Powerwise charger problem

[wolfejeremy24]

I have a 36V electric EZGO cart and went to charge it for the first time after sitting in the garage all winter. As soon as I plugged in the charger to the wall (not plugged into the cart) there was a very loud pop and a small puff of smoke that came out of the charger. Also blew the circuit in my garage. I took off the cover of the charger and noticed that something had blown on the input board. There are two blue circles about the size of nickels and one of them blew. I ordered a new circuit board and installed it and as soon as I plugged it in the same thing happened. Can anyone please tell me why this may be happening? Also wondering if I can just buy that part and replace it on the board instead of buying another board. Any help is greatly appreciated. The charger is a 36V PowerWise model 28115 G04

[wolfejeremy24]

Here are pics.

[Volt_Ampere]

That component looks like a MOV (Metal Oxide Varistor) It is a transient suppressor. You need to replace it with one that has the proper voltage and surge rating. Not sure why you would blow two of these. I believe that you will find that it sits across the input power wires.

[JohnnieB]

Check the Voltage at the wall outlet.

That MOV (Part number S20K150) is rated 150VAC (RMS) and 200VDC, so one of those two voltages is being exceeded.

You can just replace the MOVs, but until you find and correct the root cause, they will continue to blow.

Personally, I'd replace them with S20K250 or S20K300.

[yurtle]

Question for JohnnyB. I've always heard that MOVs are only good for so many events, they fail due to cumulative damage. Is that true?

Also, I've heard that if the above is true, they get more and more sensitive, until they fail. True?

I do know that they fail closed, like a little suicide bomber, but a noble one that gives his life to save downstream circuitry.

[JohnnieB]

Yes, they have a limited lifespan. It depends on the voltage and current of the spikes.

The breakdown voltage gets lower every time they do their thing.

They may fail closed, but the short converts to an open if the breaker doesn't trip first.

------------

About twenty years ago, the IT department at the hospital I was working in, tossed out some ancient Tripp-Lite Isolators because there was a nearby lighting strike and a bunch of computers wouldn't power up afterwards because the breakers in the panels kept tripping. They finally figured out the the isolators were bad and replaced them with new ones.

I latched onto some of them. They have coils made out of 14Ga magnet wire wrapped around powered iron cores, MOVs, illuminated switch and either two or three standard duplex outlets. I replaced the MOVs and I'm still using them as multi-tap extension cords for my audio, video and computer stuff. (They fed UPSs on some of it.)

[yurtle]

[wolfejeremy24]

Thanks for the replies. The same MOV blew on both of the input boards. The other MOV on both boards are fine. I haven't checked the voltage at the wall outlet yet, but other electronics that I plug into that outlet work fine. I just didn't know if there could be anything else wrong with the charger itself that would cause both of these same MOVs on two different boards to blow.

[JohnnieB]

My guess is that they are just connected across the hot and neutral lines.

Can you post a picture of the back side of the board?

Actually, you take pretty good pictures, so could you post some straight down shots of both front and back sides of boards.

I'm trying to figure out what the trim-pot does. (Adjust Cut-off voltage?)
My PW-II has a potted control board and I cant see anything on it.
----------
Also, some shots of how the control board and transformer are wired.
I don't think it is possible to miss-wire the transformer to blow the MOVs, but something is.
The odds of the same MOV on two different board blowing is pretty high, and other things plugged into same outlet aren't smoking, so I'm grasping at straws.

[Volt_Ampere]

Mov's can only take very short duration overvoltage transients. If you exceed their power rating, they overheat and blow. I have never been a fan of these things. You could take the good one from your old board and swap it into the bad one on the second board. I am sure that the two are the same part. Something is spiking your input voltage if it keeps blowing these things. They are really there to save the board from damage if there is a short spike on your power line. I have seen them take themselves out many times.