MEP 002A generator exciter issue.

[herbertv2]

I have a Libby MEP 002A 5Kw generator. I'm having issues getting it to generate power, when you hold the start switch in the start position to excite the field the generator makes power fine, soon as you release the start switch it quits making power. What would cause this issue?

 

[jamawieb]

If it's making power while in the start position, the problem most likely will be found in the distribution box. Their is a control board inside (I believe it's A2 or A3)that is mounted on the backside of the distribution box. There are several capacitors on the board that maybe the problem.

 

[Triple Jim]

Generally, when you hold the switch in the "start" position, the control circuit is wired to apply 24v from the battery through a resistor to the exciter field to get the generator making power. Then when you release the switch, the regulated exciter current should take over. This is produced by CVT1 (large black transformer in box under output lugs) sending 3-phase AC to a rectifier board near it, making DC, which then goes to the exciter field. This current is regulated by the AC regulator board in the main control cabinet. It regulates by sending current through special windings in CVT1 that reduce CVT1's output current to the exciter. (more regulator output = less AC generator voltage out)

Something is causing this system to fail, and not supply exciter current after you let up the start switch. CVT1 could be bad, the diode board could have bad diodes, there could be broken wires or corroded connector pins, or the regulator board could have failed with its Q3 (output transistor) shorted. I'm sure I haven't thought of all the possibilities, but you should be able to use the schematic in figure 1-1 of TM5-6115-584-34.pdf to trace things through and find the problem.

The TM also has a troubleshooting section, and a paragraph that gives the resistances of all the windings of CVT1.

 

[herbertv2]

Well I tore into it some this week, I noticed on the Diode board the Resistor on the bottom of the board is burnt. Also noticed where the wires loop around the CT1 and CTV1 transformers the wire closest to the engine appears to have gotten hot at one point where it goes through the transformers looks like the are slightly browned.

Was talking to the guy that last ran it, it was used in a strip mine to run the block heaters on a d10 bulldozer in the Winter, they came in one morning and smoke was pouring out of the distribution box though it was still generating power at the time. But they shut it down and put it in storage.

So the unit wasn't overloaded, the block heaters would have ran it at a little less than 50% capacity.

I haven't had a chance to test the transformers yet, spent about an hour figuring out which terminals were what, and went to test them t find my mulimeter was broke.

 

[Triple Jim]

The resistor on the diode board is the one that's in series with 24VDC during starting. The overheated wire through CVT1 points to a problem with CVT1, I'd think. It's probably worth measuring the winding resistances and comparing to the specs in the manual.

 

[herbertv2]

Well I tested CTV1 and it was way out of tolerance, would seem it has failed. CT tested out fine, recommended course of action? I can't seem to find anywhere that has a CTV1 transformer

 

[Triple Jim]

Delk's Surplus, possibly. I found one that a member here had for sale. You could try posting that you're looking for one. I'm sure it was just a typo, but you're looking for CVT1.

I'm curious about the failure. Was the C1-C2 resistance off? What readings did you get?

 

[herbertv2]

c1 to c2 8.3 ohm
h1toh2 0.5 ohm
h3 to h4 11.4 ohm
h5 to h6 2.6 ohm
x1 to x2 1.8 ohm
x1 to x3 1.8 ohm
x2 to x3 1.8 ohm

I'm considering converting it over to an AVR 460. Also is there any easy way to get the CVT1 transformer out ?

 

[Triple Jim]

You could certainly do the SX460 conversion. There's a recent thread or two that guys who have done it started. One is by Rustystud.

I don't know of anything easy about working on CVT1, unfortunately. If I change mine, I'm going to label every wire with the terminal it goes to, and carefully note the number of turns the big wires make through the transformer holes, and which holes they go through, and go to it.

 

[jamawieb]

Well I tested CTV1 and it was way out of tolerance, would seem it has failed. CT tested out fine, recommended course of action? I can't seem to find anywhere that has a CTV1 transformer

There is someone on the big auction site that has a brand new CTV1 for $212 or best offer.

 

[Bill W]

c1 to c2 8.3 ohm
h1toh2 0.5 ohm
h3 to h4 11.4 ohm
h5 to h6 2.6 ohm
x1 to x2 1.8 ohm
x1 to x3 1.8 ohm
x2 to x3 1.8 ohm

I'm considering converting it over to an AVR 460. Also is there any easy way to get the CVT1 transformer out ?

Or instead of buying a generic VR you could buy a custom made one from Triple Jim

http://www.steelsoldiers.com/showthread.php?141621-AC-and-DC-Regulators-for-the-MEP-002A-and-MEP-003A

 

[Triple Jim]

I appreciate that, Bill, but the one I make is a replacement for the original one, which requires a working CVT1. In herbertv2's case, his CVT1 failed, and he's considering rewiring of the system for an SX460 regulator. That regulator doesn't use a magnetic amplifying transformer (CVT1), but rather supplies exciter current directly like most conventional generators do.

 

[Bill W]

Ooops my bad!!

 

[Triple Jim]

No problem at all, easy mistake, and thanks for the recommendation anyway.

 

[herbertv2]

Well I finally got into tearing it apart, when I pulled CVT1 not only did it not pass the checks, it had clearly melted down and burnt up on the end marked A so found where the smoke I was told about was coming from. Also got my 460SX AVR and prepping it to install, planning to do away with the switch for changing phases and hard wiring it for 220 single phase, only, have no need for 3 phase. I look at it this way the simpler it is wired the easier it is to work on next time.

 

[justacitizen]

Rustystud has a thread on a similar conversion. he has some schematics and photos also. will you document the process and take photo schematics etc?

 

[herbertv2]

Rustystud's conversion is the one I'm following and I can take pics. Will likely be adding a set of digital gauges, and likely updating the filters to the spin on style someday soon. Briging the old girl into the 21st century lol

 

[Guyfang]

Herbertv2,

Really, that's the only thing the military should have done. Keep the engine and main AC, upgrade the electrical portion. The engine and main AC were simply outstanding.

 

[Triple Jim]

The 002A and 003A were designed for some serious conditions. One feature is that if the AC regulator fails, the generator continues to put out power. If lightly loaded, the voltage may be high, but communications systems and many other electrical devices can tolerate the 10%-20% overvoltage well. For backup service in civilian use, converting to a more common system like the SX460 regulator and clones provide can make sense, but I wouldn't automatically say this is more modern or an upgrade, just a different system of regulation.

 

[herbertv2]

the AC regulator board was just fine it was the cvt1 that failed parts that are harder to find and expensive to replace, but for a genest that is almost 30 years old no complaints, just meant by bringing it into the 21st was giving it digital gauges, and ridding it of its old style canister filters. Did what i had to do to get it back into service as easily and effectively as possible. not to mention cost effective lol, you can gets roughly 20 or so Chinese 460sx avr, for the price of a NOS CVT1.

Though from my understand one of the reasons these old genset were phasewd out was them not meeting the teir3 emissions standards

edit though will say it was still making power when it was shut down despite cvt1 smoking.