How to test a Bridge Rectifier?

Question

Could someone please help me by explaining to me how to test a 35 A 4 point bridge rectifier.

Answer 1

A bridge rectifier is 4 diodes. Test them as such. A diode conducts in one direction and not in the other.

Any simple continuity tester or mutli meter can be used.

Usually when diodes fail they start to conduct in both directions and you know its bad because it blows fuses, trips the breaker etc supplying it.

Site showing a drawing of bridge rectifier - http://www.tpub.com/neets/book7/27c.htm

Answer 2

If you are testing the output of the bridge rectifier with NO LOAD on your testing device, then it is possible that you could see a sine wave at the outputs (-) (+). A rectifier blocks CURRENT from going in the reverse directions. But if there is no current flow (load) there is nothing to block. It would be like measuring the output of a battery with a resistor in series, but no load. The voltage will measure full battery voltage because, without current flow there is no voltage drop across the resistor. The voltage drop (loss)across a resistor is V=IR; but if I is 0, the voltage drop (loss) is 0. Similarly, without current going through the diodes, you may see full AC at the output. Even WITH current flow, you would see RECTIFIED AC (half wave AC), or DC, at the output. Don't confuse half-wave as an AC signal, even though it is not straight DC. You need a filter circuit to do that.

Answer 3

Take a multi-Meter and switch it to Ohm x 1
Test between one of the "~" and "+" legs.
You should get either an almost-zero reading in one direction, and when you reverse the test probes, you should get an almost infinite ("sleeping 8") reading.
Now try the same between this "~" leg and "-".
Same as above.
Now repeat the same tests with the other "~" leg, and "+", and then "-".
Same as above.
If you either get almost zero or almost infinite in BOTH directions, then the rectifier is fried.

Answer 4

Using an oscilloscope to check the output, send a sine wave through it using a sig gen. The output should be a uni-directional wave which will swing from 0 to +Y to 0 for each swing of the input voltage from 0 to +Y to 0 and 0 to -Y to 0. input --\/\/\/\/\/\/\-- output __/\/\/\/\/\__ A half-wave rectifier will only produce output on the positive swing of the input sine wave. --/\/\/\/\/\-- __/\_/\_/\_/\__