I was trying to figure out why a car battery starter/charger (input 220V, output 12V wasn't working and when I opened I try following the wires to see what the circuit is, but then I run into these plates and I've got nothing, The negative output is connected to one of the plates, but the positive is connected to both of them which is what confuses me the most.

I don't have a schematic, I'd be checking that if I did, I think the reason it doesn't work is because the cable from the positive which appears as it should be connected to both plates has cut the connection to one of the plates, but that's beyond the question. I'd like to know what these plates are and what purpose they serve.

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  • 2
    \$\begingroup\$ That's got to be the rectifier assembly, but the wiring is too jumbled to discern details other than the fact that the ends of the transformer secondary appear to be connected to each plate, which would probably make sense. \$\endgroup\$
    – Dave Tweed
    Apr 8 at 3:49
  • \$\begingroup\$ There's probably diodes bolted to them; the metal plates are heatsinks for the diodes. \$\endgroup\$ Apr 8 at 11:49

The metal plates are heatsinks for, and terminals of, the rectifier,

The thing with 50 written on it is a press-in diode.

  • \$\begingroup\$ Shouldn't there be 4 such diodes then? I only see 2. Or are the other 2 on the other plate perhaps. \$\endgroup\$
    – Lundin
    Apr 8 at 10:19
  • \$\begingroup\$ You can make a full wave rectifier with 2 diodes, and a suitable transformer (centre tapped secondary). But the 4 holes suggest the intent was to fit 4 diodes, but 2 were moved to a second plate because one heatsink wasn't enough... \$\endgroup\$ Apr 8 at 11:50
  • \$\begingroup\$ Those where indeed diodes and there was a fourth one I wasn't seeing, now I can see how that's a bridge rectifier \$\endgroup\$ Apr 8 at 14:05
  • 1
    \$\begingroup\$ you need two plated because the plate are also terminals, and in a bridge rectifier half the diodes connect to each terminal \$\endgroup\$
    – Jasen
    Apr 9 at 0:35

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