MEP-802 and 803 Main generator tip.

[jimbo913]

I am confused by the MOV addition. I thought that the quad winding issues were resolved by the slow blow fuse modification alone.

 

[Chrispyny]

I am confused by the MOV addition. I thought that the quad winding issues were resolved by the slow blow fuse modification alone.

I believe the fuse protects the stator if the diode bridge fails. The MOV protects the diode bridge. So the fuse is a back up in case the diode bridge fails.

 

[Chrispyny]

Also, i can't thank you enough Kloppk for all your help. Many guys here like myself love these machines, but i'm 38, work full time, and have little to no extra time after work ro research any of this stuff. You make it VERY easy. You are our 'R and D' department!!! Thanks SO much!!!

I was going to buy the parts last night on amazon but ran out of time. I'll order the parts and make the mods asap. I did chdck my control box and there is NO mod currently.

 

[kloppk]

...I was going to buy the parts last night on amazon but ran out of time...

Instead of ordering the MOV's I'd be happy to mail you a couple of them. I only used 1 of the 10 I purchased.
If you'd like a pair of MOV's PM me your mailing address and I'll pop them in the mail to you.

 

[Chrispyny]

Just wanted to say thanks to all who helped me with this mod, it's all set. It's crucial to me to ensure a happy life for my very expensive generator.
Very easy to do. The lower left screw for the voltage regulator is captive as Kloppk had advised me. No need to worry about a bolt falling off in the back of the control box when unscrewing it. The screw is plenty long enough to reuse and the fuse holder fits perfectly in that location.
I didn't have 16g white wire so i used the 12g thhn that i had on hand. I hope that won't be an issue. The fuse holder was like $11 and the fuse was $29!! It cost a total of $42 approx locally. After shipping, it made no sense to order via amazon or online. Even with my amazon prime, the price would have been the same.
I simply removed wire 8 from the Voltage Regultor and slipped it onto the lower screw of the fuse older .. then added the new wire from the top of the fuse holder back to the #8 screw on the VR.

 

[jimbo913]

Looking good. I have never heard of bigger wire being a problem. I need to get the MOV's ordred, just waiting until I have enough junk in my cart for free shipping.

 

[Guyfang]

That is a text book classic example of how to do this mod, and looks very much like the first ones I saw in 2009 in germany, done at Germersheim. Perfect!

 

[lonesouth]

Can someone explain this to me a little better? In the OP article, it states that the quad windings circuit is cooked by the fault, without the fuse. In link from Hard Head, it is the exciter windings, which overheat due to the AVR getting fried by the quad windings voltage and allowing too much current to the exciter, creating thermal expansion of the rotor such that the rotor impacts the stator.

 

[kloppk]

The link from Hard Head applies to issues and fix for the 805A/806A/815A/816A generators and NOT the 802/803.

Here is my understanding with the issue with the 802/803....
Their A1 voltage regulators are powered by the quad winding. The quad winding provides AC power to a diode bridge inside A1.
Occasionally the voltage output from the quad winding can get to high for the diode bridge causing the diode bridge in A1 to short out.
The shorted diode bridge causes a short across the quad winding output (in the stator) which causes the quad winding to overheat and burn out destroying the stator.
Once this happens BOTH the A1 voltage Regulator and the Quad Winding are damaged requiring replacement.

The "Fuse Mod" places a fuse in line between the Quad Winding and the Voltage Regulator.
If the high voltage condition occurs and the A1's diode bridge shorts out the fuse blows protecting the Quad Winding from damage.
So with the Fuse Mod the Quad Winding is protected but the A1 voltage Regulator is still damaged.

The MOV mod takes the protection a step further. The purpose of the MOV mod is to protect the A1 voltage Regulators diode bridge from shorting out by clipping any high voltage spikes from the Quad Winding.

Apparently the root of the problem stems from a poor design of the A1 Voltage Regulator. The PRV (Peak Reverse Voltage) rating of the diodes in the A1 voltage regulator are too low a voltage rating making them subject to shorting out due to voltage spikes. Diodes can fail if they are exposed to reverse voltages in excess of their PRV rating.


The diode bridge in A1 are the 4 diodes in the upper left corner.

 

[lonesouth]

that makes sense.

so if the A1 burns out and the quad winding burns out, why can't you use something like a sx460 regulator and power it from the main stator output? the field flash circuit would initiate the field in the exciter and thereby generating main output powering the VR which could take over when the master is released back to run. or is the whole stator destroyed in the demise of the quad winding?

 

[Korgoth1]

When the quad winding goes, it burns up everything from what I understand.

Has anyone replaced the diodes in the avr successfully yet?

 

[DieselAddict]

When the quad wingdings go out you are totally hosed. No VR is possible. You would have to get that rewound or replace the rotor.

 

[lonesouth]

10-4, I bet that is easy to get to and cheap to have rewound.

 

[Guyfang]

Perfect explanation KLOPPK!

The big problem in the beginning was that NOTHING in the manuals suggested to the repair personnel what the CAUSE of the problem was. So when people found the Quad winding burnt out, they simply put in a new stator, or even a main AC. Started it up, and had the same problem. Some units even did it multiple times! Part of the problem is that repair personnel are fixed on the SOLUTION, and forget the CAUSE. Putting in the quad protection fuse allowed the government to continue to use poorly designed A1's until the stock ran out. THEN the "improved" A1 could be procured.

 

[lonesouth]

course, none of this should be a problem with the MOV across the quad winding outputs, right? So a $0.05 item protects a $20,000 generator.

 

[csheath]

Perfect explanation KLOPPK!

The big problem in the beginning was that NOTHING in the manuals suggested to the repair personnel what the CAUSE of the problem was. So when people found the Quad winding burnt out, they simply put in a new stator, or even a main AC. Started it up, and had the same problem. Some units even did it multiple times! Part of the problem is that repair personnel are fixed on the SOLUTION, and forget the CAUSE. Putting in the quad protection fuse allowed the government to continue to use poorly designed A1's until the stock ran out. THEN the "improved" A1 could be procured.

So there is an "impproved" A1? What year was it installed?

 

[Hard Head]

Some info on the diodes used IN5406. I replaced the diodes in the units I service with IN5408. The peak reverse on the 5406 is 600v and the 5408 is 1000. The normal voltage is 700 vs 420. Everything else is roughly the same. See chart

 

[Guyfang]

So there is an "impproved" A1? What year was it installed?

I didn't say it was installed. I said "Then the "improved" A1 could be procured". Big difference. As far as I know, it was never "procured". But the only way to tell, would be to check the spec's in the FEDLOG, or maybe compare and OLD volt reg, to a new one. The part number "SHOULD" be different. Can someone look at a volt reg and tell me the part number thats on it? We can take a gander. I have and OLD parts manual to check it against.

When the government spends umpteen kazillion bucks on spares, for a items like the A1, they are NOT going to toss them out and order new ones. Nor are they going to send in a "cheap" item like an A1 to be upgraded. The upgrade process would probalöly cost more than the original A1 cost new. They did the simplest thing possible. Put off the problem by installing the fuse. And they were right in doing so. The military spends money like drunken sailors. For once, they saved us a bit. The Quad Fuse MWO has been out at least 6-8 years. In theory, every set should have been upgraded twice by now. If not more often. It just begs you to ask someone, WHY?

 

[NormB]

Checked mine out today, Letterkenney reset fall 2009 (? October, I forget, wrote it down somewhere), the PS mag update/mod came out in May? It's there, just to the left of the A1 rebulator but they used this really weird fuse: Littelfuse Brand KLDR 3 (KLDR-3) 3 Amp (3 A) 600V Midget Time-Delay fuse, available through amazon (what isn't?) for $6.00 each.

Poked around inside the unit some more (I bought it in June), had to vacuum out mouse nest(s) above the stator - there's a panel with an inch gap behind it and some wiring harness bundles in front. I'd have to remove the top front panel to get to that space (forward of the diode board panel) and see how many mice bodies are inside and if they destroyed any wiring. I have the same problem with a log splitter, effing mice nest under the fan housing on the engine every year and I've taken to wrapping hefty garbage bags around the engine and duct-taping them closed. Mice STILL get in. I might put a trap inside the generator...

 

[DieselAddict]

Mothballs. The old stinky kind if you can find them. They work wonders for running off mice.

Edit - Old school naptha mothballs. I can offer first hand experience that those work to keep mice away.