MEP-002A quit generating under full load. Where to start

[CrzyDave]

My genset quit on me in the middle of a power outage a couple nights ago. The motor struggled for a second, it stopped generating, then the motor recovered to full RPM with no output voltage. It starts right up now, but only outputs 1 vac.

Any help with how to troubleshoot would be very helpful. I found a mouse nest on the CT and CTI, but don't see any damage to anything in there.

I will test for DC battery charging this morning. I had to jump start the unit during the power outage, but once running it powered the whole house for a few hours before the failure.

Dave

 

[cuad4u]

"Engine struggled for a second.....then engine recovered to full RPM with no output voltage". This sounds like a current overload that the 5KW generator could not handle. Let's check the obvious and simple stuff first. Did the output circuit breaker trip? This is the main breaker to the left of the control panel. Turn it all the way off then flip it back in the UP position and see what happens.

 

[CrzyDave]

Thanks for the reply. I did try that, but it wasn't tripped. There is also no voltage at the auxiliary outlet.

I was just messing with it and found that if I hold the starter switch to start when the set is running, it outputs voltage to the outlet. I was doing this to reflash the magnetic field. I measured 5-6 VAC at the F+ and F- terminals while holding the switch in start, but 0 VAC when it is not in the "start" position. It was putting out 110 VAC, and the longer I held it went down to 108 VAC.

 

[CrzyDave]

I see that diode CR6 is a bit discolored/malformed. CR1, 2 and 3 seem to test ok, but CR 4, 5, and 6 all go to the same terminal on the board, and not sure what I should be reading if they are working properly without removing that board. It seems like the whole board is potted, so I can't probe it from the front.

Would CR6 have anything to do with loss of excitation? Thanks for any help.

 

[Isaac-1]

I am not an expert on these voltage regulators, but from what I do know it does not sound likely to be the issue. Most AVR board problems on these units tend to result in the voltage going high, not in field collapse.

 

[Triple Jim]

Which board are you talking about? Do you mean the regulator board or the diode board that supplies exciter field current?

There's a good schematic in the PDF file "TM5-6115-584-34.pdf" on page 1-9.

 

[CrzyDave]

I was talking about the diode bridge board, but I pulled it and checked all 6 diodes and the resistor. That was all fine.

 

[CrzyDave]

The regulator board looks ok. I see the bench test procedure in the manual, but it looks like quite a process. I think I have to pull it and two transformers and wire in two switches. I was hoping for an easier way to test it.

I know overload can cause field collapse. Is there some special way to re flash other than holding the start switch? I thought it reflashed at every start.

 

[Crabbie]

Unfortunately, there is not an "easy" solution to this. The issue could be many things from a damaged voltage regulator to a shorted stator, etc, etc, etc. If one looks at the symptoms that lead to this issue (generator under load that is working normally>then boggs down as it struggles to deal with a load>then comes back up to speed with no outut) a reasonable explanation although it may be wrong is that the genset shorted out causing the engine to bogg down until the short totally broke the circuit and the rpms came back up as the load went down.

A long story made short is get the multimeter and manual out and do some diagnostics. Replacing random parts will be very expensive, frustrating and in the long run futile.

I hope the field just needs reflashed, but don't get your hopes up. Good Luck.

 

[Triple Jim]

I was hoping for an easier way to test it.

Disconnect and insulate the wire that goes to terminal 17 of the regulator. This removes the regulator from the circuit. Then when you run the generator, you should get too high a voltage, like 170/340. If this happens, the regulator is at fault. If you still don't get any output, it's not because of the regulator.

 

[CrzyDave]

Thanks Triple Jim. I'll give it a shot. Luckily I have a couple parts gensets nearby where I bought mine. I just hope it isn't the actual generator head.

 

[CrzyDave]

I was reading an old thread over on ,smokestack and it was saying the exciter field should be getting 12vdc when holding start switch to start with unit running. I'm only getting 5, but it is generating while it is flashing. I guess this is a clue.

It is possible my voltage adjustment rheostat may have burned or something. It seems a little crunchy. Think that could cause this? I did adjust it an hour or so before failure. I guess I can test this with ohmmeter. I'll try it now.

 

[CrzyDave]

Voltage adjustment rheostat seems fine.

 

[cuad4u]

Voltage adjustment rheostat is wire wound and should read 0-1000 ohms as you turn the knob through its arc. I guess it can happen but I have never seen a voltage rheostat open up.

 

[CrzyDave]

TripleJim for the win!!!! Disconnected wire 17 at the voltage regulator and I have 165 VAC! I'll swap it out and keep everyone posted. I should be able to repair the old one, but it may test my skills...

 

[CrzyDave]

Cuad4u- I checked the voltage adjust rheostat and it was indeed 0-1k ohms

 

[Triple Jim]

I'm glad you found the problem. It's unusual for the regulator to fail in a way that prevents generator output, but if something on the board fails in a way that makes it get stuck fully conducting, that's exactly what happens... so much current through CVT1 that it kills the output.

 

[CrzyDave]

Ok. I'm will hopefully get the other board tomorrow. It looks just a bit different. The rheostats are a different form factor (long and rectangle vs mine that are small and square). I can't help but wonder if I should be testing the transformer and anything else in the circuit.

I don't see any damage to the board.

 

[CrzyDave]

And much thanks TripleJim and all others!

 

[CrzyDave]

TripleJim, I just read your classified add. Thats super cool! I may just do that. I'll see what happens with the test unit. They may want the same price for it or it might also be bad.