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XT550, faulty rectifier/regulator – will the stator be destroyed if disconnected?

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My '83 XT550’s rectifier/regulator is faulty. I don’t know in what way, but there is no voltage over the battery.

If the rectifier/regulator failure results in too low resistance the stator probably will burn (too much current).

If I disconnect the rectifier/regulator the voltage will go up, but how high? Is it possible that the voltage will go high enough to destroy the isolation?

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no you have it wrong. the stator and lighting coil only have the potintial to make power. They will not make power without something connected to DRAW the said power. An altinator is not like a power source you have to hold back. It is more like a gas tank that you stick a sifon hose in. But an altinator only makes enough power to supply what is being drawn from it, even though it has the potintial to make a lot more than is being drawn Thats about the best i can explain it. Just dont forget grounding/shorting can put a high current draw on a system that could fry something. But just disconnecting all the draw from the lighting coil will not hurt it, it will accually stop creating power until it has a draw on it again.

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Thanks yellowsnow.

You are right of course. Big current can fry the stator, that is why I want to disconnect the regulator/rectifier, the unit is faulty and I don’t know what it will do. If the resistance of the unit (rectifier/regulator) is too low the current from the stator can get too large. I don’t know how much the risk is, since I don’t know the thickness or “gauge” of the stator coil wire and I don’t know the “inner resistance” of the stator coils. The problem is that I have no specs.

What worries me is what happens when I run the bike with the stator circuit open, some generators have the potential to build high voltage when no current is drawn. I don’t expect the voltage from the XT’s generator to build that high but I am not 100% sure, I just don’t know. If the voltage builds excessively the insulation between the wires in the stator coils can break down.

I would expect it to be perfectly safe (to disconnect the stator from the regulator/rectifier) but since I have no specs I am 98% sure and not 100%. So I am hoping that someone will YELL at me if I am about to do something stupid… :-)

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"some generator can make high power with no draw on them" that would be an interesting phenominon.the question is, if this phenominon des happen, does it still put a drag on the rotating assembly? maybe you are thinking of voltage spikes during a DC gen start up, like what Tesla was so interested in. i get into the whole free energy thing. i think your safe discnnecting the cuircut though.

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Thanks yellowsnow. I am thinking of high voltage (volts) but no power. When there is no current (ampers) there is no power (watts). But the voltage can get high.

I hooked up my multymeter to the stator and ran the engine for a short while in the garage. The highest voltage I saw was 75 volts (AC). Of course I did not run it at max RPM’s in neutral so the voltage will climb a little higher at max RPM. My guess is a little over 100 volts AC. That’s not that high..

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Is your battery any good? I thought I had a rectifier/regulator problem and it turned out to be the battery instead.

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Smacaroni, you are spot on. Yesterday I did some more measurements, got the usual silly readings, and decided to try again with the battery from my KTM EXC400. Bang---14.5 volts DC. So a good battery is vital, just as you said.

Yesterday night I went for a short ride for the first time. The DIY CDI is only firing on the 12° pickup (before TDC) but still the bike is not that bad, I expected worse. The ride took me back, I had a XT550 years ago and loved it...

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Yeah, the pulser coil on mine took a dump too, limited to 12 degrees. It's find till 3,500 RPM on the stock CDI, after that it tends to puke all over itself unless you free rev it.

A friend and I are working on a replacement CDI. The 12 degree only CDI runs very similar to the stock unit, I had it out on the highway at an indicated 80 mph! Which is probably good I didn't go any faster, the tires are only rated to 81.

If I can get my hands on a second pulser coil, I'll do a DIY 12/36 degree pulser, but I want to have two on hand for disassembly (the gifted one and my own) since I expect some sort of surprise when I cut it open. I highly doubt it's going to be a straight forward remove these two screws and open a cover kind of deal. I think it will be like an archeological excavation to get that thing apart. Once I have it in pieces though, I think it's going to be simple to make a replacement.

*crosses fingers*

I totally agree they're great bikes. The only thing I would change if I could is a disk front brake. I love riding that thing in parking lots too, "speed bump" is not a threat, it's a challenge!

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If the 36 degree side of the pulser has crapped out, the CDI isn't the problem. The problem is Yamaha decided that the pulser is part of the stator and to replace one, you have to replace both at a cost of $550 or so. It's nearly impossible to get a used pulser coil and while I think building one is entirely possible for the shade tree mechanic, no one wants to give up their half dead pulser coil so I can do a write up on it.

I'm willing to sacrifice mine, but I really want a second one on hand in case disassembly is a disaster.

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