MEP-016E Wiring

[flatdog555]

I just acquired an MEP-016E with only 8.3 hours since a complete rebuild. Everything in this one is pretty much as clean as when it shipped from Ft. Hood TX.
Runs like a champ, but no output on the 120 volt plug on front. I used the voltmeter switch on the front to look at the voltages. 1-0 is about 100v, 2-0 is about 100v, 3-0 is zero volts.
I started tracing out the wiring from the panel mounted schematic as well as a downloaded schematic MEP-016b versions from the web.

Here's the problem I found:
All of the schematics I found show that the generator windings should be:
T1-T4
T2-T5
T3-T6

What I measured (with the windings disconnected from the terminal strip):

T1-T5 0.6 Ohm
T2-T6 0.6 Ohm
T3-T4 0.6 Ohm

All wiring looks new, and there are no shorts to ground in any of the windings.
I can't imagine that they would have changed the winding connections for the "E" version.

I'm wondering if the generator windings are simply labeled wrong? Either by receiving a new generator with them wrong, getting distracted, or maybe seeing how good the new guy is at troubleshooting?

Thanks guys, this is my first post, and I promise I'll follow up with what I find. It's better to share the knowledge than to simply drop out of sight after it's solved.

Flatdog555

 

[jas67]

It sounds like the reconnect switch is set to 120/240 single phase.
If you're trying to get voltage out of all three phases, set it to 208 3 phase.

The reconnect switch is inside the control panel (the front of the control panel hinges down).

The convenience outlet should be hardwired to L1 through a panel fuse.

 

[flatdog555]

Thanks,
I probably should explain it better. I've tried the internal switch in many positions, but the voltages coming out are weird. I know the purpose of the internal switch is to connect the stator windings in different combinations so that I can get single or 3 phase 120 or 240 (or 208 depending on which switch contacts are connected in series or parallel. That part I've got down OK.

When I try to find out why some of the switch positions produce power (but not the right voltage), I keep coming up with it's not connecting the stator windings correctly. Troubleshooting inside the generator a bit more, I disconnected the stator windings and ohmed them out expecting to see an open winding. What I found is that the windings on the stator don't match any other stator on the planet (including a Russian 3-phase generator schematic I stumbled accross). On every other generator head, Terminal 1 connects to Terminal 4, 2 to 5, and 3 to 6. That's what all the schematics I have for the B versions and other military generators show (including the schematic under the cover). Mine is labeled so that Terminal T1 connects to T5, T2 to T6 and T3 to T4.

Another way to say it, here's the differences in the stator windings:
Schematic..........Mine
T1 to T3............ T1 to T5
T2 to T4............ T2 to T6
T3 to T6............ T3 to T4

The stator windings coming out of the generator head appear to be labeled wrong. i think the reason the generator is not putting out the right voltages is that it's connecting the stator windings up all wrong. It just came out of depot repair, and I'm wondering when they tore it apart and put it back together if someone might have mislabeled the stator winding wires, but didn't catch it in a final test (maybe why it came up for auction?)

i would like to correct it, but wanted to see if anyone else ever ran across this before i make a mistake and turn a voltage regulator into a hard to replace lump of coal?
Anyone ever seen wrong wiring come out of a rebuild depot?
Thanks,
flatdog555

 

[timntrucks]

on my 16d there is a switch under the top cover.. 4 flat head screws and it comes off.. that switch must be in the correct postion to get the 110vs.. also check the 2 fuses on the front. 15 Amp

 

[derf]

If you're getting 0.6 Ohms between those wires then they probably mislabeled the wires.

Double check between each wire and the gen case.
You should get nothing (infinity).

Next, check the field stator windings, gen head wires F1 and F2. Book says should be something like 27 Ohms. I got something like 60 Ohms, but I think mine is OK.
What is yours?

Disclaimer: You could destroy your gen or hurt yourself if you don't understand what you are doing and/or if you are careless. I do not recommend that you do the following:
Below is what I would do. I am not telling you to do this.
I would terminate the 6 gen output wires to the terminal strip like this:
T=gen wire, TB=terminal board
T1-TB1, T2-TB2, T3-TB3, T4-TB5, T5-TB6, T6-TB4
I.e. connect it like you would if the wires were mislabeled.

I would mark (so I could reconnect) and disconnect the 2 field wires from the terminal board.
I would mark (so I could reconnect) and disconnect the other (right) side of gen head output wires TBs 1 thru 6.
I would start the gen. I would apply 12V DC to the field wires of the gen. I would measure T1-T5, T2-T6, and T3-T4. I should get somewhere around 40-80V AC on each. They should be similar. If they are then I would reconnect the wires and carefully try it out.
If I didn't get AC output then I would suspect something wrong with the field windings, diodes, or rotor windings.

Or I could roll the dice and just hook up the output wires as if they were mislabeled and cross my fingers.

Remember, the magic blue smoke makes generators work. Once the magic blue smoke is released the generator is broken and will need repair.

 

[flatdog555]

Thanks derf,
That's pretty close to what I was thinking. I had planned tomorrow to connect all 6 wires to a spare terminal bus that I have, and isolate them from the rest of the unit. I was going to hook something small to the field coil, then lock the pressure dump valve on the motor open so I can pull it through. I was going to hook up an oscilloscope to the output terminals and see what the proper phase is for them. If I had a warehouse of parts behind me, I might be tempted to fire it up and see what happens, but I've only got one of everything, and I already have a barn full of lost dreams and hopeless causes. I'm going to take more care on this one.
Thanks for the input. I just found the field wires on terminals 20 and 21 on the voltage regulator, and will probably use an adjustable supply then start looking at the outputs tomorrow.
I found that under the T4, T5, and T6 peel and stick labels that were put on top the same markings stamped into the wire underneath. Not the case on the T1, T2 and T3, they look like they were shortened to put on new connectors and the stamped markings are no longer there. My guess is the T4, T5, and T6 are right, and they goofed up the other 3 when they put new connectors on them. Easy to do, I've made similar mistakes. I have a high amount of respect for the folks that work on these things. Other than the no output, everything else is perfect inside and out, and a really nice job on dressing the cables. Looks like the inside of an old Tektronix instrument, everything laid out like you were going to take a picture of it.
Flatdog555

 

[flatdog555]

26.3 ohms on the field. No shorts between any of the windings and ground.
Will try a spin test tomorrow.
Thanks again,
flatdog555

 

[derf]

Sounds like you have a decent knowledge of what you're doing.
You could tie down the decompression release, and maybe disconnect the fuel solenoid and use the starter to turn it over while you test.

If all is good and you get the wiring sorted then on to the VR.

 

[flatdog555]

Thanks derf,
I took your advice on wiring down the compression release and used the starter to bump the engine while I drove the field with a little power supply. I could have used a lantern battery if I had one, but it worked well to hook up the field wires to about 6 volts and look at the outputs.
I grounded T4, T5, and T6 together and looked at what was labeled as T1, T2, and T3. All were putting out voltage, and looked like the phases were not correct for the direction of rotation.
I used the ohm meter again to verify that T1, T2 and T3 were mislabeled, and put my own labels over the top. I connected it all back up and set the switch for 3 phase output. Now I'm getting voltages like I would expect, but low (90 volts).
I set my meter on HZ and saw it's running at 45. On the MEP-016E version, apparently the motor speed adjust knob is no longer part of the assembly. Instead, they put two heavy springs on the governor and use a giant set screw which was wired into place so it won't turn. I put a little pressure on the governor and saw the HZ climb to 60 on my meter, and on the front panel meter. So that part is working too!
Still no output from the courtesy plug. First problem was the the fuse holder was damaged so that the fuse wouldn't engage both contacts. I replaced it with the spare and now power to the plug, but still no output from the plug.
From the pictures on the web, apparently F1 and F2 used to be used on two outputs of a standard household outlet. When GFI plugs came out, the decided to replace it with one of those. Mine has a stanless steel outdoor cover and a square GFI plug like we have in our bathroom. I ohmed out the plug and found that the GFI had tripped but couldn't be reset. I pulled and replaced it and found water inside. The new plug works fine, and I have a working courtesy light outlet.
I decided to check the oil which I found to be low (why don't I check those things first?).
Anyway, long story short, here's what I found wrong:

1) T1, T2, and T3 stator windings mislabeled
2) Faulty fuse holder in the F1 position
3) Defective/damaged GFI socket
4) Governor adjustment screw set to about 2800 RPM
5) Low oil (didn't change the voltage, but will keep those teeny-tiny parts slipping around better and longer)

With everything corrected, it appears to work OK at this point. I will check each of the switch positions to verify that I don't have a phase reversed, but I think I'm over the hump.
I wanted to document what I found in the hopes of helping others who may stumble across this thread. Thanks to all who helped!
flatdog555

 

[derf]

Good.

Mine had three fuse holder and only one was wired.

With the gov screw that low I'll bet they never ran that motor after it was installed.