Query About Rectifier Diode

Thread Starter

Sam_B

Joined May 30, 2021
3
Hi...I am facing an issue with my rectifier diode. When I tried to check the continuity , Pin 2 and 3 is showing value 1 from both side of multimeter...Does it mean that the diod is damaged ??
 

Tonyr1084

Joined Sep 24, 2015
6,000
First, welcome to AAC.

Now, are we talking about a Bridge Rectifier?

A diode is checked on the multimeter using the "Diode Check" setting. When reading one way through the diode it should typically read somewhere around 0.450 and should have NO reading when reversed. If it tests out that way then it's good. But if it reads in both directions then there's a problem. If it reads close to zero then it's shorted.
 

Tonyr1084

Joined Sep 24, 2015
6,000
HERE is one kind of Bridge Rectifier (BR)

HERE is another type of BR. There are yet more styles; but they all do the same thing.

Note: The links have been sanitized. No tracking.
 

MisterBill2

Joined Jan 23, 2018
8,808
That reading of "1" is probably an over-range indication of the ohm meter, and so no, you did not damage the power diode with the meter. On most ohm meter settings most digital meters should read open in one direction, and some will read open in both directions. Diodes are not zero resistance in the forward direction, they do require some voltage to start conducting. For most regular power diodes that voltage will be about 0.7 volts. If your meter has a diode test mode, that will be the one to use, if not, you can check by using a 9 volt battery and a series resistor of at least 1000 ohms connected across the diode. Then measure the voltage across the diode with your meter. In the forward direction you will read less than a volt, in the reverse direction you will read very close to the battery voltage. That will show that the diode is OK.
 

MaxHeadRoom

Joined Jul 18, 2013
23,150
The resistance range on most VOM is not enough current to forward bias the diode, you need a diode check range that uses current through the diode to test the volt drop across it.

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Thread Starter

Sam_B

Joined May 30, 2021
3
First, welcome to AAC.

Now, are we talking about a Bridge Rectifier?

A diode is checked on the multimeter using the "Diode Check" setting. When reading one way through the diode it should typically read somewhere around 0.450 and should have NO reading when reversed. If it tests out that way then it's good. But if it reads in both directions then there's a problem. If it reads close to zero then it's shorted.
Thanks for your Reply . Actually I was testing this item . I was checking continuity between pins...Such when Pin 1 with -ve end and pin 4 with +ve end of multimeter I got some value but after swiping +ve and -ve end , the value was 1.

But in case of pin 3 and pin 4 , in both cases , the continuity value was 1.
 

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Tonyr1084

Joined Sep 24, 2015
6,000
Pin 1 is the POSITIVE (plus) side of the output and Pin 4 is the NEGATIVE side. Pins 2 and 3 are the AC inputs. Also, you identify which is pin 1 by the cut corner on the top right.
1622418009607.png

This is the schematic diagram of what you MIGHT have for pin wiring.
1622418331125.png
It will be something similar. Whichever, pins 2 and 3 are they are each Anode ends of the individual diodes with respects the positive pin within the BR and Cathode ends of the individual diodes with respects the negative pin within the BR. You measure between Pin 2 and Pin 1 both ways. One way you should get some reading between 0.400 and 0.600 (but that's just a guess - still, it's what I would expect from a good rectifier. Next, do the same with Pin 3 and Pin 1. Again, both ways. Look for a good reading one way and apparently a "1" the other way according to your meter type. THEN check between Pin 4 and Pin 2 both ways. Finally, check between Pin 4 and Pin 3 both ways. One direction you're going to see the expected value somewhere within that range I mentioned. If you're a little outside that range it's probably still good. But a "0.000" or very close to that reading then you have a shorted diode. The BR is bad in that case.

Take your measurements and carefully note what you get when you test all eight scenario's then report them to us. We'll likely know if it's good or bad. Few years back I had a BR go bad on me. It went dead short on one of the four internal diodes. The ONLY fix was to replace it. I replaced it with a diode with a slightly bigger rating. Darn thing has been working just fine these few years.
 
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