Overvoltage MEP002

[Harleyd315]

I have a 002 that runs great but has a high voltage condition. Starting the unit the voltage goes up to 140/260. I tried adjusting with the rheostat but even turned all the way down it still stays high. I have checked with my other test meters and the voltage reading on the set are correct 140/260 output. A couple of times I was able to stop the gen and restart it and had good voltage readings. I looked in the TM and did try to adjust R16 but it made no difference. This unit appears to have been totally rebuilt and all the components/gauges in the control box appear new including the volt regulator. Can the rheostat be the problem? And if so how to test. Or am I looking more towards the AC voltage regulator. Any help would be appreciated, Thanks

 

[ClarkeF]

The rheostat could be the problem if it's shorted. A simple resistance check across the outputs of the voltage adjustment resistor R1 should tell you if it's working or not. You may need to disconnect a leg, but from the schematic only one.

 

[coyote62ny]

first thing have you ever idled the engineor run at less than 60 hertz? if you have done this you may have fried the ac voltage regulator point is never idle these gen sets set the throttle to 60 hertz and then forget it has a throttle clarkf has told you how to test the reostat as well as the resistor it should tell in the tm about testing the reostat you may have to remove the connections wires attached to the reostat to test it it should adjust from a low point to high point without any sudden jumps should be a gradual transition from low to high hope this helps you out keep us posted on your progress

 

[RJM27]

first thing have you ever idled the engineor run at less than 60 hertz? if you have done this you may have fried the ac voltage regulator point is never idle these gen sets set the throttle to 60 hertz and then forget it has a throttle clarkf has told you how to test the reostat as well as the resistor it should tell in the tm about testing the reostat you may have to remove the connections wires attached to the reostat to test it it should adjust from a low point to high point without any sudden jumps should be a gradual transition from low to high hope this helps you out keep us posted on your progress

My inital thought was, have you checked the Hz, with your own meter the Gen-set meter.

 

[RJM27]

My inital thought was, have you checked the Hz, with your own meter (NOT JUST) the Gen-set meter.

 

[Harleyd315]

Thanks for the advice. I'm not sure if anyone ever let this set run at less than sixty hertz, I just got it running and the over voltage condition was present. This set was reset before I got it and has a rebuild tag from an outside vendor on the fan cover. This is the first set I ever had that the throttle cable does not go to idle, with the throttle cable all the way in it still is at 1800 RPM 60 Hz. Someone must have set it up to be fool proof?? Any way all my sets are set to 60 Hz and thats how I leave them upon shut down, breaks my heart on them cold mornings but I know what can happen if you let them idle. I have a fluke meter so yes Voltage and HZ were checked. Rheostat was checked and is functioning. I took a good voltage reg out of another set and that seemed to correct the problem. Now to find some one who can repair that. Thanks again for the help.

 

[coyote62ny]

there is a transistor that goes bad causing this problem you can replace the transistor your self it is held on vr board with 2 screws the replacement transistor most people thatwere replacing them were using was a 2n5631 this is what normally goes bad i got this info on this site i have looked at my 003 and it is easy to replacehope this helps you get it going you could also try delks for a vr but it will be pricey or tom at gulf coast trucksoffice 1-281-422-3200 cell 1-832-323-1445 tom would have a good used one he tests his used parts and reasonable prices delks number is1-336-629-0991

 

[Harleyd315]

I sent mine off to Tom at Gulf Coast, he said he would fix mine and test it. Very reasonably priced and a great guy to help you out.

 

[coyote62ny]

glad you found someone to repair your vr yes tom is very helpful and reasonable with his prices

 

[RichardR]

Harleyd315,

I agree with coyote62ny. Your high voltage problem is due to a failed voltage regulator board. The usual symptom of failure of the VR board is high voltage (you might expect it to be low voltage, but it's not). Tom at Gulf Coast will get you going again, but you could probably fix it yourself if you are electronically inclined. I think the VR board and its components are well documented in the TMs.

Richard

 

[Harleyd315]

I can usually diagnose 12/24 volt electrical problems without to much trouble on most equipment I work on. But the schematic's on these keep me scratching my head and I get lost.

 

[RichardR]

Harley,

A one-paragraph explanation of how the voltage regulator works can be found in Section 6-3 of TM 5-6115-584-34. Nobody I know has been able to translate that paragraph (or any of the rest of the TM) into useful information for diagnosing VR failures and knowing which part of the VR may have failed or what caused it to fail.

What I have heard from folks who know better than me is that the VR system on the -002 and -003 is similar in operating principle to the Magniciter regulator that Onan used until about 1972. A key part of the VR system is the linear reactor that resides in the AC Output Control Box, not where you might expect to find it next to the VR board in the meter Control Cubicle. There is a complete description of how an Onan Magniciter works over on the SmokStak board.

My understanding is that Onan quit using Magniciter regulation mostly for cost reasons. It is a very reliable and rugged system, but more modern technology is just as good, and cheaper. None of these reasons would affect DOD design decisions, so we have what we have in the -002 and -003.

Fortunately for us, we have the history of many years of maintenance and repairs of -002 and -003 voltage regulators, so folks who know this history can quickly zero in on a problem. My bet is that coyote62ny is right with his failure diagnosis, but you would have a very hard time figuring it out by looking at the schematics and the description in the TM. Tom at Gulf Coast will have you up and running in no time.

Regards,
Richard