MOVs and surge protection/transient absorption

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WBear2GCR:
Thought I'd mention that I've read that MOVs will not provide protection after an initial "hit"! Apparently they change characteristics once they are "hit", moving the threshold voltage substantially or making them not work properly at all.

The information I've read says that in practice a large inductor and suitable shunt capacitors will provide superior performance compared to a MOV - it's just that the inductor is way bigger, so it is not a popular method.

For whole shack protection, it seems to me that the inductor method is a pretty good idea...

Seems to me that it is possible that a large iso transformer would likely be sufficient,  due to the large self inductance, although I'm not certain of that. The resources I've read have indicated series inductors on both sides of the line work better than 99% of all other transient suppresion devices and methods.

So, FYI, don't count on those MOVs to provide long term protection, since once they take a good "hit" apparently they go south - and there is no external indication that the performance has been degraded.

           _-_-WBear2GCR

WA1GFZ:
I have a box full of dead Cubic R3030 power supplies and a number of them have failed due to MOVs. When one of them fails the bridge rectifiier gets fried and sometimes takes out the circuit board.

K1DEU:
I do not suggest using a MOV for Power Transformer protection. 

With the Transorb and MOV in parallel the slow MOV only keeps the transorb from shorting in a good blow. Therefore we do not have to unsolder the transorb that shorted in a picosecond or faster and saved the transformer magnet wire!

Yes we do have to reset the circuit breaker or change the fuse towards the Mains.

These two devices in parallel have been proven many times!

Reference my recent post  http://amfone.net/Amforum/index.php?topic=12685.msg98426#msg98426

John K1DEU

WBear2GCR:
yeah John, but my point is that after even one hit the MOV is basically useless and there is no way to tell if it still is working without removing and testing its parameters. That's the problem with them... it's unclear to me if the MOV ever gets to do anything if the Transorb fires first? Since both are voltage threshold devices, if the Transorb fires, it pulls the voltage down before the MOV gets to "see" sufficient voltage to fire. Which does make the MOV a sort of back-up I guess.  ::)

And, if it for your shack, then the inductor solution on the mains obviates all that stuff... ;D

            _-_-bear

WQ9E:
There is some useful information on ICE's webpage:  http://www.iceradioproducts.com/10.html

By the way, since installing ICE suppression devices at the service entrances for my house, barn, and garages I have had no damage to anything in over 10 years.  Prior to that I had several "incidents" in my rural and lightning prone location and lost on separate occasions a well pump, several security lights, phones and computers.  The only negative issue is a bit more flickering during thunderstorms and you can also hear the suppressor box humming a bit from the high pressure sodium lights and also when the backup generator is in operation, probably the noise is from the inductor in the RFI network.

Rodger WQ9E

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