Roger
Did those SCRs have an L/C filter out to the mains? I fit a MOV directly
across the SCR or Triac.
David
G3UNA
> On 11/25/2010 2:14 PM, David Cutter wrote:
>> It is my experience that MOVs should not be placed directly across the
>> mains; they should have some limiting impedance, just like zeners do in a
>> dc circuit. I always fit them downstream of the mains filter so that as
>> they conduct there is a limiting Z for the period of the glitch. They
>> are not meant to be sacrificial but they would be if placed directly
>> across the mains with essentially extremely low source resistance.
> MOVs should be installed down stream of fuses or breakers.
> I should have said no flammable objects should be placed close to them.
> Carl is correct, MOVs don't normally catch fire, but a shorted one can get
> very hot, or even explode. I've seen a pair of #6 wires sticking straight
> out from where a 50,000 joule MOV "used to be" and I've also been in the
> next "cage" over from one when if blew. It takes a lot of power to explode
> a 50,000 joule MOV and the results are spectacular. The idea was to
> protect a pair of 1200 Amp SCRs (bout the size of a hockey puck and water
> cooled) from spikes, which they sometimes did. <:-)) The fuse they'd take
> out was pretty spectacular for size too.
>
> All in all even if the SCRs went they were still worth the investment.
>
> 73
>
> Roger (K8RI)
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|