MEP-002A Left Connected when Main Power was Restored

[Guyfang]

Ok so i checked the three wires as best as i could. I was able to find the terminal for X1 and i think X3 on S6. Both of these registered the same ~65 volts that i was getting on the L1 and L3 lugs. X2 was completely unreachable without removing S6 from the control cabinet which i did not want to attempt. Since these wires were connected directly to the J9 connected at theh back of the cabinet i decided to disconnect the J9 plug with the genset running. Once disconnected I checked every pin inside the connector coming from the genset. I got readings of less than 1 volt on all the female pins inside that connector end. Thinking "That's weird because at least two of them should show ~65v..." i plugged it back in and check the X1 and X3 terminals again, and this time i didn't get the ~65 volts on either. So basically I'm getting nothing on any of those wires now and i'm worried that disconnecting the J9 while the genset was running may have damaged something else entirely as i'm getting no line voltage on X1 or X3 like i was just a few minutes ago. So it seems like whatever problems i have are in the genset itself, not in the control box right? If so what did removing J9 while the geset was running do to drop the voltage output of the genset to 0v?

You lost the excitation. That's what. When you started it up, the excitation voltage goes to the main gen. When you removed the C-plug, that removed the initial excitation. I dont think anything else was damaged.

Instead of taking the C-plug off, you should have tried to measure at a TB. Terminal board.

 

[Turbinetester]

I'm wondering if the selector switch being stuck, which from your comments above, was not the case before the power restoration event is a symptom that's being overlooked. If that's the case, I would take off the side panel and just loosen the nuts on the wafer switch and spray contact cleaner (Deoxit, or CRC, etc.) on the wafer/contact sections and work the switch back and forth to free it up and break any oxidation points.

If by chance the switch somehow arced or became pitted the switch may be damaged or worst case toast. However, you did indicate in your posts that you tested the outputs off that switch and the outputs were correct if in fact you read the voltages off the correct output wire terminals.

Regardless, a stuck switch can be problematic in that it could have oxidation on the wafers/contacts and lead to intermittent contact behavior.

I'll begin working on the switch and see what i can accomplish in terms of loosening it up to move again. Is there a video or pictures on another thread anywhere where someone has gone through this before?

 

[Turbinetester]

You might want to check the contacts on the switch to make sure they didn't burn off...

Or maybe the breaker tripped from the reverse feed. Hmmm

I've tested the breaker and it correctly shuts off the power to L1 and L3 when it is moved down. Other than that the only thing i could attempt for that is to try and remove it from teh cabinet and replace it with a brand new breaker. It is really really tight in there and i was not able to get even get the voltage probes on the the terminals of the breaker, much less remove it. I gave up rather quickly though, i may be able to get it out with more persistance.

 

[Turbinetester]

You lost the excitation. That's what. When you started it up, the excitation voltage goes to the main gen. When you removed the C-plug, that removed the initial excitation. I dont think anything else was damaged.

Instead of taking the C-plug off, you should have tried to measure at a TB. Terminal board.

Yes you are correct. When i restarted the gen all was back to (sub) normal performance and i had ~65v at the output lugs. I looked over the wiring diagram and did not see a TB that would have allowed me to get readings on X1A8, X2A8 or X3A8. Where would that terminal board be located? Is there any way to do a functional test of the direct output of the generator itself, short of having a spare control box?

Request: Is there anyone in Georgia, near Macon, that might have a spare control box i could borrow to test?

 

[tobyS]

Unless the breaker has a functional defect, like won't close or open both poles, I would not take it out. I'm an electrician ....but not experienced on this generator, so can't give much help.

 

[Guyfang]

Unless the breaker has a functional defect, like won't close or open both poles, I would not take it out. I'm an electrician ....but not experienced on this generator, so can't give much help.

You can of course test the CB without running the set. CB1 open, no continuity between contacts 3&4, 7&8 and 11&12. CB1 closed, continuity between 3&4, 7&8 and 11&12.

 

[Guyfang]

Yes you are correct. When i restarted the gen all was back to (sub) normal performance and i had ~65v at the output lugs. I looked over the wiring diagram and did not see a TB that would have allowed me to get readings on X1A8, X2A8 or X3A8. Where would that terminal board be located? Is there any way to do a functional test of the direct output of the generator itself, short of having a spare control box?

Request: Is there anyone in Georgia, near Macon, that might have a spare control box i could borrow to test?

Just looked again. No TB. I assumed. Thats always wrong.

You can remove the top of the box. Then remove the TB1, (load terminal board). Then tape up the wires that go to the TB1. Then your access to the S8 is vastly improved.

 

[Turbinetester]

You can of course test the CB without running the set. CB1 open, no continuity between contacts 3&4, 7&8 and 11&12. CB1 closed, continuity between 3&4, 7&8 and 11&12.

I had a relay one time, 12v, that would show continuity across the load terminals with contactor voltage applied, and show open with no contact voltage. I spents days tracing problems in that circuit until i came back to the Relay and just swapped in a different relay to test the rest of the circuit. Lo and behond the new relay fixed the problem. The root cause ended up being that the relay contacts would touch just enough to pass continuity, but not enough to pass sufficient current for the circuit to energize. That was an eye opening experience to say the least. I'm not sure if the same potential problems could occur in 120v circuit breakers, but i imagine that they could.

Is there wa way to test the raw output of the generator itself to help narrow down the problem? Is it possibel the rotating diodes would pass the directional continuity test and still be damaged?

 

[Guyfang]

I had a relay one time, 12v, that would show continuity across the load terminals with contactor voltage applied, and show open with no contact voltage. I spents days tracing problems in that circuit until i came back to the Relay and just swapped in a different relay to test the rest of the circuit. Lo and behond the new relay fixed the problem. The root cause ended up being that the relay contacts would touch just enough to pass continuity, but not enough to pass sufficient current for the circuit to energize. That was an eye opening experience to say the least. I'm not sure if the same potential problems could occur in 120v circuit breakers, but i imagine that they could.

Is there wa way to test the raw output of the generator itself to help narrow down the problem? Is it possibel the rotating diodes would pass the directional continuity test and still be damaged?

Diodes work, or not. I have never seen anything in between.

Have seen the same kind of fault you described, in wiring, switches and relays also. Once I had a gen set C-Plug with a pin pushed back far enough to read ohms, AND voltage. But would not pass current. I was on the verge of filling my pockets with rocks and jumping into the Main River. Like you, last gasp, changed the whole Special Relay Box, and it worked. Four hours of tearing the wire harness and C-Plugs apart. Ohms are to be taken with a grain of salt. In German, an Ohms tester is call a "Lugensager", Teller of Lies.

I'm not sure if the same potential problems could occur in 120v circuit breakers, but i imagine that they could.
I often saw this in output relays in the DOD gen sets. Normally I measured before the CB or Switch, and after, to see if I had the same voltage. Very common failure.

 

[Triple Jim]

In German, an Ohms tester is call a "Lugensager", Teller of Lies.

Now that's funny!

 

[Turbinetester]

I'm wondering if the selector switch being stuck, which from your comments above, was not the case before the power restoration event is a symptom that's being overlooked. If that's the case, I would take off the side panel and just loosen the nuts on the wafer switch and spray contact cleaner (Deoxit, or CRC, etc.) on the wafer/contact sections and work the switch back and forth to free it up and break any oxidation points.

If by chance the switch somehow arced or became pitted the switch may be damaged or worst case toast. However, you did indicate in your posts that you tested the outputs off that switch and the outputs were correct if in fact you read the voltages off the correct output wire terminals.

Regardless, a stuck switch can be problematic in that it could have oxidation on the wafers/contacts and lead to intermittent contact behavior.

OK i've got some contact cleaner and i've removed the TB1 load board so i have good access to the switch now. I see two nuts facing the front of the output box, on the left and right side of the wafer switch. These are the only two i can loosen up without remove nuts or bolts that hold the entire switch assembly in place. Will loosenign these two nuts allow me to separate the wafers enough to get cleaner down in there?

 

[Chainbreaker]

Yes, there should be two screws that run the full length of the switch that you want to just loosen, not remove. If your switch is stuck that should allow just enough slack to free the switch and allow you to spray contact cleaner throughout the length of the switch so it makes its way into the contact area of the switch internals. Then work the switch back and forth multiple times & respraying contact cleaner into the full length of the switch area.

Then retighten the two nuts that you loosened and see if you can continue to turn the switch handle. It should require firm pressure to rotate the switch knob but it should move freely now to all switch positions. Hopefully that will eliminate any intermittent switch contact operation you might have been experiencing.

 

[Turbinetester]

Thank you to everyone who has stuck with me thus far.

BLUF: I have 240v power again!!!

My switch was mounted to the control box by four screws coming into the interior of the control box from the front of the generator unit, and what appeared to be two screws that entered from the rear of the unit, with screw heads located in the gap between the diesel fuel tank and the control box. The only other "screws" that appeared to be part of the switch were the zinc yellow dichromate roads that ran the length from the rear of the switch towards the front, terminating in a short threaded portion secured with small nuts and lockwashers. I was only able to loosen the nut closest to the cover panel access door, until I removed the 6-8 screws holding the circuit breaker to the front of the control box. Once I was able to move the circuit breaker out of the way I could get a box wrench on the inner nut. It appeared to be that the only way to get the wafers to potentially separate was to remove the four bolts mounting the switch assembly to the front of the panel AND the two bolts attaching the switch assembly to the rear of the panel. The two vertical faces of the interior of the control box seemed to tightly sandwich the wafer together. I did not want to try and remove that switch unless I really needed to do so. Loosening the two nuts did allow the switch itself to be rotated, but none of the "wafers" would separate. I sprayed contact cleaner everywhere I could attempt to get it to land on that switch anyway. I was finally able to get the switch to rotate, but only clockwise at first, and it would, with a fair amount of force, do a complete circle clockwise. It refused to turn counter clockwise until I had completed about 10 full turns. During the process of turning, it seemed to never "land" in one of the correct orientations on the indicator on the front panel (at N, E and W) rather it always seemed to be somewhere in between at some odd angle. When it finally loosened up enough to turn counter clockwise it had the same behavior. Once I tightened the two nuts back up, the switch was again stuck wherever I left it and would not turn CW or CCW. So I loosened the nuts and turned it several times until I could get it to "land" at the 1 Phase 240V setting (pointing E) and be correctly oriented. I will note that this was the same position it was stuck in before I loosened the switch nuts. After doing that, I tested continuity at the breaker since I had such easy access to it. None passed continuity with the breaker off, but at first only one pole was showing continuity with the breaker ON. After spraying contact cleaner into all the nooks and crannies on the top, and cycling it maybe 6-10 times, I was able to get continuity across the two outside legs of the breaker in the ON position. As I don't anticipate needing 3ph power anytime, this was good enough for a test. First I taped up all the exposed wires I had disconnected from the breaker, and secured them where they weren't a danger, but so I could still get a test probe on the terminals somewhere. Then I started the unit and was able to test the wires at the terminals before the breaker and I then got 120V on each of the two legs. I shut the set off, tested the terminal to make sure nothing was live (just to be sure) and then wired up the breaker and the L0-L3 lugs again. Fired it up and again got 120v on each leg. I've now got it all closed back up with all the panels and covers back in place and i'm getting 240v across lugs L1 and L3 so I’ve power again! I don't know if cleaning the contacts on the circuit breaker or fiddling with the switch fixed the issue but I never plan on moving that switch again. I am concerned that the breaker won't pass power on the middle leg. Is there an easy replacement for that breaker switch?

I’ll likely start a new thread to document and seek help on reconditioning on the unit to as like new as i care to make it. There are several items I know need some attention:
Voltmeter seems to be dead, unsure of Ammeter at this time, Frequency responds to RPM
Middle Pole of Breaker doesn’t make contact
Fuel tank is disgusting
Fuel level meter is dubious
Need to get the unit elevated and either mounted to something permanent or put onto a trailer.
Wow this joker is loud, really need to build or acquire some type of sound dampening enclosure.
The 2x12v Starting batteries will drain steadily, so i keep them disconnected until i want to start the machine. I either need to install a 12v switch, or determine why there is a power drain with nothing on.
Probably need to replace fuel and oil filters and change the oil.
Probably should do some preventative maintenance on the genset itself. Some kind of preserving oil or something sprayed onto the windings to prevent corrosion?

Thanks again to each of you that helped along the way.

 

[Guyfang]

If you look in the -24P TM, you will notice that there are 2 switches. Old style, and new style. Try the part and NSN numbers in flebay. I seem to remember seeing one a while back.

As for the rest of your list, please start another thread. Will give you more visibility if you do.