Help idinifying circuit from Battery Charger

[davg]

The photo is of a circuit in an older car Battery Charger. I was wondering if someone on here could identify this circuit and explain it's function and how it works. It seems to be a very simple circuit to convert AC power to DC power. The two leads from the Transformer connects to the two terminals

[R_J]

Re: Help idinifying circuit from Battery Charger

There should be button diodes mounted under each of the brass tabs. 4 diodes making up the bridge rectifier.
The diodes are likely similar to ar504

[davg]

Re: Help idinifying circuit from Battery Charger

There should be button diodes mounted under each of the brass tabs. 4 diodes making up the bridge rectifier.
The diodes are likely similar to ar504

What should these diodes look like? there is something under these tabs that look like doughnuts?? Can I use a bridge rectifier as shown below to replace that circuit?

[davg]

Re: Help idinifying circuit from Battery Charger

There should be button diodes mounted under each of the brass tabs. 4 diodes making up the bridge rectifier.
The diodes are likely similar to ar504

Tks again R_J yes there are?? first time a have seen a diode looking like that?? The circuit seem to be shorted is there a way to test these diodes?

[R_J]

Re: Help idinifying circuit from Battery Charger

Each diode can be tested with a multimeter and diode test. What seems to be shorted? the diodes?
It looks like all four diodes have a common point, the aluminum plate, so they could have 2 diodes in parallel

[davg]

Re: Help idinifying circuit from Battery Charger

All 4 of these has a slit in the outer casing which I assume is not normal. Testing with my meter in diode mode and leads end to end gives no reading and the same when I reverse the leads?

[R_J]

Re: Help idinifying circuit from Battery Charger

I don't believe they should be split like that, what is the number on them? it should be marked on the side. I t could be the diodes have a high forward resistance so they could show open with a meter.

[davg]

Re: Help idinifying circuit from Battery Charger

No numbers visible on either of the 4?

[R_J]

Re: Help idinifying circuit from Battery Charger

People sometimes replace them with 50 amp/400v D0-5 style stud mount diodes

[redwire]

Re: Help idinifying circuit from Battery Charger

It looks like the charger manufacturer tried to copy a car alternator's construction with press-fit diodes. But the plastic washers are terrible for heat conduction and aluminum rivets on copper likes to corrode and the skinny wires have to go. Yuck.

I would change over to a bridge rectifier module like KBPC5010 50A 1000V $3.00
But the big problem really is heat sinking the diodes. Even if you put in huge expensive stud-mount diodes, that small plate just can't get rid of heat very well. I would beef up the heatsink.

How many amps is this charger rated? Does it have a fan?

[davg]

Re: Help idinifying circuit from Battery Charger

People sometimes replace them with 50 amp/400v D0-5 style stud mount diodes

I have a couple of these on hand #72HF80M would they do the job

[davg]

Re: Help idinifying circuit from Battery Charger

It looks like the charger manufacturer tried to copy a car alternator's construction with press-fit diodes. But the plastic washers are terrible for heat conduction and aluminum rivets on copper likes to corrode and the skinny wires have to go. Yuck.

I would change over to a bridge rectifier module like KBPC5010 50A 1000V $3.00
But the big problem really is heat sinking the diodes. Even if you put in huge expensive stud-mount diodes, that small plate just can't get rid of heat very well. I would beef up the heatsink.

How many amps is this charger rated? Does it have a fan?

15Amp 12 & 6 volt 100 amp cranking

[redwire]

Re: Help idinifying circuit from Battery Charger

Any diodes used need heat sinking for cooling. This is the hassle.
With a 15A load, each diode will dissipate about 7W of heat, roughly.
If you use a bridge rectifier module, then all the heat is concentrated in one square for 28W.

The VS-70HF is a large 70A 800V stud-mount diode, you would need four.
But the hassle is mounting them on the heatsink, the cathode is the bolt so two of the four diodes need insulators or the special version with reverse-polarity (anode to case). Insulators can't transfer the heat, so the diode cooks or the plastic melts and they aren't a great way to go.

Simplest fix I think is bolt a 25-50A bridge module on the heatsink, the modules are isolated case so no more hassles with shorts to the metal.

Rectifiers from a scrapped PC power supply could work. They are two Schottky's in a TO-220 case and a bit more voltage for the battery. What else you got in the junk box.

[eccerr0r]

Re: Help idinifying circuit from Battery Charger

Yeah probably best not to use a bridge and use discrete diodes - the original design spread the diodes out away from each other for a reason.

and holy crap, seeing some china shops selling the button diodes for less than 10 cents a pop in 1000 quantities... wonder how bad they are?

[davg]

Re: Help idinifying circuit from Battery Charger

Any diodes used need heat sinking for cooling. This is the hassle.
With a 15A load, each diode will dissipate about 7W of heat, roughly.
If you use a bridge rectifier module, then all the heat is concentrated in one square for 28W.

The VS-70HF is a large 70A 800V stud-mount diode, you would need four.
But the hassle is mounting them on the heatsink, the cathode is the bolt so two of the four diodes need insulators or the special version with reverse-polarity (anode to case). Insulators can't transfer the heat, so the diode cooks or the plastic melts and they aren't a great way to go.

Simplest fix I think is bolt a 25-50A bridge module on the heatsink, the modules are isolated case so no more hassles with shorts to the metal.

Rectifiers from a scrapped PC power supply could work. They are two Schottky's in a TO-220 case and a bit more voltage for the battery. What else you got in the junk box.

Tks Redwire but I only have two of these vs-70hr's kicking around so I guess that's out? I just recently converted an old PC power supply that I had kicking around to a bench top power supply but I do have a couple of power supplies from a TV receiver not sure what I could get out of that? These board delivers a bunch of voltages but since I am not a tech person I am not sure of the value of what I have in my junk box?? I derive a lot of satisfaction from taking scrap and turning it into something useful but most of my knowledge come from the great people on forums like this. I am a knowledge seeker.

[stj]

Re: Help idinifying circuit from Battery Charger

you could do a modern design with mosfet rectification - voltdrop in the microvolts!!

[davg]

Re: Help idinifying circuit from Battery Charger

you could do a modern design with mosfet rectification - voltdrop in the microvolts!!

A little over my head?? Trying to work with what I have but maybe you could provide a drawing

[R_J]

Re: Help idinifying circuit from Battery Charger

Or buy a new charger when they go on sale.

[stj]

Re: Help idinifying circuit from Battery Charger

lol - that too.

[davg]

Re: Help idinifying circuit from Battery Charger

Thanks for the comments guys and of course you're right but it's not about the charger,, if it works I will proberly find someone who needs it?? for me it's understanding and accomplishment. I have already learned what that circuit was but I am still not sure how it works? It would appear that the four diodes in that circuit is flowing from anode to cathode or was two reverse polarity?? These button diodes seen to be color coded with a brown side? I will try to find a datasheet for them.