I have an MEP-002a that has a power issue. I've been testing it periodically and putting a 1kw heater on the convenience outlet to load it. Yesterday I decided to hook it up to the house using my transfer switch and a cable, which has worked fine in the past. The switch on the generator is set for 120/240 Vac, which allows me to run my well pump. When I hooked it up, I only had power on one of the 120 VAC legs. The other leg read 40 VAC with my meter. If I pull the plug from the transfer switch, I read 120/240 at the plug, so it only does this under some load.
So where should I start? Voltage regulator, switchbox, or diodes? Thanks in advance for any help you can provide.
If the voltage is fine in the other leg, the problem is that winding or connection. By meter, I assume you are talking about a verifiable hand-held meter, not the panel meter. If so, the problem is likely in S6, the reconnection switch. It cannot be the voltage regulator as this controls the field which is turning at 1800 RPM and cannot vary fast enough to drop the voltage in one leg.
I would disconnect the generator from all loads and test the output voltage in all three connection positions of S6, starting with 120 V 2 wire single phase. I would suspect either S6 has a bad connection or one of the screw terminals is loose. Take the cover and terminal board off to check every lead WITH THE GENERATOR OFF!!! Any time you have the cover off, disconnect the battery negative cable. While inspecting, verify the jumper wire from S6, terminal 6 to L0 has been installed. This is change 6 in the -12 TM but only pertains to operation in 120 V 2-wire mode.
The convenience receptacles should never be used for testing with any significant load. Only very minor loads should be connected. Get a length of 10/3 and hook up a NEMA 5-20 receptacle for testing with a load bank, using the 120 V 2-wire reconnection of S6. This way you have accurate panel meter readings. About the only load I recommend from these outlets is a trouble light or two. Not 1000 watt loads, ever. The circuit breaker is only there for protection of the wires, it is not an implied maximum load.
When I get a chance, I'll come at you with a history on a Mep-002a and would appreciate your insight. Believe I recall you ran a generator maintenance section. As an officer (and implicitly speaking for most officers) I just went past our generators in the artillery motor pool and nodded because I knew absolutely nothing about them. Now that I'm down to the pistons, I am still clueless.
Jerry
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M101A3
MEP-002A 10 on hand!
Two to keep, 2 ready to sell.
Two being worked on.
Four being parted out.
I'm 100% self-taught on power generation and repair. I did manage to acquire course work materials from the school, enough to enable me to pass the MOS (then 52D) exams far above Army averages at that time.
It helps that I also have a degree in mechanical engineering.
Thanks for the information. I opened up the connection box and found a couple of loose connections.
Hopefully when I get it put back together it works.
I tightened up the loose connections in the connection box and reassembled it to the generator. I started it up and mesured with my meter 120 VAC from both hots to neutral, and 240 vac between the hots. So I powered it down and hooked it to a portable power panel. when I started it up I measured again at the panel and got the same. I plugged a 120 VAC portable heater into the panel and the generator loaded down like I would expect. When I plugged it into a plug using the other half of the split phase power, there was no change in the generator sound. I measured again with my meter, and the voltage was now at 0 Vac under load. I then plugged in a very small load (a fish tank pump) and the voltage sagged from 120 Vac down to 30 Vac. So now I'm thinking rotating diodes. Sound correct??
It's not the rotating diodes. If they were the problem you wouldn't get anything at all. You need to get someone with a current HI-Pot and check the generator head.
Using a 1KW heater at the convenience outlet you were creating quite an unbalanced situation on one coil of the head. My guess is that you have a bad coil now (guess which one). I've seen situations like this in the past on other equipment...you can measure voltage but as soon as you start pulling current, the connection opens up and then the voltage finally drops. Take away the current and the voltage comes back.
Without seeing it and checking things for myself, I would say you have a bad coil. If you are running in 120/240 mode all the time, you could probably rewire the cannon plug to use the "free" coils to get it back again if that were the case.
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Get the -34 and check stator winding resistance. Sounds like there is a shorted coil. Check the wiring diagram to see which winding the convenience outlet is connected to, that will probably be the shorted coil.
I wouldn't recommend reconnecting the stator windings to put this winding on the high side with the reconnection switch in 120/240 since this will only additionally load another winding.
If the resistance of this winding is low (like 0.10 ohms or less), the problem MIGHT be repairable by cleaning and revarnishing. But if the problem is an open, only rewinding will work. Your best bet would be to find a generator with blown engine.
Let this thread be a reminder that the NEMA duplex 5-15 outlet should only be used for a single drop light or possibly a small appliance. Never anything over 500 Watts and never for a steady load. It is connected to T3 and T6.
MEP-002A power problem
