MEP 002A "Slightly Over Voltage" Everything Else OK

[cuad4u]

As those of you who assist on this forum know, I bought 4 MEP generators in October 2013. With your generous assistance I got 3 of them running (2 each 002A and 1 each 003A). I used the 4th one as a parts donor to get the other 3 going. Lacking something constructive to do over January I decided to see if I could resserect the parts donor. A rebuilt IP, new relay A1, a new fuel hose, two new glow plugs, a couple of new gauges, and lots of cleaning and the donor MEP 002A came to life. I did the usual load testing and it worked perfectly for a month.

I loaned it out to a friend during the recent ice storm. I personally helped him wire it to his house via #6 wire to a 30 amp clothes dryer receptacle. I made sure he understood that he needed to do some "load management" and not try to run everything at one time. He ran it around 70 hours until power was restored. When I got the 002A back the output voltage was a bit too high. Even with the voltage adjust pot set at minimum (fully CCW) voltage was 260VAC and 130VAC respectively. Turning the voltage adjust pot clockwise toward maximum increased voltage to 310VAC and over 150VAC respectively. These voltages were verified by using the panel gauge and a Fluke 87 digital VOM. Hz is 60 and holds steady and varies with engine speed like it should.

I did the usual simple things like removing the cannon plug connectors, spraying them with DeOxit, and reinserting them. I disconnected all wires from the voltage adjust pot and it reads OK from minimum to maximum resistance. I have the TM and I did the "search" thing on this site, but I cannot find any specific reference to this problem.

Since the voltage adjust pot will adjust the output over a 50VAC range (260 - 310 VAC) does that mean the voltage regulator board is probably OK? How about the $3 voltage regulator board output transistor?

I am thinking either one or more of the small diodes inside the voltage / phase box or possibly one or more of the 4 diodes on the rear of the generator itself. Before I take the shotgun approach, I wonder if any of you "experts" could aim me in the right direction.

Thanks..............

 

[Isaac-1]

Did you try the adjustment pot on the circuit board?

 

[dependable]

I was going to write; Check trouble shooting (pg 2-11) and regulator test and adjustment (pg 6-8 )both in TM 5-6115-584-34. Isaac, do you mean one of the variable resistors on the VR board? I never did have to adjust one, is it R-17, the TM says R-15, not sure myself.

 

[cuad4u]

Thanks for the two replies. No I did not adjust a pot (or anything else) on the VR circuit board itself, because the 002A ran and produced the correct voltage (120V / 240V) and power for a month. Also when I got it running the panel voltage adjust pot would vary the output voltage from around 200V to around 260V or an adjustment of around 60V from fully CCW to fully CW. I think that is the normal adjustment range because the panel mounted voltage adjust pots on my other two 002A generators do exactly that.

Then "something" happened or "changed" while it was loaned out. When I got it back the panel mounted voltage adjust pot looked to be in the same apparent position (11 o'clock) as it was before I loaned it out. In other words the person I loaned it to did not "mess" with any controls or adjustments.

I assume my friend must have run it at least for a while on 135V / 270V because I do not know when the problem arose during the 70 hours it ran during the power outage. He did not burn out any light bulbs or other "stuff". Another thing is when I connect my 4500 watt 240V electric resistance heater that I use to load test, the voltage stays at whatever voltage is selected by the panel mounted voltage adjust pot. In other words the voltage regulator board SEEMS to be working, but I cannot bring the voltage down to anything less than 130V / 260V.

When I get home tonight, I will check the sections in the TM that were recommended.

 

[Ray70]

I think the resistor on the VR board that Isaac-1 and Dependable are talking about is R15 / R16 depending on which version of the VR board you have. Try adjusting it and see if it changes the min and max voltage achieved by turning the panel mounted voltage adjustment. Although this won't explain what happened to the machine to cause the voltage to change....

 

[cuad4u]

UPDATE - Got home and before getting out the TM I opened up the side cover on the voltage / phase selector box and the metering box where the VR is located to take a look. I was looking for something obvious like a loose wire or a burned component. Everything looked OK.

Just for the heck of it I decided to use a screw driver and make sure all screws that connect wires to terminal boards, transformers, switches, and other components were tight. They were. . None of the approximately 100 electrical screws were loose. While doing this I loosened each screw (about 100 in all - but I did not count) about half a turn and retightned each screw.

When I started the 002A up voltage was back to 240 with the panel mounted voltage adjustment pot at the 11 o'clock position just like before the problem started. I can use the panel mounted voltage adjust pot to adjust the voltage from around 200 in the fully CCW position to around 265 in the fully CW position.

I have no idea what I did to correct the over voltage condition unless one of the screws maybe had some oxidation between it and the connected wire(s) which caused a high resistance which caused the high voltage problem.

Once again, all seems well again. Over the next week or so I will run the generator under load and without load and see if the over voltage problem comes back or not.

I will let you know what happens. As in all trouble shooting I guess I need to remember to try the simple things first before suspecting a major component failure or worse.

Thanks again for all the suggestions.

 

[zoltarp]

Now I have to go home and do all mine too!

 

[steelypip]

I have no idea what I did to correct the over voltage condition unless one of the screws maybe had some oxidation between it and the connected wire(s) which caused a high resistance which caused the high voltage problem.

FWIW, I have experienced this problem on my 002 as well. It's not exactly a surprising problem with screw terminals exposed to temperature and humidity extremes. I would recommend that anybody try going over all the screw terminals first before doing more elaborate diagnostics for a flaky problem like this, versus a no-op problem.