Help me fix my Battery Charger

[kittysmitty]

My battery charger had a puff of magic smoke and a couple of sparks out through the fan. On close inspection I found a resistor badly burnt. This is on the AC input side. Any idea what the specs might be for a replacement. Its a 25 amp Canadian Tire automotive charger. Its R3 that's burnt. The charger was being plugged into a generator that has questionable output voltage, it wanders. Thanks

[mab]

I'd guess it's a varistor - I guess there are no identifying marks still visible? if the input volts were a bit high that could explain it's demise.

Can't help with specs, sorry, but if I understand the circuit layout though, the charger should still work without it.

[dnix71]

My thoughts too mab except that the varistor is inline with the hot side. If you blow the vr then it shuts down everything.
The mechanic at work plugged a lamination cutter into the wrong voltage and it smoked a vr. If you know the value you can just buy another and solder it in.

If Canadian Tire sold this there must be others around. The clamping voltage and surge capacity is what matters.

[OperaHouse]

That is a varistor used to protect against high surge currents when capacitors first charge. It goes from about 20 ohms down to less than one when hot.  Many manufacturers delete these or put 1-2 ohm resistors in place.  You have a 1 in 500 chance it just went bad  and replacing it will make it work again.    Most likely the FET or diode has shorted out.  Include pictures of the rest of the board.  Assume you have a meter.

[kittysmitty]

Here are pictures of the complete board. Doesn't appear to have any other damage. I have not had a chance to see if it still works. Thanks

[OperaHouse]

First test you can do is see if a short exists between those two large parallel traces going to the black rectifier on the heatsink.

Second check for a short between the other two leads of that black rectifier.

Third you can safely check it powered up by placing a 100W (or two parallel 60W] lamps in place of the varistor.  No or dull glow indicates it is likely OK.  Bright glow indicates a short.

[mab]

at the risk of stating the obvious: I think there's a fuse next to the black and white wires (behind the big red cap in the 1st pic) - check it for continuity.

My thoughts too mab except that the varistor is inline with the hot side. If you blow the vr then it shuts down everything.

Are you sure? It looks to me like the VR and R1 are across the two long vertical tracks in that solder-side pic - which I see as hot & return.

[kittysmitty]

Well I finally got around to doing a little more testing. With a battery hooked up  and using my battery tester, the charger will put out it's full 25 amp output. It appears it's working fine.
That said, the component on the circuit is destroyed, and I'm sure it has/had a purpose.
What's everyone thoughts? Don't worry about it? Or try to find the specs and replace it. It looks like it's in parallel across the AC input.
Thanks

[joestue]

it was most likely an MOV, and you should replace it with a standard 330v rated type, its a surge protector and how large of a replacement you buy is totally up to you.

you can buy one, or a whole bag off ebay for the same price if you're lucky.