# How do I test a bridge rectifier?

I got a mess of components at an auction a couple weeks ago, including an unmarked box of unmarked bridge rectifiers. They're about 1" square & 1/4" high if that makes a difference in terms of an input voltage for testing. I don't know if there are ANY inferences that can be made from size, shape or color. The bottom has the typical one blade that's oriented perpendicular to the other three.

What is the best way to figure out what I've got? I'm not a big fan of the "if it smokes, that's too much voltage...back off a titch and see if the next one smokes" method.

UPDATE: I found a scribbled note in a box of capacitors marked "40/50v Rect", and sure enough, they all test in that range. Now I've just gotta figure out what to do with 'em. Amperage experiments coming up next, but I'm at least confident that I'm starting from a place where nothing will explode. Too much. :)

• Can you please upload a clear photo showing the pins and the two flat sides of the packaging? Jul 27, 2012 at 13:54
• In general, electronic components without a datasheet are next to useless. Are you sure the packages contain no markings at all that could lead you to a part number? What about posting a picture? Jul 27, 2012 at 13:55
• I have the book/catalog form of this: nteinc.com/rectifiers/bridge.php?a=12 - so a picture and some dimensions/measurement will help a lot. Jul 27, 2012 at 14:00
• I will post images tonight when I get back to my studio. Images I can do... :) Jul 27, 2012 at 14:25

Apply current from an N amp variable supply across 1 diode.
Plot voltage drop against current.
A reasonable guide should be gained.
A say 5A device should have Vdiode < 1 Volt and maybe < 0.8V.
Once you get a 1st estimate try the same with a diode of known rating and see how it compares.
eg if 1V at 5A try a 5A diode and see what Vf is at 5A.

Run at various currents and note steady state temperature.

Use variable voltage supply in series with largish resistor applied in non conduction direction.
Increase voltage and note rectifier leakage current.
As you approach rated value it should get uncomfortable.

From voltage drop under current, and heating with current and leakage with reverse voltage you should be able to establish a safe operating zone. \

Please provide photo & exact dimensions.

Like drxzcl says they're of little use without datasheet. The square types usually can handle quite a few amperes, but you can't say if that will be 5 or 10.
To give you an idea of the possible range, this rectifier is about 1 inch square and available at current ratings from 12 A to 35 A:

Nevertheless you can easily find out how the diodes are connected if you have a multimeter at hand. The multimeter usually has a diode test function:

When the test probes are connected as shown the meter gives you the diode voltage drop, it the probes are switched you'll get an open connection indication.

So suppose you connect the + to one pin, and try the - on the others. If you have a reading on two of the pins that means that the + is connected to the left pin of the rectifier shown. You can verify this by placing the - on the remaining pin and check the two other pins again. You should again get a reading for both. Then the - is the right pin in the drawing. The other pins may be mutually switched.