Trying to repair Schauer 12V car battery charger

[Superspark]

Hello I accidentally arced my battery charger that worked yesterday. I hear the transformer humming, but no voltage at the leads. I think the problem may be the disc diodes, but am not sure. I would like to repair this as cheap as possible even if the circuit becomes changed. Any help would be greatly appreciated. Thanks

https://www.flickr.com/photos/128266543@N05/

 

[crutschow]

You likely zapped the round device pressed into the heat-sink which I think is a Triac.
Where are the output leads to the battery connected?

 

[Superspark]

Thanks for the suggestion. I checked the diodes in got about .481 volts for both of them.

You likely zapped the round device pressed into the heat-sink which I think is a Triac.
Where are the output leads to the battery connected?
One lead goes to the DC ameter and the other lead goes to what I think is a fuse on the bottom black plastic device with 10A 12V printed on it. The fuse plastic thing has continuity through it. Thank you.

 

[KeepItSimpleStupid]

The two terminal thing at the bottom is circuit breaker. Sometimes they are self resetting and may click.

I don;t see any >6A diodes.

Check to see if an AC voltage is coming out of the leads rather than pulsating DC.

That 3-leaded device (2 leads and a stud) may be an SCR and it does both the half wave rectifying and turn off.

There isn't much there, so tracing the circuit out, would be your best bet.

 

[Superspark]

I have 28.1 AC volts coming out the secondary. What should I do from here?

 

[4pyros]

I have 28.1 AC volts coming out the secondary. What should I do from here?

Test the diodes.

 

[KeepItSimpleStupid]

Not the secondary, but where the battery goes? Normally, that should see pulsating DC.

Take you ohmeter with the power off and measure from the chassis to the larger tab. I suspect this is shorted.
You can also try the diode test on the same terminal.

So, what I THINK is happening is your applying AC to the battery clips and probably 28 VAC.

Thanks for the secondary measurement.

 

[KeepItSimpleStupid]

I agree with 4pyros, the MR2502? https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCkQFjAA&url=https://www.onsemi.com/pub/Collateral/MR2500-D.PDF&ei=BimOVIrbDsOfNr2ThMAP&usg=AFQjCNEGl4P_b44h1F2J3QcLYeQ1dDLR5Q&sig2=D5cSN0QBz54riaM_BH47WA&bvm=bv.81828268,d.eXY&cad=rja diodes need to be checked. You diode test on your DMM is the best way. I missed the diodes originally.

Pull the faston when you do. Test (Case to tab) in both directions.

Take a better picture so that the entire chassis is is visible so we can wire trace.

AT this point, the charger looks simple. Transformer, ammeter, circuit breaker, 1/2 bridge rectifier (two diodes), an SCR/triac that stops the charger. Can't tell if it's on the DC or AC side, but both will work because it's pulsating DC.

When you measured the output, you assumed DC. Check for an AC voltage.

 

[Reloadron]

You have two enameled wires off the transformer going to what looks to be a pair of heat sink mounted diodes. Those two wires should be the transformer secondary. Is there a third wire which would be the transformer secondary center tap? The 28 VAC makes sense if a secondary center tap is used with the transformer. Using two diodes plus a center tap would yield about 14 VAC each side of the center tap so that makes sense as the rectified DC would be about 14 volts less the forward diode drops. I also agree the small rectangular box is likely a circuit breaker that is thermal. It should reset once it cools down following a short. Try and measure the resistance across it. Do the two what I suspect are diodes have diode symbols on them and if so is the cathode (line) on the side mounted to the plate? That would be my guess. The two terminal device mounted on the plate with the diodes is likely a SCR and the small glass thing that looks like a tiny diode is likely a Diac connected to the SCR Gate. Now if you can find a secondary center tap measure from the center tap to the plate the diodes are mounted on. You should see about 14 or so volts DC.

Ron

 

[Superspark]

Okay, I figured out I was mis-testing. I found that if I connect the negative on my meter to the negative clip on the charger I find my 12VDC on the metal plate not on any of wires or tabs. I eventually traced the 12 VDC though the back of the amp meter on the battery charger. Last place to look was on the positive lead/clip of the battery charger, and I had no current there. Found out I had a frayed or cut wire right where the wire ties onto the chargers positive clamp. Sorry about the confusion, I'm just not really used to using my meter. Anyhow I got the charger from my grandfather who probably had it for 50 years, so I'm happy to report it lives on, and now he can stop rolling over in his grave. Thank you all. Bob

 

[KeepItSimpleStupid]

Thanks for the update.

 

[Reloadron]

Anyhow I got the charger from my grandfather who probably had it for 50 years, so I'm happy to report it lives on, and now he can stop rolling over in his grave. Thank you all. Bob

Glad it all worked out. I have a similar old charger like that in my shed last I saw it and those things don't die easy. The one I have will likely be working just fine long after I am gone.

Ron