MEP-006A Voltage Regulator Failure / Questions

[cbrTodd]

I am working with the same MEP-006A generator at the local Christian camp, that I have tinkered with for many years now. For the last year and a half, it has done great, has been used regularly, and has been load banked by a local company for testing / clean out. It has behaved well and got a clean bill of health from the load bank test...

...Until it had an electrical issue during a recent outage and spiked some kind of voltage surge through the camp. It melted a couple breakers and fried several circuit boards in air conditioners, fried the juice machine transformer, etc. They had the company that did the load bank come out and check it and they said the voltage regulator had failed. I don't know who took what apart, but when I saw it the top case to the exciter was removed. The only damage that I can see is a broken wire on transformer NSN 5950-00-101-2387, item number 29 in figure 55 of TM 9-6115-545-24p. One tab was pulled out from the core and the tiny winding was broken. I don't see any signs of damage on the voltage regulator card or any 'toasty' components anywhere in the exciter assembly.

If that failed transformer could cause it to go high voltage (or something else that would have damaged a bunch of downstream equipment), does anyone have a good source to get a new one? They have been calling sources listed from part target and so far the best price they have found is $500 each, minimum order quantity of 2...

One idea I had was if a 400 Hz exciter would have this transformer in it, and could be swapped over to the 60 Hz exciter module they need? Oshkosh has a used 400 hz one in stock that would cost less than just the new transformer, and my look at the parts manual makes me think this is common to both excites, but I was wondering if anyone here could confirm that. They are out of stock of the correct exciter module.

Thanks in advance for any assistance you can provide!

 

[cbrTodd]

The failed lead into the transformer is at the bottom right of the picture, just behind the vertical aluminum extrusion.

 

[Guyfang]

If that is all that's wrong, then yes, the Transformer from the 400 hertz Static Exciter will work in the 60 Hertz machine. But I think you need to be real sure that's all that's wrong.




That's what the UOC, (Usable On Code) is for. It tells you what part fits what model.

 

[cbrTodd]

Thanks Guyfang, I thought that is how the UOC worked, but I wasn't 100% sure. There were specific sections labeled 50/60 hz and one labeled 400 hz too and this was in neither of those, but I wanted to be sure.

Any guidance on how / what to test to confirm that 'only' the transformer broke? I don't have access to the 100 volt variable AC power supply called out in the -34 to test the voltage regulator card (instruction 8-12 of the -34), but that test appears to be directed at the card only and not the rest of the components in the exciter module. The card itself looks fine.

I am tempted to try soldering the lead back on the transformer, verify that voltage is good when the set is run that way, and if so, order a 400 Hz exciter module to rob the transformer from as a more permanent fix.

 

[peapvp]

If I see this correctly, then the transformer in question is T203

T203 is a small 120VAC / 6VAC with 3.6 VA rating and max secondary current of 500 mA AC chassis mount transformer.
This transformer is expensive because it is rated for 50/60 Hz and 400Hz

since this is a 60Hz Genset, any transformer with 115V / 6V ratings will work
As example

Hammond Transformer 266F12B

the ratio of the original is 20:1
The Hammond Transformer has a ratio of 19.667:1

this would be more than acceptable
Connect both sides in parallel for 115 V in and 6 V out since this is a dual coil transformer on both sides
the output current is 600 mA which is also fine

Price: US$ 18.54 plus shipping and tax from Mouser

 

[Guyfang]

The only way to test something is with the right test equipment. Having said that, I would kick out the 16 bucks and give it a try. The picture of the Static Exciter showed me a clean, almost new looking box. The question is, why did T203 get the way it is now? Did the wire break off? Could that have caused the OV (over volt) condition? Why did the OV safety circuit not work right? In the moment that the gen set went OV, the safety circuit should have opened the output contactor. Or did it work right and the mili-second do all the damage? Or, I hate to bring it up, but was the set running in Battle short?

 

[cbrTodd]

The only way to test something is with the right test equipment. Having said that, I would kick out the 16 bucks and give it a try. The picture of the Static Exciter showed me a clean, almost new looking box. The question is, why did T203 get the way it is now? Did the wire break off? Could that have caused the OV (over volt) condition? Why did the OV safety circuit not work right? In the moment that the gen set went OV, the safety circuit should have opened the output contactor. Or did it work right and the mili-second do all the damage? Or, I hate to bring it up, but was the set running in Battle short?

Thank you both for your fantastic input!

I normally hate loading up the parts cannon, but at $20, given the cost of any other action, I think it is warranted here.

The entire exciter module only has about 20 hours on it. I replaced it for them after the previous one failed due to the 'electrician' flubbing the installation and original setup. They had flipped the neutral with one of the hots in the connection box, and to get 120V on their meter in the panel, had turned down engine speed. It was running at about 30 hz and fried something beyond the voltage regulator card in the exciter module. Unfortunately the old exciter module and card appeared to have been discarded at some point by one of the previous maintenance managers at the camp, otherwise I likely would have had a spare transformer there already. It does look like the attachment tab for the transformer lead had pulled out of the wrap and broke the lead loose. There was no sign of it being hot on that tiny transformer wire or the soldered tab that was physically removed from the transformer.

My first thought was that if this transformer is involved in the set sensing the voltage that it regulates to, then it might not have sensed an over voltage condition to set the over voltage fault. I do know that it was running unattended without battle short activated when it failed. The camp manager said it had run for about 6 hours before 'all hades broke loose'.

 

[peapvp]

The only way to test something is with the right test equipment. Having said that, I would kick out the 16 bucks and give it a try. The picture of the Static Exciter showed me a clean, almost new looking box. The question is, why did T203 get the way it is now? Did the wire break off? Could that have caused the OV (over volt) condition? Why did the OV safety circuit not work right? In the moment that the gen set went OV, the safety circuit should have opened the output contactor. Or did it work right and the mili-second do all the damage? Or, I hate to bring it up, but was the set running in Battle short?

The T203 is the power for the feedback circuit for the AVR to express this in simple terms. It receives its primary Voltage from CT4, CT5 and CT6 via TB16 and J13
If this terminal broke while this genset was running with a load, then the AVR would have probably momentarily ( 250 milliseconds ) produced a output Voltage high enough to Trip Fault indicator. CB2 has a app. switching time from ON to OFF off about another 250 milliseconds.
The entire scenario would have taken place within 500 milliseconds

 

[cbrTodd]

It's entirely possible that there is more wrong than just the transformer. That genset has sat in its current location for many years now, with continual intrusion attempts by mice, bugs, skink lizards, etc., with many nests being cleaned out over the years, so anything is possible. I have ordered the Hammond replacement and will report back on what I find once it is installed. Thanks again, everyone!

 

[peapvp]

It's entirely possible that there is more wrong than just the transformer. That genset has sat in its current location for many years now, with continual intrusion attempts by mice, bugs, skink lizards, etc., with many nests being cleaned out over the years, so anything is possible. I have ordered the Hammond replacement and will report back on what I find once it is installed. Thanks again, everyone!

Be careful when testing this Genset.
Make sure all loads are disconnected and verify output voltage on main terminals and convenience receptacle

 

[cbrTodd]

Be careful when testing this Genset.
Make sure all loads are disconnected and verify output voltage on main terminals and convenience receptacle

100% agreed. This unit is connected through a Ronk manual transfer switch that will remain disconnected from the building and anything valuable until after the generator is confirmed to be operating properly again. That testing may be against a home brew dummy resistive load or through another professional load bank test, if the voltage looks ok after the transformer replacement.

 

[Guyfang]

And recheck the ground.