MEP-806a No Frequency No Voltage

[metalchips]

Hello all, I've lurked in the past but this is my first post.

I have a MEP-806a that I use to power my machine shop. I have had it since 2013 and put 12,000 hours on it. I've done every repair imaginable to this machine but I currently have a problem I have not been able to solve.

Currently I have no frequency and no voltage. The engine runs great, but I can't get anything from the genset. I have about 40 hours into troubleshooting this and I basically gave up, which is not my style. Here's how to failure / my troubleshooting went:

The first thing to fail was upon start the machine would over-rev and shut down with an over-voltage light when I released the start switch. If I kept it in field flash / starting mode the engine ran properly. I remembered seeing the Hz read out OK during this time but I don't remember the voltage. I suspected a bad governor solenoid so I replaced with a spare and no change.

Next I followed the instructions in the TM to disable the voltage regulator. My thought process was stop the over voltage condition so that I could troubleshoot. With the voltage regulator disconnected the engine stopped over-revving and would run at 60Hz with no voltage. I talked to the eBay seller who sells the voltage regulator kits and he wanted me to seriously check connections so I took 2 days and I did exactly that.

One of the terminals on the re connectable terminal board, I think #7, was loose. This terminal connects a single phase to the control transformer for the voltage regulator, so I thought that could be it. No luck. I found a couple not-so-tight connections on the terminal strips on the bottom of the control box. No luck. Next I removed the control transformer, the droop transformer, and the current transformer and inspected and tested each one. Everything tested OK. I tested the potentiometer for the voltage and frequency. They are good.

At some point during all of this the engine stopped over-revving and the machine stopped making frequency and voltage completely. So, the problem moving forward is: engine runs fine, no frequency, and no voltage.

The next thing I did was continue looking for loose wires. I found a few but looking at the wiring diagrams there's no way these wires had anything to do with the problem. I continued to test the voltage regulator following the TM and I thought it could be bad so I went ahead and bought one. When it came in I replaced it and nothing changed. I got deeper into the TM and the wiring diagram and I chased every wire that has anything to do with the field flash function and the voltage regulator. The diodes in the control box are all good. The resistors in the control box are all good. All of the relays on the back panel are good. The over/under voltage relay is working. 24v from the alternator is perfect. When I hold the start switch down 24v is sent to the exciter every time.

Next I needed to test the genset itself, so I pulled all the leads and removed the end of the genset. I removed the ring of diodes from the exciter and tested them. 2 of the diodes were bad. I replaced them. I did all the tests I could to the genset and everything seemed OK. I don't have a load bank, so I couldn't run any tests that required one. I replaced the bearing that holds the rotor shaft and put it all back together. No change!

Next I re-tested the voltage regulator, the governor, the voltmeter, the frequency meter, the over/under voltage light, the starting switch, the starting relay, the diodes and the resistors. I removed the magnetic pickup sensor and cleaned and tested it. I have it calibrated to pulse 3 volts.

Right now:

Engine runs great
Frequency dial WORKS and adjusts engine RPM
Frequency meter shows nothing
Voltmeter shows nothing
Voltage dial does nothing
Undervoltage light

Does anyone have any ideas?

Since I use this to power my machine shop I rented a generator. I put at least 40 hours into troubleshooting this but I had to stop and get back to normal workflow. The rental generator costs $2000/month so I need to figure out whats going on with this soon. I think that my genset is dead. Unfortunately I can't find any on eBay right now.

Thanks for any advice,

Evan

 

[metalchips]

Some background on my machine:

I bought in 2013 with 1000 hours on the clock. No initial problems. I had to replace the alternator in 2014. The water temp gauge stopped working. I replaced that with an industrial 24v VDO gauge. Normal fluid and filter stuff.

In December 2015 the machine literally melted down. We lost a couple cylinders and it obviously wouldn't run. After removing the enclosure and the engine itself we found that the o-rings that seal the water jacket around the cylinder sleeve were completely rotten. The seals on one cylinder blew out causing coolant to fill the crankcase and the engine to overheat. Turns out the water temperature switch was bad. The engine kept running until it melted a piston. We did a complete rebuild of the engine and it has run flawlessly ever since.

At some point we had an issue with the governor solenoid jamming the engine full blast. Turns out there was a nick in the wire going to the solenoid and it would touch to ground from time to time.

At some point the machine was having trouble keeping frequency when we had heavy motor loads on it. I replaced the governor solenoid for good measure, but the real culprit was the linkage between the solenoid and the injection pump. The ball ends had worn out so much that there was significant play in the linkage. A dead spot if you will. I replace the linkage with new ball ends and I have never has a problem with frequency control since.

In 2016 The machine melted down again, but in a different way. Luckily I was outside and saw it smoking and was able to shut it down. The bearing that holds the genset rotor failed and heated up into a ball of molten metal so hot that it caught the enclosure paint on fire. It was still see-though by the time I removed the enclosure. Once it cooled the rotor was permanently welded to the housing of the genset. Luckily I was able to find a used genset on eBay for $500 and I replaced it without having to remove the entire enclosure. It was a load of work but it was worth it.

So, that means the genset I have is not the original. I don't remember how many hours it was supposed to have on it, but I think it was around 1000. I think I put 2500hours/year on mine so summer 2016 to summer 2018 = likely 6000 hours on that genset.

We have been chasing a coolant leak and an oil leak for the past 2 years. The coolant leak turned out to be a couple pin holes in the radiator where the fan blows against it which were so incredibly difficult to find. All of the online DOD suppliers were quoting me $1000-$1500 for a radiator so I waited until it got bad. When that happened I was able to get one for $600 and I put it in. While I was in there I degreased the combo oil leak / coolant leak disaster. I found a source for the soundproofing and replaced the piece on the other side of the radiator. The oil leak turned out to be the filler neck. The plastic melted/warped and left a big gap where the flange is supposed to seal against the engine. I bought a new one from a John Deere supplier and it did the same thing within 2 months. OIL EVERYWHERE is so annoying. I ended up making a filler neck tube out of steel and I haven't had an issue since.

Oh, and I recently figured out that the exciter brushes in my alternator can be replaced - a $5/15 minute fix instead of sourcing and replacing the alternator.

If anyone ever needs any advice on any of the stuff I have done, part #s, or parts suppliers feel free to contact me. PM or evan@42draftdesigns.com If this is a medical emergency call 911 because I will probably take a couple days to get back to you. I also have hundreds of pictures of the guts of the MEP-806a if anyone is interested

 

[Guyfang]

Did this gen set have the quad circuit mod? When you mesure at the S1, do you have the 24 volts that should excite the main gen?

 

[metalchips]

Hi thanks for responding. I am getting 24vdc on the S1 wire when I flash it. I'm not familiar with the quad circuit mod. I will search.

 

[metalchips]

OK, I found the technical bulletin on here that describes the Quad Circuit modification. On my 60kw machine the TRC voltage regulator isn't labeled "Quad" but the idea is the same. My machine had a fuse inline on terminal 1 when I bought it. I've never had a problem with that fuse.

5.3.1 Issue: The voltage regulation system for the MEP-804A, MEP-805A, and MEP-806A Tactical Quiet
Generators can fail in a mode that heavily damages the main alternator windings, causing the generator
set to be Non-Mission Capable until the alternator and other components are replaced. This
modification adds a fuse into the excitation circuit to protect the main alternator from damage.

 

[Guyfang]

This sounds very much like you have a main gen problem. If you have voltage on pin 7 of the S1, and the wire down to the exciter is good, then that only leaves the main gen.

You replaced the diodes in the main gen, but there could be more damage, you haven't found. I think you need to get into the excitor circuits, and see if you can find out why your not getting the main gen to light off.

 

[metalchips]

I just wanted to check in with you guys. I ended up buying a MEP-805b with 12 hours on it because I couldn't wait. I did a few more tests and again I have voltage going to the exciter field but nothing happens. I really need to remove the end cover of the genset, get back in there and try to determine if it's really dead. I had to move on to another major problem in my shop so I haven't been able to get back to this. Soon, I hope. Meanwhile the 805b is incredible and is handling the demand of my machine shop with the exception of one very large machine that uses regenerative braking. We were set stacking the 806a daily so ideally once I get the 806a back up and running we will use it on demand.

I posted in the classifieds, but if anyone has any leads on a 806a genset please contact me.

Evan
evan@42draftdesigns.com