MEP-802A intermittently overvoltage faulting stall

My MEP-802A recently will stall at startup from an overvoltage fault. The voltage adjust potentiometer can raise the voltage and make it stall so that seems to be functional. Any ideas? Could this be a bad voltage regulator causing higher voltages? Bad voltage adjust potentiometer? If I start and stall the machine several times, it will get back into range and work. This problem just started. Before this, it ran an hour each month without problem for the last two years.

Have you seen it happen or does it happen when you aren't looking?

When you move the voltage adjustment knob on the panel does the voltage change smoothly or is it jumpy?

I would check all the wiring connections and exercise the adjustment pots some. Pull the top cover over the control panel and look for any signs of mouse damage.

DieselAddict said:

Have you seen it happen or does it happen when you aren't looking?

When you move the voltage adjustment knob on the panel does the voltage change smoothly or is it jumpy?

I would check all the wiring connections and exercise the adjustment pots some. Pull the top cover over the control panel and look for any signs of mouse damage.

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It generally happens within a few seconds of starting, though just today it stalled out for the overvoltage after 15 minutes of running fine. That was the first time it happened, which leads me to believe the problem is progressing. Moisture/corrosion somewhere? The voltage adjustment is smooth.

Thanks for the rodent suggestions. I had the generator loaded with d-con for mice but I did see a couple acorns from a squirrel near one of the batteries.

Do you have the QUAD circuit mod? Or the MOV mod on your set?

Guyfang said:

Do you have the QUAD circuit mod? Or the MOV mod on your set?

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No, I don't have any mods. Should I?

If your volt reg is bad, in the over volt way, you can possibly do very bad damage to your main generator. So what you should do is look search in the forum for the info about these mods. I would normally point you in the right direction, but have to go to a concert. So start looking, or send a PM to Daybreak.

Guyfang said:

Do you have the QUAD circuit mod? Or the MOV mod on your set?

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I have the QUAD winding fuse mod on my unit. That must have been done by Uncle Sam before I purchased it. I just ordered an MOV. Hopefully it will arrive before the next power outage and there isn't already damage to my voltage regulator.

On a related note, I exercised the voltage potentiometer serveral times and haven't been able to reproduce the over voltage fault again today. Maybe is was as simple as a corrosion?

It might have been just the R1, but I tend to think problems don't just "go away". You need to exercise the set a few more times to make sure. Even then, be wary. Let it set a few days and try again.

The problem still exists. I am going to try the MOV install when it arrives, but it looks like the next step is either repair or replace the VR. It looks like original VR replacements run about $275 and aftermarkets run about $150. Anyone have experience with VR repair or replacements?

DieselAddict said:

I would check all the wiring connections and exercise the adjustment pots some. Pull the top cover over the control panel and look for any signs of mouse damage.

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Did you follow DieselAddict's suggestion to pull the top cover and look for mouse damage? I'm thinking a shorted wire somewhere in the unit. Many folks on SS have found worn insulation and shorts from wires touching the sides of the generator.....and my 802 vibrates quite a bit. The intermittent nature of your fault makes me think electrical short.

As far as I know, no one rebuilds them. I wish for you guys, someone did. Then maybe the thing could be done right.

Update: I installed the MOV and the last dozen starts have been good without stalling from the OV fault. However, the weather is slightly warmer so that may confound the results. As a backup, I purchased a new VR and plan to learn the ancient art of VR refurbishing if indeed my VR is bad.

If anyone needs an MOV, I had to buy a multipack. I would be happy to sell them off at cost to whoever needs them if you PM me.

Let me put a set of eyes on my personal 802 soon (or my soon-to-be-personal 802)... might need to take you up on one. Thanks

The problem reared its ugly head again just when I thought I was in the clear. From my research, I suspect a diode may have gone bad from not having the MOV mod protection. Since I replaced the original VR with a brand new one, I am now in the middle of pulling out each component on the original VR circuit board one by one and testing / replacing each one starting with the diodes in the red box of the attached image. It would be great to find a "smoking gun" bad component in this process which would then give me a backup VR and hopefully help anyone else that has a similar problem. If anyone happens to have a bill of material of these PCB board parts, that would save me a little time!

If you replace the diodes it's recommended that they get replaced with 1N5408's.
They have a higher PRV rating than the stock ones.

There is also a thread where someone replaced the stock A1 with a SX460.
https://www.steelsoldiers.com/showthread.php?177057-Alternative-AVR-for-MEP-803a&highlight=SX460

I found some related generator overvoltage information on another site that seems relevant to my problem.

1) Over voltage on a generator is typically caused by one or a combination of the following:



-Faulty Voltage Regulator and needs to be replaced

-Frequency (hertz) of the generator is not properly set. Too high of RPM's will cause an over voltage

-Located on the Voltage Regulator, there should be a Voltage Adjustment Potentiometer. This is an adjustable electronic component that can vary the voltage output.

-Stator problems either on the stator power windings or the stator excitation windings.


2) Recommend to check the voltage potentiometer 1st and adjust if needed. If that does not resolve the problem, next would be to check the frequency output and high RPM's. If still a problem, recommend checking all sensing and control wire connections from the stator windings back to the voltage regulator. Next would be to replace the voltage regulator. Last would be the stator windings are shot and need to be re-wound.



3) Most common problem will either be a faulty voltage regulator or too high of RPM's

In addition to the VR, I am going to pull the top off and go through the wires from the stator to the VR to make sure there isn't connection damage as others have suggested. The VR may just be a symptom of the problem.

gen508 said:

I found some related generator overvoltage information on another site that seems relevant to my problem.

1) Over voltage on a generator is typically caused by one or a combination of the following:



-Faulty Voltage Regulator and needs to be replaced

-Frequency (hertz) of the generator is not properly set. Too high of RPM's will cause an over voltage

-Located on the Voltage Regulator, there should be a Voltage Adjustment Potentiometer. This is an adjustable electronic component that can vary the voltage output.

-Stator problems either on the stator power windings or the stator excitation windings.


2) Recommend to check the voltage potentiometer 1st and adjust if needed. If that does not resolve the problem, next would be to check the frequency output and high RPM's. If still a problem, recommend checking all sensing and control wire connections from the stator windings back to the voltage regulator. Next would be to replace the voltage regulator. Last would be the stator windings are shot and need to be re-wound.



3) Most common problem will either be a faulty voltage regulator or too high of RPM's

In addition to the VR, I am going to pull the top off and go through the wires from the stator to the VR to make sure there isn't connection damage as others have suggested. The VR may just be a symptom of the problem.

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I just don't see that. I have never seen a gen set VR go bad for too high RPM. RPM and voltage have nothing in common. RPM=engine speed. Too little RPM can cause a problem, but too high? Don't think so.

Have you ever seen the voltage too high? If not, then you could just as much have a bad K8, as anything else. Take a step back, and re-look. Try starting it up, with a Volt meter hook up to the 120 volt outlet. WATCH the meter. Nothing else, see if it even moves, from 120 volts. Do not assume its the VR. Prove its the VR.

Triple Jim should chime in on this one. I've always been told that running the unit at idle would cause damage to the VR. But TripleJim states that running the unit excessively over in hertz would cause the VR to fail. This relates to the 002a and 003a but I would think it would relate to these units too.

Did you ever find the problem? My 803 with the quad mod will run for a couple minutes then voltage will spike and peg the meter and the unit will shut down. If run in battle short voltage stays constant and everything runs fine. I don’t like being in battleshort even though I have verified proper voltage so I’d like to find the root of the problem.