Karl's Power Supply SCR question?

I saw the photos -- but it was not clear from the photos that all the SCRs were the same part number -- just the same family of parts. It could easily be that half of them are grounded cathode and half grounded anode parts. The part numbers were not visible in the photos. :-)

The test would be whether one wire of each pair feeding a gate is shorted to the stud in *every* SCR. If not, then some are likely grounded anode -- and that would actually make sense to make a bridge rectifier. I would expect the black wire to be the one connected to the cathode, but I'm not sure.

And -- are the studs electrically connected to the heat sink, or are they insulated? Such rectifiers have long been sold with mounting hardware which consists of a pair of large diameter mica washers, a Teflon ring washer to hold the stud centered out of contact with the metal of the heat sink, a flat washer and a nut. Also -- they normally are mounted with a heat sink compound (with or without the insulating washers) to maximize the conduction of heat to the heat sink. Anyway -- if they are mounted with the insulating washers, there will be ring terminals connecting to the studs to complete the circuit.

It really would have helped if you had not stripped it apart. it would work a *lot* better with the original driver board.

Can you still identify the driver board that all those gate connections were connected to?

Don't get rid of them until you are *sure* that you don't need them. You will probably need quite a few of them for this -- and having spares helps too.

I just recently got fifty such relays for future projects.

Good Luck, DoN.

Reply to
DoN. Nichols
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Hmm ... thyristors, not SCRs. And it looks as though the one illustrated has the cathode connected to the heavy-gauge wire, not the stud. Now -- the remaining question is still "are *all* of them the same?"

Part number does not seem to match. Just because it looks the same -- are you sure that it *is* the same?

O.K. According to Wikipedia, "Thryristor" is an alternative term for SRC -- but it also can refer to a bunch of other devices.

Make sure exactly what you have -- by matching the part number, not just by finding something which looks similar. Most of the data sheets for 71RC80 devices appear to be on Chinese sites now, and those are blocked from here.

Good Luck, DoN.

Reply to
DoN. Nichols

They both had it - a pot can adjust the phase trigger voltage. The R-C time constant of the pot/cap combination sets a time delay which equates to a phase angle and at the trigger voltage there is a massive rush of current through the main terminals.

It is all how one looks at it. RC is used with AC power - the load is DC partial wave.

Four terminal Thyristors are used for gate-turn-on and gate-turn-off operation. Two gating - an anode gate to turn it off and the cathode gate which is used to turn it on.

There are many version of Thyristors.

Mart>

Reply to
Martin H. Eastburn

Don't stack the SCR's!!!!!

The are likely high voltage already.

Stacking means putting anode and cathodes end to end.

If you do that - the gates will be floating up at higher and higher voltages. The one you showed us was 400V DC. Likely a 220v gated rectifier.

No manual and no cable set that might lead you to believe the use ?

Mart> >

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Reply to
Martin H. Eastburn

It's trivial. Just connect the gate directly to the anode, and voila! Diode!

Seems kind of a shame that he didn't keep any of the control electronics, however.

Cheers! Rich

Reply to
Richard the Dreaded Libertaria

That violates reverse gate voltage spec. Circuit behavior may not be as expected or hoped for.

Reply to
Don Foreman

Yes, I concur - it should have a diode from gate to cathode to clamp the reverse gate voltage, and of course, a resistor to limit dissipation.

What I had in mind was the time I made a center-tapped full wave controlled power supply, and drove the mongo SCRs with 4Nsomething optos, and just connected them straight from anode to gate, because when the gate fires the SCR, its forward voltage drops to a diode drop.

But there was no direct connection for the negative half-cycle, so based on my experience, I did, in fact, neglect to include the problem of the negative gate voltage.

Thanks, Rich

Reply to
Rich Grise

I looked for mine, but it's missing.

Reply to
Michael A. Terrell

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