MEP-002 excitation to voltage regulation details

[bimota]

New thread to detail the voltage regulation process from DC excitation to regulation.

Current issue with MEP-002 I am working on to troubleshoot.
1. Upon starting the engine - DC excitation happens and voltage with Start position (so DC voltage is working to start the electromagnetic process) As long as the switch is in Start position the voltage comes up and hz to correct readings
2. The voltage drops after releasing the Start and returning the switch to Run

So looking to find the specific repair for this issue: Yes, I know I can buy a new voltage regulator but I know this can be traced to a specific part on the voltage regulator that can be repaired. Parts are getting harder to find - so detailing specific repair is good to develop.

 

[Ray70]

http://www.steelsoldiers.com/showth...ll-Control-cubicles-interchangeable&highlight=
I had the same problem with one of my -002a's. It would make power as long as you manually flashed the field, as soon as you let go of the start switch the power would die. At first it seemed like a problem with the control cubicle but the real problem ended up being a bad CVT. I got a used CT/CVT from Craig A Tull and once I finished the painful task of swapping it out everything worked perfectly! If you have any way of getting your hands on a known good AC reconnect box, try swapping it out and see if the problem goes away. swapping the CVT is a difficult task that you probably don't want to do as a "test" until you're sure yours is bad. Either that or test the resistance on all the windings to the TM specs. that will tell you if its bad.
Good Luck!

 

[glassk]

Could be the rotating Diodes, they ain't on the board,...

 

[bimota]

The CVT? Interesting - any idea why? I'm speculating that maybe the voltage regulator uses some current flow measurement to stop excitation. Just trying to get the theory and diagnosis down "before cutting and drilling..."

I read about the "linear reactor" and wondered that that was for

 

[bimota]

Could be the rotating Diodes, they ain't on the board,...

Can you explain why? I want to nail it down before surgery, just like I'd want my doctor to do

 

[Isaac-1]

The voltage regulation system on these generators works backwards from the way most generator voltage regulators work, The normal state of operation is feeding full output into the exciter and the AVR circuit board works by lowering this output. Others can give a better description of how all this works, but it involves the AVR board, the CVT as well as a couple of transformers, ... Therefore it is common for the voltage to go high (about 154 vs 120 VAC) when the AVR board fails.

 

[glassk]

Can you explain why? I want to nail it down before surgery, just like I'd want my doctor to do

This is just a guess without testing,

Failure mode: All Diodes Shorted

Effects:
The shorting of all of the diodes in the rotating rectifier assembly will in effect
bias the main revolving field’s DC excitation voltage, and the generator’s terminal
voltage will collapse.


You are flashing the field while holding in start position, giving correct excitation , releasing switch relies on rotating field and voltage drops out,


again just a guess ,...

 

[Keith_J]

No, the rotating diodes are isolated from the field flashing circuit. The problem is either CVT or regulator. Flashing during starting induces current in the rotor through the rotating diodes, then the CVT should take over with the regulator providing fine control of output voltage.

Lima MAC generators only have a type of CVT for voltage regulation, it is a magnetic amplifier control. Neat design, not a single electronic component.

 

[Rapracing]

Here is a thread dealing with the same problem.

http://www.steelsoldiers.com/showthread.php?112824-NO-Voltage-or-HZ-reading-on-meters&highlight=no+voltage