AVR relays - how do they work?

[aroby]

I have an APC UPS which is showing a fault that apparently is due to an "AVR Relay Weld".  I opened it up and sure enough there are 4 Omron relays on the board (soldered in, even though these relays can be socketed!).  I guess my only option for fixing it is to take the board out and figure out which relays are at fault.  I assume from the problem description that they are either shorted or won't activate.

But my question is what are they for?  As I understand it, AVR is about voltage regulation, so I'm not clear what relays do in that respect.  And if they weld together, why would that happen?

Thanks for any insight!

Anthony

[krish2487]

The way a AVR worksis to switch between different taps on the transformer to boost or buck the incoming AC mains to provide a nearly constant output voltage (gross oversimplification, but for this purpose it should suffice). Quite useful in areas where the line voltage is not constant nor consistent.

What I understand from what you posted, it seems two relays have gone bad effectively shorting tap(s). Their going open, generally, should not cause any problem - but it is dependant on the circuit.

Checking which relays have gone bad and replacing them should solve the issue.


There might yet be another cause, the drive for the relay coil - either the drive transistor or the microcontroller pin (I am assuming there is a microcontroller inside) have gone released the magic smoke and have caused the relay to permanently latch.
 

[aroby]

Thanks for the explanation - I think I get it.  I don't see any damaged components so hopefully replacing the relays will get this going.  Surprisingly, the only place I have found that has them is in China!  Maybe since the boards are made there Omron only sells them there.