My MEP-803a experience

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lonesouth

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I went through troubleshooting 2-27.2 for the Voltage Regulator. Everything checked out except voltage adjustment potentiometer. On the generator on the stand, I got 4.85kohm max, and 4.89kohm max on the second generator. They were both consistent in stopping at those figures. Is the 150 and 110 ohm short from 5k sufficient to drop the voltage from 240 to 210?

I see that there is a voltage regulator adjustment rheostat. It is mentioned here regarding a MEP-002a with a similar issue, but I wanted to get some feedback on the voltage adjustment pots being short of 5k before I go tinkering with the voltage regulator.

Incidentally, the test requires checking voltages with the master switch in the start position. In that position, the output was the full 240v.
 
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lonesouth

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not yet, beyond plugging a fan into the convenience outlet. I was concerned that a load might somehow amplify the voltage issue or damage other components if something were wrong. I'm also trying to not start them too much until I get the fuses and holders in for the quad winding modification.
 

Guyfang

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I went through troubleshooting 2-27.2 for the Voltage Regulator. Everything checked out except voltage adjustment potentiometer. On the generator on the stand, I got 4.85kohm max, and 4.89kohm max on the second generator. They were both consistent in stopping at those figures. Is the 150 and 110 ohm short from 5k sufficient to drop the voltage from 240 to 210?

I see that there is a voltage regulator adjustment rheostat. It is mentioned here regarding a MEP-002a with a similar issue, but I wanted to get some feedback on the voltage adjustment pots being short of 5k before I go tinkering with the voltage regulator.

Incidentally, the test requires checking voltages with the master switch in the start position. In that position, the output was the full 240v.

I find it hard to believe that both sets have the same problem. Having said that, take a look at the part numbers on the R-1 volt adjust rheostats. Compare the part numbers, with the part numbers in the parts TM. If both sets were "fixed" or sent to Tier 2 at the same time, (makes sense) then maybe someone put the wrong R-1's in the sets? You never know. Seen it happen before, with other parts.

Did you ever see the sets run right before?

I can not answer your question, " Is the 150 and 110 ohm short from 5k sufficient to drop the voltage from 240 to 210?" I am not sure. I do know that we had a bad batch of volt regs come out in 2009, and the quick fix was to adjust the pot on the volt reg to compensate for it. And we were not to do it ourselves, but to let a CECOM Rep do it. Nonsense of course. Check the part numbers first, something stinks here. Coincidence, is always suspicious. Also, did you check the R-1's with the wires disconnected?
 

lonesouth

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Location
Tallahassee, FL
I find it hard to believe that both sets have the same problem. Having said that, take a look at the part numbers on the R-1 volt adjust rheostats. Compare the part numbers, with the part numbers in the parts TM. If both sets were "fixed" or sent to Tier 2 at the same time, (makes sense) then maybe someone put the wrong R-1's in the sets? You never know. Seen it happen before, with other parts.

Did you ever see the sets run right before?

I can not answer your question, " Is the 150 and 110 ohm short from 5k sufficient to drop the voltage from 240 to 210?" I am not sure. I do know that we had a bad batch of volt regs come out in 2009, and the quick fix was to adjust the pot on the volt reg to compensate for it. And we were not to do it ourselves, but to let a CECOM Rep do it. Nonsense of course. Check the part numbers first, something stinks here. Coincidence, is always suspicious. Also, did you check the R-1's with the wires disconnected?

I did check the R1s from lug 2 on the A1 to the wire removed from lug 1 on A1. I'll get a look at the part numbers on R1 when I get home.

I checked the voltage on both sets, when they were both still installed on the power plant trailer, when that trailer was on my equipment trailer. I also verified voltage a few days prior to removing the generators from the power plant trailer, on one of the generators with a killawatt.

The only other thing I observed is that the voltage between F1 & F2(terminal 5&6 on A1) was slightly less than 8v, but the TM says approximately 8V, so I did not think to mention it.

Do you happen to have the schematic for A1?
 

Guyfang

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See, this is the part that I feel is "strange". If it worked before, why not now? And both sets?


I checked the voltage on both sets, when they were both still installed on the power plant trailer, when that trailer was on my equipment trailer. I also verified voltage a few days prior to removing the generators from the power plant trailer, on one of the generators with a killawatt.

I have seen the Static Exciter light off with 3 volts, so approx 8 should be good.

The only other thing I observed is that the voltage between F1 & F2(terminal 5&6 on A1) was slightly less than 8v, but the TM says approximately 8V, so I did not think to mention it.


The manufacture doesn't like to give the military all the schematics anymore. I will ask someone I know, but no promises. He doesn't need the problems associated with "dealing with outsiders", and I don't need the problem of asking him to compromise himself.


Do you happen to have the schematic for A1?[/QUOTE]
 

lonesouth

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that was for me :)

I've been staring at the schematics for a little while. This may be a bit of stream of consciousness...

When running normally, the voltage regulator will vary the resistance across pins 5&6(the exciter stator) which will control the magnetic field produced by the exciter stator, which will control the AC volts generated by the exciter rotor, which get rectified by the F1 and F2 diodes creating a DC voltage that excites the main rotor, which controls the magnetic field affecting the main stator, which creates the AC power presented to the output lugs.

The quad winding is used to provide power to the voltage regulator pins 7&8, nothing else.

The sense pins, 3&4 pickup the voltage output from the generator on outlut lugs L3 & L0. These are not run through any circuit breakers or switches.

The voltage adjustment pins 1&2 connect to the voltage adjustment potentiometer pins 1, 2, & 3.

When the voltage regulator senses high impedance from the voltage adjustment pot, it decreases impedance(increased current) to the exciter stator until the voltage sense aligns with the expected voltage. When low impedance is detected, higher resistance is applied to the exciter stator.

So: if the stator outputs are within spec, and voltage output is lower than expect, then one of the below situations is present:
1. the impedance detected from the voltage adjustment pot is lower than required
2. the resistance applied to the exciter field is higher than required
3. the base voltage value that the sensed voltage is compared to is lower than it should be

1. can be checked by adding a resistor in line with the voltage adjustment pot to increase the resistance at the voltage adjust pins of the voltage regulator, or by replacing with a known good(0-5k) pot
2. is internal to the VR and can not be determined at this time without a schematic of the VR
3. is probably controlled by the VR adjustment pot

When the master switch is set to start, 24VDC is sent to R14-Field Flash Resistor(50 ohms) resulting in ~.5amps which passes through a diode to exciter stator. Since this does cause the output to elevate to above the standing voltage with the voltage adjustment pot set at max, I believe the exciter stator, main stator, exciter rotor, main rotor, and rectifying diodes are operating as they should. When the master switch is released, the field flash circuit is bypassed and the voltage regulator takes over. The quad winding was observed to be in spec, so I expect that to be OK as well.

again, this is me thinking through how the generator functions and what impacts what.
 
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lonesouth

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i put a 220 ohm resistor in series with the pot to get 5kohm exact. That gave me an output voltage of a little more than 220. The only thing I can think of, is that the voltage regulator has drifted, as a result of the bumps while unloading from the trailer.

right or wrong, I adjusted the voltage regulator pot. clockwise decreases voltage, counter clockwise increases the voltage. I got it where 240 was right about the middle of the adjustment range. So, for one of them, I have it "fixed" though I still have not put a real load on it, yet.
 
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