MEP-804A No AC power when start switch is released.

[cdhoov]

I have a MEP-804A that I am trying to fix for my neighbour.
Serial # FZ57811
Unit was used and worked fine and was parked. About 1 year later, attempted to use but it no longer produces AC power.
It will start up and run fine and will produce power as long as you hold S1 in the start position. If you release the power drops off. If you go back in start while running, it will produce power.
After starting and releasing S1, 'under voltage' MIL will come on.
I was able to determine that relay K15 releases when you let S1 go into the run position. It no longer gets its 24vdc + signal. If I apply 24vdc + to 'A' on the K15 coil, the relay will energize and
the generator will produce power. When wire is removed the relay deenergizes and Gen quits producing power.

I know very little about these units other than what I learned with the wire diagram on the unit.
My employment is working on diesel generators. These units are fairly complex and with the limited information I currently have, I feel somewhat limited.

If you can assist me with more technical manuals or things to check, I would appreciate that.

I have seen numerous threads with similar issues, but none that I found really came to a conclusion.

 

[Guyfang]

Please look at the TM forum here in SS. All the TM's needed to work on the set are in the TM forum.

One fast thing. Open the control panel and look at the A2, volt regulator. Right next to it should be a big fat fuse. Well, should be there. Not all sets were updated. But if its there, pull it out and test it.

 

[cdhoov]

The fuse is there and does test good.

Thanks for that. I do now see the TM section and will see if I can locate what I need.
If you come up with any other quick ideas, let me know. Meanwhile I will be looking at the TM....

A couple questions so I better understand the operation.
1) What is the purpose of the 'battle short' switch? It seems that if I turn that on while holding S1 in start, it will cut the power.
2) The contactor Trip section of the MIL panel. Is this referring to the contactor on the output of the gen? Where it will de energize if it sees an issue?

 

[cdhoov]

Is the K15 relay supposed to be energized when the unit is producing power?
My assumption is that it is.
The A side of the coil (K15) gets power from #7 on S1. However as soon as you release S1, #7 will deenergize. So if K15 is supposed to remain pulled, where is it supposed to get the signal?
The only location that I can determine that it could come from is 'P'. P is connected into this circuit, however I have not been able to determine where the rest of the circuit is?
If it is not from the 'P' circuit, where else does it get its signal?

 

[Guyfang]

The fuse is there and does test good.

Thanks for that. I do now see the TM section and will see if I can locate what I need.
If you come up with any other quick ideas, let me know. Meanwhile I will be looking at the TM....

A couple questions so I better understand the operation.
1) What is the purpose of the 'battle short' switch? It seems that if I turn that on while holding S1 in start, it will cut the power.
2) The contactor Trip section of the MIL panel. Is this referring to the contactor on the output of the gen? Where it will de energize if it sees an issue?

The S7, (Battle short) is used to bypass most of the saftey circuits on the gen set in case of an emergincy situation. You can not start the set with S7 in the on position. Nor try and flip up the S7 during the start process. The system is not designed to allow it. I am not sure what you mean by "Contactor Trip Section". Are you refering to the A2, (Malfunction Indicator)?

 

[cdhoov]

The S7, (Battle short) is used to bypass most of the saftey circuits on the gen set in case of an emergincy situation. You can not start the set with S7 in the on position. Nor try and flip up the S7 during the start process. The system is not designed to allow it. I am not sure what you mean by "Contactor Trip Section". Are you refering to the A2, (Malfunction Indicator)?

Yes, I was referring to A2. It has 4 lights (UV, Short circuit, Overload, Reverse Power)
Above the MIL it says 'contactor trip'
Was curious what that means.

 

[Guyfang]

Yes, I was referring to A2. It has 4 lights (UV, Short circuit, Overload, Reverse Power)
Above the MIL it says 'contactor trip'
Was curious what that means.

It means that all of the above red situations, will result in an a kicking out out of K1, when these failures are noticed.

 

[cdhoov]

OK, that makes sense.

Any thoughts on my questions on Post #4?

 

[Guyfang]

Is the K15 relay supposed to be energized when the unit is producing power?
My assumption is that it is.
The A side of the coil (K15) gets power from #7 on S1. However as soon as you release S1, #7 will deenergize. So if K15 is supposed to remain pulled, where is it supposed to get the signal?
The only location that I can determine that it could come from is 'P'. P is connected into this circuit, however I have not been able to determine where the rest of the circuit is?
If it is not from the 'P' circuit, where else does it get its signal?

No, K15 is not supposed to stay energized after letting the S1 go.
The letter P denotes a test point, pin P, on the J3 Diagnostic Receptacle.
The K15 is supposed to give initial excitation. When the S1 is released, the A1 is supposed to take over the excitation process. It, A1, senses 120 volts, (or thereabouts) and then takes over.

Below is the test procedure for the A1.

 

[cdhoov]

This was the results that I got

Termanal 1&2 1.2 vac (checks out OK)
Terminal 3&4 no voltage unless I am in the 'start' position with S1
Terminal 5&6 no voltage regardless
Terminal 7&8 no voltage unless S1 is in the 'start' position. Then have 55vac

I tested the OHM's on the wires that go to 7&8. There is no continuity what so ever when I remove the wires from the regulator and test OHM's on the wire.

The thing that confuses me here is, if we have no continuity on these wires (stator?) how can the gen work when S1 is in the start position?

Having no DC voltage at 5&6 means what? This is the exciter field. Here again, how does it work when S1 is in start position?

 

[Guyfang]

This was the results that I got

Termanal 1&2 1.2 vac (checks out OK)
Terminal 3&4 no voltage unless I am in the 'start' position with S1
Terminal 5&6 no voltage regardless
Terminal 7&8 no voltage unless S1 is in the 'start' position. Then have 55vac

I tested the OHM's on the wires that go to 7&8. There is no continuity what so ever when I remove the wires from the regulator and test OHM's on the wire.

The thing that confuses me here is, if we have no continuity on these wires (stator?) how can the gen work when S1 is in the start position?

Having no DC voltage at 5&6 means what? This is the exciter field. Here again, how does it work when S1 is in start position?

Was the main gen warm or hot when you checked wires 7&8? Did you perform the test IAW the instructions on the page I attached? Read the last few lines?

 

[cdhoov]

The gen was warm. I had been running it off and on for a few minutes prior to the check.
I did perform the test IAW the instructions you sent me.
If I removed wires 7&8 and tested the wires for continuity, it was open circuited.
However, if I manually press relay K15 while testing this, I would get a reading of 28 OHM's

 

[cdhoov]

I'm looking at the attached diagram. This is the diagram that is on the unit.
I'm comparing this with the Quad circuit test sheet you sent me.

Quad circuit sheet Colored schematic
T1&2 voltage adjust - T1= F1 T2= not used
T3&4 120vac sensing- T3=F2 T4= sensing
T5&6 exciter field- T5=volt adj? T6= transformer
T7&8 Quad circuit- T7=xformer T8= ????

So I'm a little confused with the Quad circuit sheet you sent me. Is it correct for this unit?
The Quad circuit sheet references the -24 TM. I have not been able to locate this on the forum. Do you have access to it?

 

[Zed254]

All the TM's you need to work on the MEP-804A

This should be all the TM's you need to work on the MEP-804A generator set.

www.steelsoldiers.com

MEP-804A, MEP-805A and MEP-806A Main generator Diodes.

Here is some very good information for testing the Diodes on the MEP-804A, MEP-805A and the MEP-806A generators set main generator.

www.steelsoldiers.com

Governor Control Unit Information for the MEP-804A, MEP-805A and the MEP-806A

Here is some VERY good information on the Governor Control System for he MEP-804A, MEP-805A and the MEP-806A.

www.steelsoldiers.com

Electric Governing System for the MEP-804A and MEP-804B Generator

The inclosed list shows you the Part Numbers and NSNs for the two Electronic Governing Systems for the MEP-804A and MEP-804B Generators. The systems are made by LIBBY and TRC. The parts can NOT be mixed. Failure to heed this warning can lead to equipment damage according to the TM 9-6115-643-24...

www.steelsoldiers.com

....from a search of the SS TM section: top of page, far right "TM"

 

[cdhoov]

So based off of my testing per TM9-6115-643-24- section 4.1.1. I am thinking I have a bad AVR.
The first 2 tests checked out within spec.
The last test is checking OHM's
The spec's they give are as follows-
Move voltage adjustment potentiometer CCW. @ 50HTZ=0 OHM. @ 60HTZ=3000 OHM.
At full voltage it says it should be 10,000 OHM.

The results I got are not exactly the same but similar. Wasn't sure how precise it needs to be to those numbers till this is potentially an issue.
60 HTZ- Potentiometer CCW=6,000 OHM. CW=12,000 OHM
50 HTZ- Potentiometer CCW=2600 OHM. CW=8800 OHM

I really appreciate the help so far! If somebody can chime in if these numbers are acceptable or can direct me on further testing, that would be greatly appreciated.
If these numbers are acceptable, and you have a suggestion on where to purchase an AVR, please provide.

Thanks

 

[Guyfang]

So based off of my testing per TM9-6115-643-24- section 4.1.1. I am thinking I have a bad AVR.
The first 2 tests checked out within spec.
The last test is checking OHM's
The spec's they give are as follows-
Move voltage adjustment potentiometer CCW. @ 50HTZ=0 OHM. @ 60HTZ=3000 OHM.
At full voltage it says it should be 10,000 OHM.

The results I got are not exactly the same but similar. Wasn't sure how precise it needs to be to those numbers till this is potentially an issue.
60 HTZ- Potentiometer CCW=6,000 OHM. CW=12,000 OHM
50 HTZ- Potentiometer CCW=2600 OHM. CW=8800 OHM

I really appreciate the help so far! If somebody can chime in if these numbers are acceptable or can direct me on further testing, that would be greatly appreciated.
If these numbers are acceptable, and you have a suggestion on where to purchase an AVR, please provide.

Thanks

Those numbers look good enough, or better said, close enough.

 

[cdhoov]

OK,
I really appreciate your help.
Looks like I need to hunt up an AVR.

Thanks

 

[Guyfang]

I'm looking at the attached diagram. This is the diagram that is on the unit.
I'm comparing this with the Quad circuit test sheet you sent me.

Quad circuit sheet Colored schematic
T1&2 voltage adjust - T1= F1 T2= not used
T3&4 120vac sensing- T3=F2 T4= sensing
T5&6 exciter field- T5=volt adj? T6= transformer
T7&8 Quad circuit- T7=xformer T8= ????

So I'm a little confused with the Quad circuit sheet you sent me. Is it correct for this unit?
The Quad circuit sheet references the -24 TM. I have not been able to locate this on the forum. Do you have access to it?

That down load was not the same down load I sent you. One of us has made a mistake.

 

[Guyfang]

OK,
I really appreciate your help.
Looks like I need to hunt up an AVR.

Thanks

Now, lets talk A1's. There are two different kinds of A1's. LIBBY and TRC. You can not mix them. If you have a LIBBY, then you need several other parts, too also be LIBBY. The same with TRC.

Click on this link. It tells you how to confirm that you have ALL the needed parts, in your gen set. Unless you have seen this gen set work before, then take a few seconds to look at the parts to be sure they all match. THEN look for the right A1. There was some in the big auction site not long ago.

View attachment Volt Reg-MEP-804A & MEP-804B.pdf

 

[cdhoov]

I never personally saw it work, but my neighbour said that they were using it and it worked fine when they parked it. 1/2 a year later when they went to use it again, it didn't work.

I have the Libby regulator
model #122-3054
PN- 30554SOCN88-22560

I'm trying to determine if I have the correct parts. Having a little trouble with it.
Volt adjust rheostat- Don't see a PN that matches, but based on my testing, appears to be 10k ohms
R16 resistor- Was not able to determine where this is?
Transformer- Is correct