New to me PU798A (Mep-803a on a LTT-TQG high mobility)

[DieselAddict]

3 phase is the standard in industrial/commercial installations. You have to pay a premium to get 3 phase in a residential install. I see it occasionally. For most that have a shop at their home they are stuck with single phase unless they want to pay a lot more for 3 phase service.

 

[Ray70]

Yes, its a single phase compressor. From what I read from others it seems my MEP-003A is better suited to running the compressor ( if the need should ever arise ) than the 803a's. The -003A will start it and run it, but the 803A does exactly what AOR said. It bogs down, chuggs and smokes with the %gage pegged. Apparently ( like others have said ) the -003A has more reserve power than the 803A.
To get back to the issue at hand, I now have one of the units running perfectly. Stepping up the load gradually now has it running at 120%+ indefinitely and 133% for 15 or so minutes before the overload trips, so that one is good to go.
I didn't do the math as far as percentages go, but by adding up the advertised load of everything I had running it should be 13,850 watts!
I've got a copy of the TM and will soon start looking into the other unit that trips the "Short Circuit" light after about 70% load. Note: I'm using the same resistive load as I used on the other machine so I'mm 100% positive its not a short circuit, its a problem with the warning lights on the genny.
Hopefully I'll get a chance to work on it this weekend!
Thanks everyone...

 

[Guyfang]

Ray,

To test your theory about the Short Circuit/Overload Relay, go to work package 029, in the TM 9-6115-642-24 manual and work through it. As you have a known good set, you can control substitute the relay, and the fault indicator.

 

[Ray70]

Thank you Guyfang. I'll hopefully be able to work on it this weekend. I did a little bit of testing on it last night and found that if I increase the load slowly using purely resistive loads the overload will trip at about 70%. If I apply a large load all at once it throws the short circuit light. Looking at the theory of operations it seems that the machine is probably thinking it is being grossly overloaded ( possibly because of 1 or more bad resistors ) such that it see the overload condition as a short circuit. I looked behind the control panel and one of the large resistors had a white powdery mark on it, like one of them cooked itself, so I'll be testing them this weekend. But now it seems that I've lost my % load meter... I was exercising the selector knobs a little to see if there was any corrosion on the contacts, next thing I know the load meter is no longer working. I was exercising the knobs with machine running but AC circuit interruptor open.

 

[Ray70]

So I got a chance to work on the 803A a little today. Seems like my % load meter not working was caused by poor connections in the AM/VM switch. Seems to be working again now.
As for the overload tripping too soon, I unsoldered the wires from the burden resistors and they all tested good. Next step is to open it up and check the windings through the Current transformers. If that checks out I'm going to go back and further investigate the AM/VM switch and AC reconnect switchs for high resistance connections, unless you guys have any other suggestions??

 

[DieselAddict]

I would troubleshoot all the switches first. That is where the wear or corrosion is going to take its toll first.

 

[Guyfang]

Also check to see that CT1 is wound right. Count the number of times that the load wires pass through the CT, then check it against the schematic.

 

[Ray70]

It was the AC reconnect switch, cleaned it out with contact cleaner and now it working perfectly! thanks everyone!

 

[Joe Drifter]

Hey guys,

I'm a noob here. I just picked up a MEP-803a with the aluminum trailer. Someone stole the start switch off of it. I purchased a new one but not sure where what goes where. Can someone help me find a diagram or something? Also I purchased it as an inop so it didn't run. I changed the oil and drained out the tank. Anyone in GA with one of these? Thanks

 

[DieselAddict]

Hey guys,

I'm a noob here. I just picked up a MEP-803a with the aluminum trailer. Someone stole the start switch off of it. I purchased a new one but not sure where what goes where. Can someone help me find a diagram or something? Also I purchased it as an inop so it didn't run. I changed the oil and drained out the tank. Anyone in GA with one of these? Thanks

The best thing to do is to start your own thread. If you go to the top of the screen on the forum there is a link for "Technical Manuals". You can go to the generator section and find the technical manual for your machine. There will be wiring diagrams in there.

You can see a cleaned up version of the schematic here - https://drive.google.com/open?id=0B2ucd1TGFTw_b0dqdURiS3lOZlU

 

[Guyfang]

Yes a new thread helps us keep things straight. This won't be hard. The switch is easy. Don't forget to post the part number/NSN of the switch you bought.