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Failure modes of bridge rectifiers. What can they handle?

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fastline

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Long story short, I was working on an audio amplifier. I found the problem, insulation film isolating 6 mosfets from the case/ground was contaminated and 2 were basically bypassing the gate and were WFO. I tested the circuit with the speaker hooked up which emitted a very loud hum. I only switched the amp on 3 times for less than 1 sec but just not sure what kind of power it tried to pull during that time.

I got the problems worked out in the circuit and system was running fine until I went to add some coal to the fire and the full wave bridge rectifier shorted from + to AC and popped the main fuse. I was curious if a bridge can degrade from surges or if they are just good or bad? Do they typically fail shorted? I was also a bit concerned of any damage down the line from the short but This is at the very front of the circuit and things are testing good so far.
 
Hi,

Bridge rectifiers are made from 4 diodes. Diodes fail either short or open. If they short you will see the fuse blow, and open the device wont work.
You can measure the resistance of the individual diodes with a meter and see which one is shorted, if any, or which one is open, if any.
 
oh, I already know it is shorted per my diode tester but I guess I have never seen a diode blow when it was not immediately exposed to out of range conditions. Ie, when it blew up, it was not any where close to it's rated capacity BUT it may have seen a few hard pulls over it's rating when the amp was shorted. I did have the bridge out at that time and it diode tester perfect. There is also a possibility that there is excessive current draw in the amp but there are no signs of that and it runs like a top.
 
The diodes in the bridge may have been stressed a bit via overheating when the output devices were shorted. And they will still test fine but the lifespan of them may very well have been shortened due to running hot when the output devices shorted.

If everything is running fine now and the bridge rec and output devices aren't running hotter than they should be then you should be out of the woods on this.
 
Well, it certainly is not running right now until I get another bridge but I did pull it down the second it blew and the bridge was far from hot. I cannot help but think the desoldering it a few times and zapping it with maybe a little more than rating for a second or so might have damaged it. I hope that is the case. I plan to get another bridge and give it another shot..
 
Ah OK...I was under the impression that you had already replaced the bridge. Let us know how everything works out!
 
Well, it certainly is not running right now until I get another bridge but I did pull it down the second it blew and the bridge was far from hot. I cannot help but think the desoldering it a few times and zapping it with maybe a little more than rating for a second or so might have damaged it. I hope that is the case. I plan to get another bridge and give it another shot..

Are you you still working on that amplifier, cause you made like 30 threads on it!
 
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