TOPIC:

If you put the stock one back in and have the same readings, that will narrow it down to the stator or rotor.
Steve

Nessism wrote:
"To do this with a meter: black lead to battery ground (does this mean I connect the R/R - output terminal to the battery - post?), red lead to each pin on the plug (what does "red lead to each pin on the plug mean? What pins? The pins for the stator input?), start with the voltage scale higher than 12vdc and move voltage scale down in steps for each pin. Any voltage is a bad regulator."

It's not a bench test. This is on an installed R/R. Unplug from the stator connector, put negative lead on battery or frame ground and touch each of the 3 leads in turn and see if you get any voltage readings.

Okay, did the test and found that there IS voltage at the stator connection terminals. I was thinking some diodes in the system would have prevented this but that's not the case.

Nessism wrote: Okay, did the test and found that there IS voltage at the stator connection terminals. I was thinking some diodes in the system would have prevented this but that's not the case.

yeah I figured it was an easy diode test. Did you do the test in the vid I posted?

GPzMOD750 wrote:

Nessism wrote: Okay, did the test and found that there IS voltage at the stator connection terminals. I was thinking some diodes in the system would have prevented this but that's not the case.

yeah I figured it was an easy diode test. Did you do the test in the vid I posted?

I don't see any video so the answer is no.

Edit: found a video earlier in the thread. Sorry, I didn't test the R/R any further than just doing the test like you directed.

That test, using a meter, is not a very good one. Any diode or transistor will have some minuscule amount of reverse leakage. If a voltmeter, especially a digital voltmeter, has a really high input resistance, which is what is desired in a meter, the meter will measure that reverse leakage as a significant voltage (in that particular test, because there is a voltage applied), even though there is almost no current flow.

There is a misconception that when a transistor is turned off, or a diode is reverse biased, that they act like an open switch. They don't. They just act like a very, very high resistance, instead of an open circuit. Exactly how high will depend on the device being tested, and even worse, will depend on the internal workings of the meter itself. That is why resistance tests on semiconductor devices are always sketchy.

The test-light version of that test is better because it will require a pretty significant amount of leakage to light up the light bulb. That amount of leakage is a good indicator that a diode is bad, or even completely shorted. Test-lights differ from a meter in that they don't have a super-high input resistance.

BTW, it's not really testing the regulator portion, but actually testing the rectifier portion of the reg/rec. A series-pass regulator might not have a full diode-rectifier because it is switching on transistors to allow current flow. So I'm not sure the same test results would be valid for both types of reg/rec (the stock type is shunt, the newer type you ordered is series-pass).

This thread reads like an instant replay of what I went through on my 750E. Low charging voltage. I tried two different stators, several different R/R's (including one from my other bike (with soldered connections) that was charging well. I checked no load AC voltage on the stators, resistance on the stators, etc. Everything tested out well, but still low charging voltage. Several hours of my life wasted and a LOT of frustration. I just couldn't believe that both stators that looked bright and clean, no dark burned spots anywhere, could both be bad. In the end I ordered a new stator and the problem was solved.

I'm NOT saying this is the case for sure here, just that it's smelling that way. Buy a new stator and worst case, sell it to someone else if it turns out the problem is something else. That's what I concluded on my bike anyway.

Those same symptoms could happen if the magnets are weak. So it could be a stator, but could also be a rotor. A stronger, aftermarket stator could resolve the issue in both cases. (Which would explain why replacing stock stator with stock stator was not the fix.)

There have been so few cases of 3-phase, permanent-magnet, 650/750 charging issues over the last 15 years on Kzrider, it's hard to estimate what is more likely... stator or rotor. Magnets do lose intensity over time, but stators degrade too.

Even with all of the 1-phase 650 charging issues, the solution was usually to replace the stator with a 3-phase stator, or aftermarket stator. So even in those cases, it was not known for sure if it was stator or rotor.

But as Ed says, the solution may be the same either way... new aftermarket stator. Unless you can get a "known for sure" good rotor for dirt cheap. Does anyone even sell new 750 rotors? Probably not cheap.

GPzMOD750 wrote: I swapped the first stator back In and ran the tests. I'm getting 66 +/-VAC @ 4000 rpm and 78 + VAC @ 5000 rpm. I hooked up the R/R and I'm getting Approx 13.5v-13.8v from 2k-5k rpm. It stops charging at approx. 1000 rpm.

This is what I don't understand. Those results are exceptionally good. 66v AC @ 4000 is way above the FSM's expected 50 v AC, and way higher than what I get on my 550's which charge fine (the FSM spec is the same for the 550).

So the second stator was around 55 v AC at 5000 rpm, and the first one is 78 v AC at 5000 rpm. Correct?

Stators break down over time with internal leakage between the windings/ground. Run an insulation resistance or dielectric test on a 35 year old stator and it's sure to fail.

In my more than 10 years of restoring old bikes and hanging out on motorcycle forums such as this one and the GS Resources, I've yet to hear of one confirmed case where failing rotor magnets had an effect on the charging system power.

Oh, and a bike that charges at 13.8 volts will get down the road pretty well if the battery is strong. I helped a local guy work on his GS750 and after installing a new R/R he was only getting something like 13.5 volts. I told him his charging system is on borrowed time and to start saving his pennies for a new stator. That was two years ago now and I haven't heard back from him since.

loudhvx wrote:
So the second stator was around 55 v AC at 5000 rpm, and the first one is 78 v AC at 5000 rpm. Correct?

Correct.

I rode to work this morning and I checked the voltage 4 or 5 times and was getting just under 14v at 5-6k. If I can get the same results consistently I'll be happy.

This is with a freshly charged batt. The same would happen with the old R/R, charging would drop slowly for the next few days as the batt lost charge.

My resistance between stator leads is 1.5 ohms which is double what it should be. I'm weighing options on stators....

This is why I hate electrical. It all seems to be theory with no definitive parameters. It seems the only thing constant is to screw around with it until it works or you release the magic smoke. Then you're SOL.

It's pretty common for people to want to remagnetize old rotors, especially on English bikes. Since new rotors are not often an option, people change the stators.

I prefer working on electrical because it is measurable with cheap meters and scopes, but it's not intuitive, and is difficult to troubleshoot remotely for sure.

When I test alternators, I use an active load tester I designed specifically for this purpose. That way there is no question.