MEP802 Short

[98G]

I read through the troubleshooting portion of the -10 and didn't see this explained.

Here's what I've got:

MEP802 340hrs , runs fine when set to 208 3phase. Runs fine when set to 120v single phase. Convenience outlets work fine in both positions. No fault lights. Gauges wnl.

Copious black smoke and irregular loping, fails to reach normal operating rpm when set to 120/240v single phase. "Short circuit" light illuminates.

Nothing connected to the lugs. Contactor open.

What do I need to look at in more detail?

(This is not the machine that I had previously connected to the house.)

 

[Ray70]

When in 120/240 mode is sounds like there is something causing a short/overload and lugging the engine to the point that it's bogging down.
First thing I would do is remove the top cover to expose the AC select switch body and the 12 wires coming out of the generator head going to the terminal strip.
I would clean ( with detoxit spray ) and exercise the AC select switch heavily incase something is hanging up internally.
I'd also check the wiring to see if you have a wire on the terminal strip or a wire on the AC select switch in the wrong spot.
Also check for wires chaffed against sheet metal edges etc.
This is not the kind of failure you are going to find a solution to in the TM. Gonna have to track it down yourself.

 

[98G]

When in 120/240 mode is sounds like there is something causing a short/overload and lugging the engine to the point that it's bogging down.
First thing I would do is remove the top cover to expose the AC select switch body and the 12 wires coming out of the generator head going to the terminal strip.
I would clean ( with detoxit spray ) and exercise the AC select switch heavily incase something is hanging up internally.
I'd also check the wiring to see if you have a wire on the terminal strip or a wire on the AC select switch in the wrong spot.
Also check for wires chaffed against sheet metal edges etc.
This is not the kind of failure you are going to find a solution to in the TM. Gonna have to track it down yourself.

I'm absolutely certain it's something that's only involved when 120/240v is selected, and absolutely certain that the bogging down is caused by overload.

You can see the load gauge in pic 1 showing it's completely unloaded. Pic 1 is when 208v 3phase is selected and it's running well. In pic two the load gauge is pegged and it's bogged down.

So i guess what I'm looking for is a list of things that are only used in single phase 240v, and you've given me that. Greatly appreciated! When I figure it out I'll post the details of what and where it was.

Worst case, I can keep 208v 3phase selected and split out each leg to 120v single phase or combine two legs to 208v single phase to run my welder. But I'd prefer to find and resolve it and have it running as intended.

Thanks again.

 

[Chainbreaker]

So AC breaker is not tripping when you are in single phase 240 & bogging down?

Regardless of whether if it trips or not, I agree with Ray, I would take both the top cover and the side cover off & closely inspect inside the box. I had a mouse get inside one of mine & wreak havoc but my box was DOA as far as electrical output after that.

Hopefully it's not a gen head related problem.

 

[98G]

No breakers tripping. I'll pull the cover off and eyeball it tomorrow evening and report back.

 

[Guyfang]

Thats the best place to start. Might be mouse damage there too.

 

[kloppk]

If no mouse issues or chaffed wires then I'd highly suspect one or more of the contacts in the Phase/Voltage switch are welded closed. Each switch contact relies on a tiny spring to open the contacts.

 

[Light in the Dark]

I believe your issue will lie in where all have said above... inside the operator box, related to either the S8 or its accompanying wires. My gut tells me its the switch, just for the fact that the other settings work fine... I don't believe its the head. Good luck in the hunt.

 

[Denvercaitland]

Should it be S8 or related to S8 as mentioned above. I suggest you do a very thorough visual inspection of S8. I had a S8 failure on my 803a which led to a "fried" Stator . As you can see from the Pics , the S8 failure was not obvious with the switch in the 803a and all wires connected. Even on the workbench the external clue where nothing compared to the internal damage.

 

[Denvercaitland]

Should it be S8 or related to S8 as mentioned above. I suggest you do a very thorough visual inspection of S8. I had a S8 failure on my 803a which led to a "fried" Stator . As you can see from the Pics , the S8 failure was not obvious with the switch in the 803a and all wires connected. Even on the workbench the external clue where nothing compared to the internal damage.

I should add, that the set was running fine and would run at full load . The only symptom was that the 803a would randomly " bog down" as if large additional load was suddenly applied. ( That is before the S8 failure fried the stator.. and the set died ).

 

[98G]

Today it has new symptoms.

Bogging down severely with the short circuit light illuminated in either of the single phase positions if the position is reached by turning the switch clockwise.

But I can turn it counterclockwise from the far right position to the middle position and it runs fine. But no power at the convenience receptacles.

Runs fine and behaves normally when 208v 3phase is selected. Convenience receptacles work fine.

I removed the half million bolts holding the cowling on and got eyeballs on the wires behind the phase switch. Nothing overtly damaged, but the presence of a couple of walnut shells speaks to the visitation of rodents.

I looked at the wires inside the two doors under the control panel. No overt damage.

I'm inclined to think it's internal to the phase selection switch. But I'm neither an electrician nor a generator tech. Are these switches readily available? I'm not above diagnosis by parts substitution....

Next question. Any reason I can't test voltage with the door open and the genset running? I'm inclined to test voltage on each of the 3 legs to neutral with it in the 208v position... but the "high voltage" warning on the door gives me pause.

Here's pics from today -

 

[Guyfang]

The thing in the middle is K1. Take the black safety cover off. remove the big wires on the right side. Tape em off. Start the set and flip the AC circuit breaker switch on. Same thing happen?

 

[Guyfang]

Yes you can leve the door open. Just dont stick your knob dickers where they dont belong.

 

[Light in the Dark]

Have you deoxidized any of the contacts in this switch, or any other switch/relay/terminal connection in the machine?

 

[98G]

Have you deoxidized any of the contacts in this switch, or any other switch/relay/terminal connection in the machine?

I haven't. I did nothing more than check fluids and slave it from the hmmwv and check power at the convenience outlets. All was fine (it was set to 208v 3 phase).

This was the 3rd of three sets. After the other two were tested and sold, I turned my attention to this one with the results posted here.

I'm learning. I appreciate the teaching.

 

[98G]

The thing in the middle is K1. Take the black safety cover off. remove the big wires on the right side. Tape em off. Start the set and flip the AC circuit breaker switch on. Same thing happen?

View attachment 909073

Thanks! This will be tomorrow's activity.

 

[flyfishtrailer]

Today it has new symptoms.

Bogging down severely with the short circuit light illuminated in either of the single phase positions if the position is reached by turning the switch clockwise.

But I can turn it counterclockwise from the far right position to the middle position and it runs fine. But no power at the convenience receptacles.

Runs fine and behaves normally when 208v 3phase is selected. Convenience receptacles work fine.

I removed the half million bolts holding the cowling on and got eyeballs on the wires behind the phase switch. Nothing overtly damaged, but the presence of a couple of walnut shells speaks to the visitation of rodents.

I looked at the wires inside the two doors under the control panel. No overt damage.

I'm inclined to think it's internal to the phase selection switch. But I'm neither an electrician nor a generator tech. Are these switches readily available? I'm not above diagnosis by parts substitution....

Next question. Any reason I can't test voltage with the door open and the genset running? I'm inclined to test voltage on each of the 3 legs to neutral with it in the 208v position... but the "high voltage" warning on the door gives me pause.

Here's pics from today -

If the selector switch is the same one used in an 803 a I may have a NOS one in my garage. Let me know and I can go dig to see if you need it.

 

[Guyfang]

Its the same. There is an old and new type. But they are the same internally.

 

[98G]

Thanks! This will be tomorrow's activity.

Disconnecting K1 from the switch didn't resolve it.

 

[Guyfang]

So the next step is to remove the wires on the other side of K1, tape them off and try again. That way you know if its in the K1. Or take the K1 out and take it apart. Could be full of water. Could have a an internal problem. If the K1 is good, then its trace the wires back to the S8. . Look for a place its shorted out. If no wire problems, I would remove the S8 and test it IAW the TM. Something else you could do is pull the end cover off the main gen, look inside, for burn marks or damage. And then test the main gen IAW the TM. Less work then taking the S8 out. My gut feeling is S8. BUT, you have got to insure that no wires are damaged and shorting out to one another or the frame.