MEP803a Overload Fault Troubleshooting

[Haoleb]

Okay, I have been doing a lot of reading on this issue and I wanted to start one thread specifically about this issue for future reference for other folks with this problem as I go through diagnosis, troubleshooting and ... hopefully repair!

Here is the issue my set is having. When load banking the generator I have three water heater elements 4500w,4500w and 3500w. I can run one 4500w element with no issue. Ive ran it for about 1/2 hour with just one element. Then I switch on a second element. Be it either another 4500w or the other 3500w and the set runs for several minutes then trips overload fault. Last night I ran it with 8kw load and it ran for 8 minutes before tripping the fault.

My % Rated current meter seems to be displaying right on the money. With a load of 37.72A (when I was running 9KW) it was showing right about 72%. If I calculate 100% load to be 52A as it shows in the technical specs that comes out to 1.92% rated current per amp output at 240VAC. So 37.72A load calculates out to 72.42% which matches exactly my meter reading.

The engine of my generator does need to be run under load more as it will smoke somewhat with an 8 or 9kw load but for now I do not think that should be affecting anything since the fault circuitry is only going off of what the current sending circuitry is telling it. I have the schematics and have tried to figure out where to look if the gauge works properly and the rest of the circuit does not. Seems to lead me to the K8 Overload/Short relay that according to the schematic has three thermal devices (one per phase) that will trip out from current through the current transformers.

My next step is to troubleshoot the overload relay per TM 9-6115-642-24, Section 2-31

If it is faulty the Overload relay part number is 88-21141 which seems to also cross to P/N 19230 and there are several on ebay right now. If I do narrow it down to the overload relay I may just take it apart and try to repair it at the component level unless its all potted or covered in conformal coating. Another option i suppose would be to simply bypass the relay output for the overload side of this device. That way it would still trip on short circuit but not on overload.

Stay posted!

 

[lonesouth]

If it is faulty the Overload relay part number is 88-21141 which seems to also cross to P/N 19230 and there are several on ebay right now. If I do narrow it down to the overload relay I may just take it apart and try to repair it at the component level unless its all potted or covered in conformal coating. Another option i suppose would be to simply bypass the relay output for the overload side of this device. That way it would still trip on short circuit but not on overload.

I would rather fix than bypass. You know what the max load is, but what if you aren't home and the wife overloads it. Even if you have it run through a breaker that will pop at or around 125%, I think you'd be better off keeping the protection.

 

[Haoleb]

I would rather fix than bypass. You know what the max load is, but what if you aren't home and the wife overloads it. Even if you have it run through a breaker that will pop at or around 125%, I think you'd be better off keeping the protection.

I agree, especially since a NOS one is not too expensive at $60 and I like to have my gear work 100%... But, it could be done in a pinch if needed.

 

[lonesouth]

I agree, especially since a NOS one is not too expensive at $60 and I like to have my gear work 100%... But, it could be done in a pinch if needed.

In a pinch, he could run the battle short. granted this would bypass all safety features, and not just the one he know's is faulty.

 

[kloppk]

In a pinch, he could run the battle short. granted this would bypass all safety features,...

Almost all. The short circuit safety and the E-Stop still operate in Battle Short.

 

[Korgoth1]

I came across two units like this, they had out of spec current transformers. I removed two windings and they were perfect...

 

[Ray70]

Hi Haoleb, I'm very interested to follow your troubleshooting as I've got an 803A doing the same thing. I can run it at about 80% load for a few minutes then it trips the overload. So far I've unsoldered and tested the burden resistors and made some attempt at cleaning the AM/VM switch. My machine is a Letterkenny reset so I think I should check the wiring on the overload relay as well as the current transformer. Keep us posted on your progress!

 

[Guyfang]

Do not forget to look at the output load wires where they pass through the CT-1. Count the loops and make sure they are correct. Also, run the set at 5-6 KW for several hours. THEN step it up 1-2 KW and run it 1-2 hours. Continue till its maxed out. No gen set left my shop without a 100% load, for 6 hours. Granted, the army has the money to do that. But there again, I almost NEVER had someone complain or return a gen set to me.

 

[Ray70]

Fixed it! Turns out I had a dirty AC Reconnection switch. 1/2 can of contact cleaner and dozens or clicks back and forth and now it's working correctly. Loaded it up in stage like Guyfang suggests and now it runs at 125% all day long with no smoke at all. Next step is to advertise some of my generators and sell a few.... It's like an addiction but I really need to cut back a little...( so I can buy a 5 ton )

 

[Haoleb]

I have not had a lot of time to mess with It lately. I purchased a NOS current transformer off ebay just in-case since there was only one on there and for $30 shipped I figured what the heck. I got the top off the unit exposing the rear power box area and everything appears correct regarding the wires and turns through the CT. The CT also measures the same (no current going through) as the new one. Its just such a hassle to test the CT the way described in the TM I have not done that yet. I can't see how it could go bad over time short of having one of the coils go open or short. I did test the burden resistors and they were all good. I have a can of De-Oxit I suppose it would not hurt to clean out the selector switches with that stuff.

From a standpoint of my electronics and troubleshooting experience it seems hard to believe dirty contacts on a switch would cause it to fault on overload prematurely but I guess without knowing exactly how the circuit functions anything is possible.

I have loaded it up to 100% output no issues and ran it for a while.. with battle short engaged. Once I get this overload thing sorted I'm planning to just run it at 100% all day to give it a good workout.

 

[Guyfang]

I have not had a lot of time to mess with It lately. I purchased a NOS current transformer off ebay just in-case since there was only one on there and for $30 shipped I figured what the heck. I got the top off the unit exposing the rear power box area and everything appears correct regarding the wires and turns through the CT. The CT also measures the same (no current going through) as the new one. Its just such a hassle to test the CT the way described in the TM I have not done that yet. I can't see how it could go bad over time short of having one of the coils go open or short. I did test the burden resistors and they were all good. I have a can of De-Oxit I suppose it would not hurt to clean out the selector switches with that stuff.

From a standpoint of my electronics and troubleshooting experience it seems hard to believe dirty contacts on a switch would cause it to fault on overload prematurely but I guess without knowing exactly how the circuit functions anything is possible.

I have loaded it up to 100% output no issues and ran it for a while.. with battle short engaged. Once I get this overload thing sorted I'm planning to just run it at 100% all day to give it a good workout.

What happens when you have a loose contact? Dirty contact? Any type of connection that does not make proper contact, will cause heat. Same symtoms as an overload. Draws more amperage. An overload draws too much amperage, and when it exceeds the limit, pop goes the weasel. A loose connection will pass voltage, but amperage is another deal. I used to see this a lot with three phase underwater pumps. BIG ones. Happens. Seldom, but it happens.

I need to find the Tier 2 criteria, and see if S-8 is an automatic change item. I know the first round or two of Tier restes, the S-8 was not an auto change. A friend of mine who ran a Tier 2 reset shop told me that the S-8 was tested with a multimeter for continuity only. And everyone knows continuity is a liar, sometimes. Caused me many hours of false troubleshooting.

 

[Haoleb]

What happens when you have a loose contact? Dirty contact? Any type of connection that does not make proper contact, will cause heat. Same symtoms as an overload. Draws more amperage. An overload draws too much amperage, and when it exceeds the limit, pop goes the weasel. A loose connection will pass voltage, but amperage is another deal. I used to see this a lot with three phase underwater pumps. BIG ones. Happens. Seldom, but it happens.

I need to find the Tier 2 criteria, and see if S-8 is an automatic change item. I know the first round or two of Tier restes, the S-8 was not an auto change. A friend of mine who ran a Tier 2 reset shop told me that the S-8 was tested with a multimeter for continuity only. And everyone knows continuity is a liar, sometimes. Caused me many hours of false troubleshooting.

Hmm, I was focusing more on the wires from the CT itself going through a bad contact not the load wiring. I do see what happens with poor contacts on a regular basis replacing contactors that have had their contacts burned up which then creates so much heat it melts the insulation right off the wires connected to the lugs.

I'll focus more on cleaning and moving those switches around before I get too carried away looking elsewhere.

 

[Ray70]

Use the cleaner you have and spray it in from the sides of the switch at each wire connection. That seems to be the best place to get the cleaner into the switch. Work the knob back and forth rapidly while you're spraying in the cleaner. Mine was also showing erratic readings on the Load meter. Sometimes no reading, sometimes the meter would be pegged and sometimes it would read correctly. Sprayed contact cleaner into the open screw holes in the back end plate of the AM/VM switch, worked it around a bit, sprayed more... and more, then sprayed some more... and that fixed my gauge problem as well. My machine came from Kuwait and the inside of the control box had a thin layer of stuck-on dust on everything. I can only imagine what's inside the switches!

 

[Haoleb]

Well I have to say hats off to those who said to CLEAN THE SWITCHES!! because... you were so right.

The other night I put half a can of Deoxit into the reconnection switch and the VM/AM switch and worked them back and fourth several times. Today I had time to load bank the generator again and it ran at 9kw for longer than its ever run without faulting overload before so I ran it at 12.5KW for a full hour with not even a single hiccup. I'd say the last little problem I've had with this set is fixed!

I really didn't think it was something so simple but experience is more valuable than over thinking it every time, so thanks for the help!

 

[Ray70]

Now comes the fun part... step up the load in stages like Guyfang and others suggested. Go up a couple KW at a time and let it run till the smoke clears out, then step it up some more. You should be able to get it up to 16K or more indefinitely using resistive loads.