. If any of these shows up a connection or resistance to ground (i.e. stator plate), this coil has an insulation fault, is damaged and shut be discarded.
Red: the correspondend coil has one end ground-connected, which can be easily prooven by a measurement with an ohm-meter or continuity tester.



Thanks Hans I was hoping you would answer.

Will double check continuity on the “floating coil”

However I am wondering if this diagram is even correct for our model. They didn’t list the diagram in the work shop book but had a footnote that said it was “similar” We get the correct ohm reading for each wire when grounded to the case.

Our wires are different but give the following readings:
If you ground the ohm meter to the case

White wire has 1 ohm
Green wire has .5 ohm
Black wire has .2 ohm

at idle doing the same procedure to ck vac we get:

White wire 21vac
Green wire 8 vac
Black wire 4 vac

Our bike easily start on both the white wire and green.


Did you watch our video on the bridge rectifier? The only wire generating enough VAC to convert to 12v DC is our white wire.

Just viewed your video. Could not understand everything, because I learned british english in school, so aren't familiar with your "Texas dialect". But I suppose I caught the main points.
A bridge rectifier imho makes only sense, if the coil connected to it's AC terminal is of the floating/ungrounded type. A coil grounded on one side (ore somewhere in between) needs no bridge but a single or dual diode.
Your resistance measurement clearly prooves, that all coil ends connected with the coloured output wires have a connection to stator/ground at their othe end. Your "hand coloured" schematics depict one coil as "floating", no ground connection, in agreement with the ws manual. Result: your stator is different from that shown in the manual, or the lighting/charging coil is defective, has an unwanted internal short to ground on one or more internal wire turns.
I suggest to find out what you really have in your engine. Forget all colours and their theoretical assignment to the coils. Take the stator out, and and follow each end of the copper wire on each coil. Look for the routing and the solder points, where the connections to the coloured wires are made. If your stator is either the 40W or 28W type, one coil (ignition) must be grounded by soldering that wire end on a lug, clamped under one of the mounting screws. Both ends of the other coil should solely end on soldering points. If this is definitely the case, the coil in question has actually a fault.
If I should help with the identification of your stator furthermore, some in-depth fotos of your stator would be very helpful.

cheers Hans

ducwiz wrote:Just viewed your video. Could not understand everything, because I learned british english in school, so aren't familiar with your "Texas dialect". But I suppose I caught the main points.
A bridge rectifier imho makes only sense, if the coil connected to it's AC terminal is of the floating/ungrounded type. A coil grounded on one side (ore somewhere in between) needs no bridge but a single or dual diode.
Your resistance measurement clearly prooves, that all coil ends connected with the coloured output wires have a connection to stator/ground at their othe end. Your "hand coloured" schematics depict one coil as "floating", no ground connection, in agreement with the ws manual. Result: your stator is different from that shown in the manual, or the lighting/charging coil is defective, has an unwanted internal short to ground on one or more internal wire turns.
I suggest to find out what you really have in your engine. Forget all colours and their theoretical assignment to the coils. Take the stator out, and and follow each end of the copper wire on each coil. Look for the routing and the solder points, where the connections to the coloured wires are made. If your stator is either the 40W or 28W type, one coil (ignition) must be grounded by soldering that wire end on a lug, clamped under one of the mounting screws. Both ends of the other coil should solely end on soldering points. If this is definitely the case, the coil in question has actually a fault.
If I should help with the identification of your stator furthermore, some in-depth fotos of your stator would be very helpful.

cheers Hans

Hans, as Texans we are curious as a hound dog staring at a squirrel even when we are barking up the wrong tree. I hope you don’t think we carry our brains in our back pocket! Your advice make me happier than two tassels on a titty dancer! We do like to figure things out without our women having to take their boots or spurs off! But in this case it looks like we will have a peek in her britches! Will get you some sexy pictures.

ducwiz wrote:Your resistance measurement clearly prooves, that all coil ends connected with the coloured output wires have a connection to stator/ground at their othe end.

cheers Hans

One more thang...I really enjoyed the bantering between you and DewCATTea Bob. I am curious as a cat with 9 lives and was wondering how Bob came up with the same resistance measurements as we did if the mag alternator is defective? Can I just check the resistantance between the individual wires like a normal 3 phase stator and two should have a resistence with each other like you and Bob did?

It took me a dictionary, a translating machine on the web and a joyful while to translate all your idioms
Seems the Hessians, where I live in southern district (Hesse is a state in the heart of Germany https://en.wikipedia.org/wiki/Hesse), are as curious as the Texans. Hence, I continued researching about Ducati singles alternators, and finally found this:



Here we see the sketch of a stator with the usual 3 output wires, but 2 internal ground connections of windings. It must contain a special winding scheme, as well as at least one coil in dual-layer fashion. OK, it should belong to n/c models, but your early SCR might have this type anyhow, so measuring 3 certain resistances against the stator is a matter of course in that case. I feel unable to answer your question about resistance values measured as long as we have not perfectly identified the type of stator in your bike. Let's unravel that mytery!

Don't be afraid of beeing misjudged - seems your brain sits in the right place And btw, some important info about Hessians, maybe unknown in the US: https://en.wikipedia.org/wiki/Hessian_cuisine

Hans

Zoomersmoto wrote:Is this colored markup of the magneto alternator correct for the 28 watt 6 volt Ducati Scrambler 250?

After scrutinizing the n/c workshop manual and other sources (see above) I conclude:

You posted the correct schematics for your bike (engine no. after 92171),


but the wrong picture for the alternator internals:


It belongs to the schematics for the early SCR (engine no. till 92171), ought to be associated with it:


Until eng. # 92171, a pure AC system was implemented, no battery, no stop light, separated AC ign. circuit. The wire colours might have been black, blue an unknown; those in the "at wits end .." post are different. the wires look quite new, like having been replaced.
Unfortunately, we do not have a sketch of the stator's inner circuitry. It's clear that your stator has no floating coil for lighting power, but indeed an inner ground connection, and two power outlets. We still do not know whether this "dual coil" is grounded on one end of the windings, or somewhere in between. This can possibly be found out by measuring the resistances and by tracking the output cables down to their solder spots/coil ends.
You found in the post mentioned above:

White wire has 1 ohm
Green wire has .5 ohm
Black wire has .2 ohm

Then you quote:

His white should be yellow
His red should be white
His green should be red

Your wire colouring:

Our wires are different but give the following readings:
If you ground the ohm meter to the case

White wire has 1 ohm
Green wire has .5 ohm
Black wire has .2 ohm

Well, I can't see any difference in colours when comparing yours and those in the other post
I understand that you scibbled the colours as depicted in the (correct) schematics of your loom onto the wrong stator schematics.

Now again: as long as we have no reference stator from somebody's stock, or your own at least visible in mounted position, we will not make any step further.

cheers and good luck Hans