MEP-002A power problem

[Robtay]

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.

 

[Keith_J]

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.

 

[storeman]

Keith,
you astound me. Need a job?

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

 

[Keith_J]

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.

 

[Robtay]

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.

 

[Robtay]

More information:

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??

 

[R Racing]

Did you try exciting the feild ?

 

[Keith_J]

Did you try exciting the feild ?

Voltage is fine. This is a current issue. Check the breakers and all downstream connections.

If the voltage is constant without load, then dropping with load, it is most probably connection.

 

[Speddmon]

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.

 

[Keith_J]

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.

 

[PeterD]

...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??

1. First, you likely have a high resistance connection somewhere in your system. Could be a splice in the winding, but I'd guess it is external to the generator head.

2. No, it would not be the rotating diodes, they would affect both sides of the power equally.

3. I'd suggest careful resistance measurements. If a small load (that fish tank pump) of about 30 watts drops voltage to 30 VAC, the resistance will be significant. Somewhere, (off the top of my head) around 300-400 ohms to cause that effect. (120 ohms, at 120 volts, would give one amp of current, and 120 watts of power, you are at a third that, so three times that resistance.)

 

[Robtay]

I think I found it. I measured the output leads with my meter with the main breaker closed and got one that measured as open. I removed the main breaker and have one set of contacts that is not closing. It probably does close a bit with vibration, which is why I was able to measure any voltage at all. Anyone know where to get a new/used one?

 

[Speddmon]

Congrats on finding your problem, and I am glad you got lucky and didn't have a bad head. As to the breaker, they are available new, but you don't wanna pay the price for a new one (ouch). I have a few 002a output boxes complete if you wanna go that route. I would try one of the surplus places like Delks or Gulf Coast Trucks for a breaker.

After you get it fixed, stop hooking up that 1KW heater to the convenience outlet!!!!!!

 

[Wildchild467]

I learned a lot from this thread. When i was reading it, i was thinking it was a bad connection. I am not an AC voltage guy, but it makes total sence what happened.

Would any kind of additional PMing not in the TM have helped reduce this kind of problem? Speddmon, i know you mentioned something before about the 3-position switch and lubricating that because it was not working right for somebody? im not saying lubricate everything and go crazy (even though, i did lube all the hinges, and linkages on my MEP-002A), but a respectible attention to detail and inspection so that everything contunes to operate as it should.

 

[Speddmon]

I don't think there is anything outside of the TM's that you would need to go out of your way to do. As far as lubricating the re-connection switch, I suggested that to a member who had one that was frozen in place from lack of use.

What I would recommend everybody do, is to rotate the re-connection switch through all three positions while you are holding the master switch in the preheat position. That way it gets some exercise and doesn't become bound by corrosion and rust like a lot of them do from lack of use.

 

[storeman]

Tom,
What does the preheat position on the master have to do with rotating the phase switch for exercise? I don't understand.
Jerry

 

[Speddmon]

Since you are supposed to be in preheat for 1 minute before starting the generator, use that free time to rotate the reconnect switch. You DON'T switch it under power, so while you're sitting there with your hand on the preheat switch, why not make some good use of the other hand and do a little preventive operation.