Tag Archives: electrical

Advanced stator surgery: Building a 6V VBB compatible P stator

So, I’ve run into a problem I’ve had to solve before. Figured I’d write it up.

Most non-battery 60’s and 70’s Vespa scooters use a system first used on the VBB2; it’s a quirky system where the load functions to limit the voltage. The whole system balances without a voltage regulator. Problem is, because of the way this system works, it’s completely baffling to most people, and you can’t just hook up a later engine from a P (or PK , for small frames)  easily. And a lot of people want to do that. You can hack into it and fiddle with the wires, add a few, change the brake switch, and you can come up with a system that sort of works, but really the best way is to rewire it from the ground up.

But, there’s an easier way. Piaggio did carry this style of 6V non battery electrical system forward into the P Stator designs. In fact, they even manufactured a few non battery, non turn signal, 6v P200’s in the late 70’s. But alas, that stator isn’t available any more. However, there is a stator much more plentiful and still available new that had this lighting system, in this stator design.

The ET3.

These use the same core setup as a P, but on a smaller diameter backplate. And the ET3’s were pretty much all non battery 6v. We can use the ET3 stator and transfer the coils over to a P stator to end up with a stator that is compatible with that old 6V bike we want to drop our P engine into.

So first: The stators.

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Late US P on the left, ET3 on the right.

As you can see, they are very similar in design. What we will do is remove the coils from the ET3 backplate, and transfer some, or all to the P backplate.

There are wires tying the coils to each other and the odd ground wire in the center. These connections need to be de-soldered. There are also the wires that go out to the junction box. These need to be either cut or run in such a way as to allow the coils to be removed. When doing surgery on stators this old or where they are going in a vastly different setup, I usually cut them and rewire the stator when I am done, making sure to leave enough length so I can identify the color of the wire that went there originally.

These coils slide onto the center core, and then have one of the laminations folded down to lock the coils in place. Like this:

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So, that in mind, let’s begin. We un-bend the laminations like so:

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It is also important to note that two of the coils overlap the other two, so it matters which ones you remove first.

These are the ones that need to be removed first:

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Now, to make this work, you are really only after the yellow/blue coils. These two power the tail, brake, and pilot lights. For the headlight, one can choose to use the P’s headlight coils, if the donor stator is an American market bike, or any two of the lighting coils if it is the European market style stator. If this is done, you end up with a hybrid; a 12V headlight yet a 6v brake/tail/pilot circuit. However, I didn’t trust the headlight coil on this P stator so this one is being built as a full 6v system, using all of the coils from the ET3.

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And here we have the core from our donor P stator. Then, we remove the coils from the ET3 stator. As I remove them, I like to place them on the table in such a manner that I do not get them installed incorrectly.

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And there is a problem.

See, there are actually two different types of P stators. This is the later one that has extra laminations so the lighting coils can be a larger diameter. You can see them on the picture above. The ET3 stator we have, being an original early one has the thinner coils. So these extra laminations need to be removed.

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On this one, I cut them in two places. The first shown here; then I cut on the other side of the next one, then ground down the rivet. After that, it was a matter of spinning them on the rivet and gently prying to get them loose.

Granted, not all P stator kitbashes will end up running into this early/late difference but if you run into that, you’ll know what you are looking at.

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And here is the stator with the extra laminations removed so the earlier coils will fit on it.

Incidentally, visually it is very apparent that these coils have very different characteristics, owing to the vastly different gauge and number of turns of wire on them.

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Here are the ET3 coils on the P backplate, before being re-wired.

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Here they are with new wires installed.

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I did have to get a little creative with the grounds, as i had to cut the original ground tabs off to get the extra laminations off.  I ended up grounding to the pickup mounting screw instead.

I just have to put the outer housing on them and cut to length and install connectors, and this stator can be installed onto any P engine and make it connect directly without adaptation to the vast majority of older non battery bikes. If done right, it should power a 12v 35w headlight and 6v pilot, brake and tail without any modifications to the harness, or adding any voltage regulator.

A little different than most people would do in this situation, but easier in some regards.

If one wants to undertake this modification, ET3 stators are available new in two types:

RMS brand and OEM Piaggio

Either will work, and as usual the Piaggio is more expensive.