mep002 voltage up and down

[gavland]

ok kinda new at this, i got a mep002 and was missing some diods on the a2 board/voltage regulater. voltage stuck at 90 volts. i also had a parts mep002 i got with it so i swithed the board.
now the voltage keeps going from 90 to 140 +- when i plug anything into it voltage drops to almost nothing till i shut it off and restart it. is the board i put in bad too or is one of the other parts in there bad also PLEASE HELP i dont undersand electric that much but can fix engines so iam not that dumb lol thanks for any help

 

[jamawieb]

Please download the TM's for the generator, that will help you troubleshoot everything. It's more than likely a diode on the board or the transformer.

 

[gavland]

thanks gave it to a friend that knows about generators and electric way more than i do. think ill stick to working on trucks and engines more lol

 

[gavland]

so update on my broken down mep-002
so my friend/generator guy, put a good/used rheostat and (A2) regulator that he got from one of you nice people and still the same problem

if any one has any idea at all please HELP
and or any place in PA near north of philly that knows what there doing with these. i will drive couple hrs if thats what its going to take to get it fixed since my guy has no idea. (works on cummings propain/natrual gass ones) and i dont know about electric just engines.

 

[Isaac-1]

Have you tried going step by step through the troubleshooting section of the TM? Also can you tell us a bit more about what it is doing, is it stable at start up then swinging, or does it start up steady then get worse. Also is this voltage swinging back and forth or does it tend to jump and stay high or low?

Ike

p.s. also since it had work partly done on it when you picked it up, you may need to confirm everything in the voltage regulation system is installed right. I bought a MEP-003a last year that had a high voltage output problem, after a couple of weekends of fighting it I traced the problem to a T-2 transformer that was installed backwards/upside down

 

[Keith_J]

Sounds like the diodes in the rotor are shot. See the -34 TM as to their replacement. Had one like this when I was active duty. Real booger to diagnose with the -20 and direct support didn't want to look through it until I had gone through all throubleshooting, including replacing all filters

Basically, these are brushless generators. The rotating magnetic field (remember, electricity is made by moving a magnet through a coil) is induced through a secondary set of windings. The induced current is AC, diodes change it to DC. This rotating magnetic field varies in strength proportional to the load on the generator, this is the purpose of the regulator. So when greater field current is called for, weak diodes can fail either open or closed. When open, no current. When closed, current alternates so magnetic field alternates and the regulator goes haywire.

The diodes in question are accessed by removing the back plate off the generator. I don't know if it is delta or wye wound so check the TM for testing these diodes with a multimeter.

 

[Isaac-1]

To follow up on that last message by Keith, you may want to ask your generator service friend if he tested the rotating rectifier diodes?