How NOT To Replace The Voltage Regulator In Your MEP-701a

[Beerslayer]

Yep. This is the tale of an Epic Fail.

As it is hard to caption photos on this forum, I will break up the posts a bit.

First, the end result.

 

[Beerslayer]

So I bought a generator trailer at auction, one of the gennys worked fine, the other one didn't make any power. The military spec replacement VRs are a little tough to get and expensive. I have seen many mentions here and on Smokestak of using a Stamford Newage SX460 clone with good results. They look like this, at least before the magic smoke gets out.

Isn't it pretty, all bolted in there nice and tight?

 

[sewerzuk]

That looks like a little bit 'o transistor....
Was this the damage that had already occurred before I spoke to you, or was MORE magic smoke exorcised from that little thing after our conversation?

 

[Beerslayer]

I think the damage was already done. When I hooked it up again with a certain 120vac input and fired it up. there was flames and smoke out of that transistor. The picture above is after I spoke to you.

 

[Beerslayer]

Originally I thought it would be less trouble to just have a generator shop fix it. So I went and talked to them. All of them in Oregon. One shop was really nice, Battin Power. They did say that the only way they could guarantee an outcome was if they replaced all the generator controls with theirs. On a big generator it would make sense, but on a little one, I might as well just buy a new one.

The only shop that would agree to repair the existing controls was in Roseburg. So I took it down there. Well then he couldn't find a regulator for it. Turns out he buys all his parts from Battin Power and was going to call them for help. So I shipped him one. Months later, all he had done was diagnose a failed VR, which I already knew, and made some marks on the wiring diagram that came with the VR, as below.

Edit: Those pen marks on that diagram cost me $75. They wanted twice that but agreed to cut the bill since they didn't really do anything.

 

[Beerslayer]

So I brought the generator home and proceeded to scour the internet for clues on how to fix or replace the VR. In retrospect I would have been better off to just buy a new replacement military spec VR. This project would have been long ago done.

I learned something very interesting while researching this project over the last eight months. There are two kinds of help available on the internet for this specific issue.

Type 1: I asked for help here on Steel Soldiers and got...

"Electricity is dangerous!!! If you don't already know how to do this you shouldn't attempt it!"

So for that ^^ guy, you know who you are, you already had your say, please don't crap in this thread. I am a journeyman wireman, have over 25 years experience working with live voltage up to 12,500v, and don't need my safety hand held. All I asked for was if anyone knew any good text books on generator theory.

Type 2: Here on Steel Soldiers and on Smokestak...

Some very nice and knowledgeable people made helpful comments that sent me in the right direction. BUT, I realized that most of the people with any experience fixing these things were buying generators, fixing them up and reselling them. They, 'you', my gentle readers, are also the same fellows bidding against me in those GL auctions.

So with the exception of Sewerzuk, who came in here just lately with his generator threads, there wasn't any specific help that even a nerd and electrician like myself could follow. I know, I read ~every thread.

I do understand. Well so far, this generator has kicked my rear, but I am going to figure it out. And when I do, I am going to publish a Very Detailed thread, something on the order of what the True Gentleman and Scholar Sewerzuk has done, on Exactly How To Retrofit a Commercially Available Voltage Regulator On An MEP-701a.

So the instructions that came with the Chinese made Stamford Newage clone VR were grossly inadequate. That is what contributed to the release of the magic smoke.

 

[Beerslayer]

I read the entire TM for the MEP-701a. It was like reality TV. Based on the actual generator, but partly fiction. All the same, you do need to read it.

TM 5-6115-615-12

The wiring diagrams, somewhat useful, but partially fictional, are on pages

4-64 and 4-94

You have to use both of those pages together in order to make sense of how things are connected. The idea is that you are supposed to go to military tech school, get certified on these generators, then when they break, blow them up with C4 or surplus them out on GL. And order new ones.

So here's the drawings with my markups.

 

[mikev]

Great story board and I liked how you broke it into individual posts...

Good luck on the VR journey as I have looked high and low for reasonably priced surplus USGI VRs and they don't seem to be available no matter the price - especially the "matched set" (VR and gauge)...

I'll be waiting for your next "installment"...

 

[Beerslayer]

Newage Stamford does publish a really good manual on THEIR voltage regulator that the Chinese knockoff. The knockoffs are pretty faithful to the original design. Here is the manual that has the information you need.

Just for clarity, I have uploaded both the good wiring diagram and the crappy one. Notice the difference? You would think if they were going to copy the VR, it wouldn't be that hard to supply a good connection diagram as well. Nope. Too hard.

 

[Beerslayer]

One of the things I did wrong was I didn't install a jumper between terminals 3 and 4. It wasn't stated anywhere in the manual that came with the VR what that jumper was for. But if you look at the genuine manual, it states that the jumper must be installed if the voltage across L1 & L2 is 120vac. Which mine was. The images below contain some helpful information. If you really think about it. And go to Generator School.

 

[Beerslayer]

Here is where things really start to go wrong. In the photo below of the installed VR, notice that there is no jumper across pins 3 & 4.

But that's not all that's missing....

-or

But Wait! There's more!!!

 

[kurtkds]

Beerslayer I feel your pain. LOL I picked up a MEP113a out of JBLM last summer, was the high bidder when I realized that I had won a 400HZ boat anchor.

Anyhow, Got it home got all the missing filters replaced, fresh fluids back in it, crossed my fingers and hit the start switch. The engine fired up and ran smooth but no power, long story short, replaced the head with a Marathon head and VR. Had the unit back up and running for the Snow/ Ice storm.

http://www.steelsoldiers.com/auxillary-equipment/56948-400hz-gen-sets-able-do-60hz-7.html

I am running my AC side totally separate of the original wiring for now. I've been pouring over the wiring diagrams trying to figure out how to tie the non military VR into the system but so far I get dizzy. lol

Anyhow, the Marathon VR is a SE350 not sure if that would be an option.

 

[Beerslayer]

Notice that I have helpfully labeled the terminals in the photo for VR1 with the correct terminal numbers. The second row of numbers are the corresponding terminal labels for a Newage Stamford VR. Well except for the ones I labeled POT. No, not the Mary Jane kind of POT, but rather the Potentiometer kind of POT. If you go back to the GOOD drawing above, you will see that terminals 1 & 2 can either be jumpered or connected to an external potentiometer or Voltage Trimmer. That is the Voltage Adjuster Thingy or hereafter known as VAT.

There are two things I know for a certainty that I got right here. Terminal 20 & 21 are F1 and F2. That's the wires that go to the Exciter Field Windings. That's one thing. The second thing is that I know I got right is L1. The FM is Very Clear that L1 goes to terminal 27. L2 is another matter. The FM is ambiguous, or WAY over my head at the least, and so the Determination I Have Made, is that What Would Pass For L2 in the Civilian World of Power Generation would be what is terminated on terminal 24.

On a correctly operating generator [on the same trailer] the voltage across T24 and T27 is in my case 107vac, close enough to 120 for me.

And so, now the photo that I have all dolled up for you.

 

[Beerslayer]

This next photo graphically illustrates the Second Thing I Did Wrong. Besides getting out of bed today. If you refer to the photo directly above, you will notice on T24 AKA L2, there are two smaller wires in a red connector and another wire underneath in a blue connector. All three of those wires were landed on the L2 terminal on the SX460 VR. As shown below.

When it came to T27 AKA L1, my lovely wife brought out a Tunafish sandwich made with homemade dill pickles and fresh homemade bread, and I forgot all about the Sneaky Black Wire that you can see landed on T27 on TOP of the other wire hiding behind it. So that black wire you see in the photo above, and clearly NOT landed on L1 in the photo below with its erstwhile mate from the photo above MAY well be part of why the magic smoke escaped from the obviously fake Chinese copy of a Stamford Newage SX460 voltage regulator that was destroyed in my less than capable hands today.

 

[Beerslayer]

So if I may summarize. And I may, since this is a monologue at this point.

1. I failed to install the jumper on the VR between T3 & T4. This is required if your input voltage is 120vac which mine was. Well 107vac, close enough. So for those of you conversant in the TwitterVerse, that was a #fail. For the rest of us, disregard #fail.

2. I failed to terminate the Sneaky Black Wire from T27 on the old VR on T7 on the New Fake Chinese Knockoff of the Venerable Stamford Newage SX460 Voltage Regulator.

Now this is where things get a bit squishy. I would surmise that one or both of my mistakes might have resulted in the epic fail of the Cheap Chinese Knockoff of the Venerable Stamford Newage SX460. Bear in mind that this particular failure resulted in Flames and Smoke reaching towards the heavens. Yes. It caught on fire. And I was too busy shutting down the genny to take pictures. I feel Really Bad for that.

So the squishy part, and where I really need incisive commentary from those here much wiser than myself, is;;;

A. If I had connected things the way I think I should have, would it have worked? Made power somewhere in the 120vac range?

B. What is your opinion? Was it the lack of the jumper, or the lack of termination of the Sneaky Black Wire that caused the Epic Fail?

C. Well I don't know. It has been a long day and I am about done here. Got my butt kicked and went back into the house with my tail between my legs. I hate that.

Thanks for your helpful comments, I know there are guys here who have all the answers, and I hope you will be willing shed some light on this.

BS.

 

[Beerslayer]

Oh, here's that pic again. Yep. I did that. All $95 of it.

 

[PeterD]

So if I may summarize. And I may, since this is a monologue at this point.

1. I failed to install the jumper on the VR between T3 & T4. This is required if your input voltage is 120vac which mine was. Well 107vac, close enough. So for those of you conversant in the TwitterVerse, that was a #fail. For the rest of us, disregard #fail.
...

First, great thread, even though it was probably hard to do! Hats off to you for posting it.

How does that jumper work? Well, based on my life as a (OK, part time) EE, I suspect that there is a voltage divider resistor set on that sense line coming in. The divider is configured for 240 volts, and then using a pair of resistors instead of just one, they short out one of the pair to allow 120 volts to give the same output. Easy enough to do.

Why does (did) it fail...

Again, without a complete circuit analysis, I think what happened was that the regulator wanted 240 volts, but the 120 it was getting was too low. So it kept cranking up the field drive trying to get to 240 volts. That would, of course, never happen! Now, I'd thought these units did have a fuse in series with the field output from the regulator, but either that fuse was bad, or they don't have one. Again, I don't have one of those regulators to take apart and do an analysis (so much of my comments above is speculative!)

 

[sewerzuk]

Excellent read! Almost like a Pat McManus short story!
I wish I knew more about the internals of that VR; but I don't. The best I could offer is speculation.
What I am really interested in is if this will work when you try it again. Hopefully somebody here has some experience with that VR and they feel like sharing their knowledge. Incinerating $100 bills is never any fun...

 

[Isaac-1]

I think I am going to attempt to repeat this experiment, however I will do a couple of things differently,

1 I will use a terminal strip and connect through it like the way the original VR is connected, so I can roll things back if needed.

2, I will add a small fuse to the F1/F2 connection.

3, and of course I will add the missing 120V jumper.

Ike

 

[gimpyrobb]

Wow, I don't know how I missed this thread when it was posted, but you get a "golf clap" from me! Great thread.