MEP-005A high voltage problem.

I got my problem child MEP-005A running today (fuel pump problems) and everything was looking good for a while. With exception of the Hz gauge. Seems like that is an issue with all of the ones I have played with.

So I was running the genset to warm up the engine with no load and the main contactor open. Voltage looked good. Hz was set with an external Fluke meter. It ran fine for about 10 minutes. Then, all of a sudden, I heard the pitch of the generator change. RPM was constant and Fluke said 60 Hz. I looked at the panel gauges and noticed the voltage was at about 260v on all phases. I quickly turned the voltage control rheostat down all of the way and the voltage did drop. But the voltage was still too high. I shut the genset down and started checking wiring harness connections and all looked good.

I read through the TM troubleshooting and it said to repair the voltage regulator. Is this something that people have seen? Before I go digging in the VR, I thought I might ask if this was the proper course or if something else may be causing the issue. I'll go elbow deep in the VR if I have to though.

Steve

The little bit of overvoltage problems I had, always led to the volt regulator.

I have not taken the VR off to look at it yet. It may be simple to fix as it the voltage still can be "adjusted" with the knob on the control panel. It is just too high. But I was also wondering if the cheap SX460 AVR units could replace the original. I found a lot of posts where people with the smaller gensets did this. But only one thread where someone attempted this on a MEP004 but they did not report back success or failure.

Ahh... A bit of corrosion going on here. All of the glass packaged diodes took a hit. I wonder if some reaction was going on with the potting compound?

The diodes had QMJ 4246 markings on them. The best I could work out is that it is equivalent to a more modern 1N4246 in a DO-41 package. I didn't have any of those but it looked like a regular 1N4004 would suffice. 400v 1a. Of course, anything is going to work better than what was in there.

I had started removing the potting compound and a few of the diodes in these pics. The diodes mostly just fell apart. I have no idea how the voltage regulator ever kept the voltage good for the first few minutes of run time. I guess they were literally hanging on by a thread.



Cleaned up, both sides.


And the repair. All of the leads were bent over on the traces and soldered, so I duplicated. Been a while since I have seen that!


I'll throw this back on the genset tomorrow and see if it works before going any further. All of the other components looked good but I did not test any of them because of the potting compound. If it doesn't work, I will go a bit deeper.

The rest of the VR and static exciter looked really good. Nice transformers, no scorching, and pretty clean. Some of the nuts and screws that were not plated are a bit oxidized though.

Steve

Nice job. The N4004 diodes will be great. Pretty much any of the ones in that series would work well.

The $10,000 question: is it working OK now?

Heh... maybe not $10,000, but more like $350? I will have to wait another day. I thought I would get a chance to get out there today but I just got too busy with other stuff. To be honest, I think I was procrastinating because of the temperature...

Steve

Temperature? WTF!

It's about 3 below right now, and expected to be about -20 tonight. I had to work outdoors much of the morning--my fingers are just warming up now after about eight hours indoors.

Do keep everyone updated!

Success!!! So I guess it turned out to be a $5.00 question. Voltage is rock steady and can be adjusted via the control panel. The volt gauge is even spot on. Now I will do the single phase mod that sewerzuk was so nice to provide us. I have a 6PDT switch that will switch the CT resistors and control panel wires in and out so that switching to and from single phase to three phase is a simple matter of moving a jumper and flipping a switch.

Hz gauge is even coming back to life. It starts swinging back and forth a bit the more I ran the generator. It is an adjustable type so I may tweak the set points just a bit and see if that helps it out. I had another Hz. gauge come back to life, so maybe this one will too. The other one that came back just started working after about 2 hours of running. Dead on frequency too. It frustrates one a bit when things can just stop and start though. They will probably get the little digital frequency meter treatment just for redundancy.

In any event, I think this one is a keeper. 18 hrs. since the 2007 depot reset. New engine, etc...

Steve

Definitely 'tweak' the Hz gauge transducer's pots. Mark the current position well, then run them from zero to full a few times, and reset them to the points you marked. The connect the meter to the transducer, and the input to the transducer to any 120 volt outlet in your shop. If it doesn't read 60 Hz then touch up the adjustments until you get 60 and you should be good to go. Since you are not going to run on 50 Hz, the setup and calibration is easy. And the 60 Hz line frequency of your shop outlets is rock solid and accurate. I've had success doing just this myself.

And congrats on the fix of the voltage regulator!

Nice job getting it repaired.

The generator should have shut off when the voltage increased.
You may want to find out why that didn't happen.

I was lucky. My voltage increased during one of my once a month test runs before I connected it to the house.

Brian

Brian,

I was just reading your post about over voltage! I don't know why I didn't find it when I was searching the forum for OV problems. Did you end up replacing those diodes?

I will check the start/run switch for the wiring issue you found. Maybe the regulator is responsible for providing a OV feedback signal and the corroded diodes prevented the signal?

In my experience with 3 MEP005s, it is quite easy to test the over voltage shutdown once the sewerzuk single phase mod is done. Just start up at full throttle with the voltage knob turned fully clockwise. The engine will start and come up to speed and immediately shut down with OV. The start procedure I use now is pull half throttle and turn the voltage adjust fully counter clockwise, start the generator, and when voltage comes up adjust Hz then voltage.

I have not done the single phase mod on this one yet. That is a project for a warmer weekend. Once I do, I will resolve the OV protection problem.

Steve

My problem seemed to be caused by moisture which affected the diodes. I did replace the diodes and at the time most of the components on the board. I am still working on a problem were I can’t pull more than 20K watts from it without cycling problems.

http://www.steelsoldiers.com/showth...-Load-Bank-Test-w-problems&highlight=mep-005a
Anyway, I have since replaced every component in the exciter/voltage regulator assembly except for the transformers. I’m waiting for warmer weather to deal with that problem.

I haven’t tried forcing an over voltage that way. I start my engine at half throttle and leave the voltage adjust were it was. That seems to work for me.

Brian

This is the thread I was looking for

I am still having under voltage issues with mine. Flying dude did you get your generator working?

Mine is working fine as long as I stay under 20K. Still waiting for warmer weather.

Have you tried checking the exciter/regulator assembly? The TM's give a fairly simple procedure to test it.
That should narrow the problem to the exciter/regulator.

Otherwise you may have to start looking for broken wires, connection problems, etc.

Brian

Iwill have to go through the TM again. I couldn't find itI have the -12 is it in there? IF so can you tell me where?

I just received your PM. I'm looking it up now.

Brian

The information is in the TM5-6115-465-34 manual.

The instructions are on pg. 5-47 and the test layout is on 5-54.

I can email you the TM if you don't have it.

Brian

HEy I found the TM thanks for the info. Now I have to get some tools for the 208VAC and 95VAC