Is this a bridge rectifier

[Biggles]

Hello All

 

I think this is a bridge rectifier

 

 

 

 

If so how do I test it. I know its only supposed to let current flow in certain directions.

 

Cheers

 

Biggles

[Ray]

Looks like a bridge rectifier to me.

 

I seem to recall that you can test it with an analogue multimeter on the Ohms setting but I could be wrong.

 

I think that you put one probe on the + or - terminal - the DC terminals - and the other on one of the other terminals - the AC terminals. You should see a needle deflection. You should get a reading with the probes one way round but not the other.

[Rojo]

Hello All

 

I think this is a bridge rectifier

 

 

If so how do I test it. I know its only supposed to let current flow in certain directions.

 

Cheers

 

Biggles

 

 

Yes that is a bridge rectifier. It will convert AC supply to DC output (if working correctly). The AC input is to the terminals marked (as in the picture) by a wavey line ( ~) . The output terminals will be marked + and - . Hope this helps!

[Iain_S]

Yes.

 

Link to datasheet

 

 

Iain

[OldGoldy]

 

 

 

If so how do I test it. I know its only supposed to let current flow in certain directions.

 

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

 

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.

 

Take a multi-Meter and switch it to Ohm x 1 or "diode -|<-"

 

Test between one of the "~" and "+" legs.

You should get either an almost-zero reading in one direction <600ohms, 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.

 

spec here:- http://www.datasheetcatalog.org/datasheet/diodes/ds21209.pdf

 

HTH

[alan_fincher]

Looks like a bridge rectifier to me.

 

I seem to recall that you can test it with an analogue multimeter on the Ohms setting but I could be wrong.

 

I think that you put one probe on the + or - terminal - the DC terminals - and the other on one of the other terminals - the AC terminals. You should see a needle deflection. You should get a reading with the probes one way round but not the other.

 

I think that's true to a point.....

 

that would be a partial test.

 

However a bridge rectifier is effectively 4 separate diodes joined a certain way, all in the one unit.

 

The test you have given would not I think identify a case where one of those diodes had gone open circuit for example.

 

The most reliable way, (if it passes that basic test), would then probably be to bung AC in, and look at the DC terminals with an oscilloscope - should look like this.....

 

 

EDIT:

 

Cross posted with Dave.

 

Haven't totally thought it through, but I feel sure he is correct on a method with doing it with no more than a multimeter - ignore my oscilloscope, then!

Edited April 27, 2010 by alan_fincher

[wrigglefingers]

It's not often I get to share this but I'd like to point out on behalf of all concertina players the world over (and at the risk of ever more well-deserved abuse) that the first bridge was invented by Samuel Hunter Christie and first effectively developed and used by Charles Wheatstone. Who went on to invent the concertina in 1829 as a pure tone generator ....

 

I'll get me coat ...

[mayalld]

It's not often I get to share this but I'd like to point out on behalf of all concertina players the world over (and at the risk of ever more well-deserved abuse)

 

Burn the witch!

[Biggles]

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

 

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.

 

Take a multi-Meter and switch it to Ohm x 1 or "diode -|<-"

 

Test between one of the "~" and "+" legs.

You should get either an almost-zero reading in one direction <600ohms, 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.

 

 

With the notch to the top right and referring to the data sheet I get the following readings in the diode mode:-

 

Neg prob on top left terminal red on the right = 1 Other way round = 436

 

Same result on the bottom pair but = 444

 

Red on bottom left black on top right = 967 other way round = 1

 

Red on bottom right black on top left - 1

 

Red on bottom right black on top right = 432 other way round =1

 

Red on bottom left Black top left 436 other way round = 1

 

Whats the verdict please.

 

Biggles

spec here:- http://www.datasheetcatalog.org/datasheet/diodes/ds21209.pdf

 

HTH

[wrigglefingers]

Burn the witch!

 

And there I was thinking kindly of you after this afternoon's contretemps with Phylis!

[RLWP]

There's lots of bridges in the Workington area that need rectifying

 

Richard

[OldGoldy]

With the notch to the top right and referring to the data sheet I get the following readings in the diode mode:-

 

Neg prob on top left terminal red on the right = 1 Other way round = 436

 

Same result on the bottom pair but = 444

 

Red on bottom left black on top right = 967 other way round = 1

This one confused me - not normally done!

 

Red on bottom right black on top left - 1

 

Red on bottom right black on top right = 432 other way round =1

 

Red on bottom left Black top left 436 other way round = 1

 

Whats the verdict please.

 

I'd say 'PASS', 'OK', 'NOT FRIED', but before returning to use try the '1 result' tests again with a higher range on the multi-meter,

just in case it may be 'leaky' - You should again get 1 or infinity readings.

 

Please do tell us where and why etc for your query, as this is a high(ish) voltage & current device.

[Tony Brooks]

Please do tell us where and why etc for your query, as this is a high(ish) voltage & current device.

 

 

Perhaps he thinks he has sorted a cheap GI

[WotEver]

I'd say 'PASS', 'OK', 'NOT FRIED',

Agreed. But it sounds like your meter either doesn't have a very low ohms range, or you didn't have it set to the lowest setting.

 

Whatever, it's doing the right things.

 

Tony

[carlt]

With the notch to the top right and referring to the data sheet I get the following readings in the diode mode:-

 

Neg prob on top left terminal red on the right = 1 Other way round = 436

 

Same result on the bottom pair but = 444

 

Red on bottom left black on top right = 967 other way round = 1

This one confused me - not normally done!

 

Red on bottom right black on top left - 1

 

Red on bottom right black on top right = 432 other way round =1

 

Red on bottom left Black top left 436 other way round = 1

In out, in out, and shake it all about

 

.

Edited April 28, 2010 by carlt

[Gibbo]

Sounds like the test was done on a very high resistance range. Otherwise the low number (1 in this case) would have been much higher and the higher number wouldn't have registered.

 

The reading that confused you is because that one is going through two diodes in series so it will have twice the voltage drop. It's normal.

 

All the readings indicate that it is working correctly. But remember that it's only a pretty basic test. It will however usually show up a dodgy one.

[Biggles]

Sounds like the test was done on a very high resistance range. Otherwise the low number (1 in this case) would have been much higher and the higher number wouldn't have registered.

 

The reading that confused you is because that one is going through two diodes in series so it will have twice the voltage drop. It's normal.

 

All the readings indicate that it is working correctly. But remember that it's only a pretty basic test. It will however usually show up a dodgy one.

 

 

The test was done with the Diode mode on the multimeter. I don't remember much from my brief stint in the electronics dept. on my apprenticeship some 30years ago, but my initial thoughts were the diodes were working OK.

 

How are you with 240v Generators Gibbo?

 

Biggles

[WotEver]

Sounds like the test was done on a very high resistance range.

Didn't I say that two posts previous?

 

Hey, I'm just sayin'

 

T

[JohnO]

A large bridge rectifier

[Gibbo]

The test was done with the Diode mode on the multimeter. I don't remember much from my brief stint in the electronics dept. on my apprenticeship some 30years ago, but my initial thoughts were the diodes were working OK.

 

Ah, then in that case it shows a completely different thing. It's nothing to do with resistance.

 

It shows the voltage drop across the diodes. The readings you got are all wrong. Unless it's just a cheapo meter.

 

The reading of 440 or so is wrong. It should be more like 0.55 - a cheap meter might do the test at too low a current which could show 0.44 but never 440.

 

The reading of 1 shouldn't even be there. It should show OL

 

How are you with 240v Generators Gibbo?

 

Not as good as some others on here.

[Iain_S]

(snip)

The reading of 1 shouldn't even be there. It should show OL

 

Some meters (mine included ) use 1 on its own to denote a high out of range reading.

 

Iain

[Gibbo]

Some meters (mine included ) use 1 on its own to denote a high out of range reading.

 

Iain

 

I did wonder that, hence the mention of "a cheap meter"

[OldGoldy]

Sounds like the test was done on a very high resistance range. Otherwise the low number (1 in this case) would have been much higher and the higher number wouldn't have registered.

 

The reading that confused you is because that one is going through two diodes in series so it will have twice the voltage drop. It's normal.

 

All the readings indicate that it is working correctly. But remember that it's only a pretty basic test. It will however usually show up a dodgy one.

Only briefly confused because I was expecting FOUR test results, not five.

 

'400ohms' or so is not an unreasonable reading for a silicon diode junction, but as long as all forward resistances are similar, then all should be OK.

 

My old (and notso cheap) Fluke meter shows infinity as a '1' - If the meter has a more detailed display then it may show a sleeping 8 ie infinity.

 

IIRC the diode/semiconductor range (where present) uses the higher voltage battery (9v, or 15v in an Avo) to ensure that the junction is forward biased to provide a current/reading. Or is the old grey matter failing me - it's along time since I worked with electronics and even then, it was in more of a practical rather than theory sense

[Gibbo]

Only briefly confused because I was expecting FOUR test results, not five.

 

'400ohms' or so is not an unreasonable reading for a silicon diode junction, but as long as all forward resistances are similar, then all should be OK.

 

My old (and notso cheap) Fluke meter shows infinity as a '1' - If the meter has a more detailed display then it may show a sleeping 8 ie infinity.

 

IIRC the diode/semiconductor range (where present) uses the higher voltage battery (9v, or 15v in an Avo) to ensure that the junction is forward biased to provide a current/reading. Or is the old grey matter failing me - it's along time since I worked with electronics and even then, it was in more of a practical rather than theory sense

 

Reread his recent post. The meter was on a diode check range. Digital meters (which this now appears to be) don't read in Ohms on a diode check range. They display the volt drop across the diode. Nothing to do with Ohms.

 

Analogue meters, on the diode check range, give a somewhat useless reading.

 

The other often confusing thing is that most analogue meters have the probe polarity the wrong way round on a diode check setting.

Edited April 28, 2010 by Gibbo

[WotEver]

The other often confusing thing is that most analogue meters have the probe polarity the wrong way round on a diode check setting.

Or indeed on the resistance ranges if I recall correctly. (Just recently replaced the 15v batt in my Avo 8)

 

Tony