MEP 002A Control box issues

[ClintA]

Fist off I hope I am not beating a dead horse, if so I will take my butt chewing. I always try to win at least 2 gensets so I can try to make one good one. I picked the best out of the 2 latest ones I won and got her running. When I first started it it was overcharging voltage big time, 1st thought was Voltage Reg so I got a new one, then Gen decided not to run, Changed out the heat censer and runs like a Champ. But now no power to Control box, so I take Control box off other set and back to square one, over charging big time with new Voltage Reg. Makes me think nothing was wrong with original Voltage Reg? I get the same Volts even when I try to turn it down with nob. My guess it is the main switch inside the Control Box on both units are fubar, but perhaps I am missing something? Thanks in advance, Clint

 

[Triple Jim]

You said "overcharging", which implies it's overcharging the 24v battery, but then you said you tried to turn it down with the knob, which makes it look like you mean the AC output is too high. What voltage are you getting?

Is the control box that you swapped the one with the meters on it?

 

[jamawieb]

Make sure you verify the voltage with a volt meter. I had a unit with a defective gauge and I was troubleshooting everything until I realized the gauge was bad and reading 300+ volts.

 

[ClintA]

You said "overcharging", which implies it's overcharging the 24v battery, but then you said you tried to turn it down with the knob, which makes it look like you mean the AC output is too high. What voltage are you getting?

Is the control box that you swapped the one with the meters on it?

I am not sure what the box is called, but it is the one that the wires hook too, the cubicle left of the battery slave. I get 320 volts where I should get 240 and I get 160 volts where at the 120 volt plugs. Thanks Jim

 

[cuad4u]

I have a problem understanding exactly what is your problem. Assuming the wiring is OK it sounds like either your AC voltage regulator or the voltage adjustment potentiometer is bad. Not ALWAYS running the engine at rated RPM and / or excessive idling at startup or shutdown can cause the AC voltage regulator to fail. Many AC voltage regulator failures are due to transistor Q4 shorting or opening. That transistor is readily available and is easily replaced if you know how to solder.

 

[ClintA]

With the original AC output control box I get no volts to speak of and no HZ and when I put on the AC output control box off the other gen set I get 320 volts on top and 240 where the plugs are for power tools. I will check Q4 and see what happens?????

 

[Triple Jim]

Make that Q3. There is no Q4 on the AC regulator board.

This generator, and the 003A, use a special transformer, CVT1, to control the exciter field current. When the output voltage is too high, the regulator supplies current to the control windings of CVT1, causing it to reduce exciter current, which reduces the generator output voltage.

This means that if the generator output voltage is too high, one several things could be causing it:

1. As cuad4u said, the AC regulator may have failed, and is not sending current to CVT1
2. As cuad4u said, the front panel adjustment pot or the wiring to it may have failed, and as a result, the regulator thinks the generator output is too low and raises it.
3. Although it's unlikely, CVT1 may have failed, and isn't controlling the exciter current. The resistances of the windings of CVT1 are in the TM, so they can be tested with an ohm meter.
4. Wiring and/or connections in the circuits related to the above could have a problem.

Note that running the generator below its rated speed of 1,800 rpm tends to reduce the generator's output voltage. This will cause the regulator to reduce its output to CVT1, not increase it, in an attempt to raise exciter current an bring the voltage to 120/240. Although Q3 and other parts of the AC regulator do sometimes fail, running the generator below 1,800 rpm actually lightens the load on the regulator, and isn't likely to cause any harm.

CVT1 is in the enclosure below the output lugs, and is one of two large black enclosed transformers with multiple terminals, and big wires passing through them.

 

[ClintA]

Jim, I had time to work on the gen set this afternoon, I changed out T2 and with the original AC Control box I still had nothing, I put the AC box that I was getting high volts back on and all is fine now (240/120). So I think it was T2 that was part of my problem and the original AC control box is fubar. I have not tested it under load for I ran out of daylight but I bet it is all good now or I hope anyway? The original AC control box, I could not get any volts out of it no matter what Phase I put the switch on so I think it was or is the main switch? I am not that handy at trying to figure out what is wrong with it, I am not sure even where to start? ( lots of wires in there haha) That is why I try to win at-least 2 each time. Thanks so much for your help and your Voltage regulators, Clint

 

[Triple Jim]

You're absolutely right at T2 being another possibility when the generator output is too high, I should have mentioned that. I'm glad you knew to check it. The regulator senses generator output voltage after being transformed down by T2, so if that transformer fails, the regulator thinks the generator output is low and raises it all it can (by not sending any control current to CVT1).

Edit: Also note that if T1 fails, there's no power for the regulator board itself, so it can't control CVT1, and the generator output will go high.