[Amps] MOV - Varistor Reccomendations

[David Pruett]

Mike,

While this is not the question you asked, I'd point out that in a bridge 
rectifier, each diode (or string) has to stand off the peak AC input 
voltage during the half-cycle that it's not conducting, and this is not 
referenced to zero, but to the DC output voltage when used with a capacitor 
filter.

The 4800 volt AC input is around 6700 volts peak.  The filter capacitor is 
charged to this value, meanwhile on negative swings the rectifier has to 
stand off an equivalent negative peak.  You need about 13.4 KV worth of 
diode rating and you've got 8 KV.

I've run the power supply for my 40M 4-1000A amp off a 4800V pole pig with 
four K2AW 14-1 (14 KV rated) diode blocks.  Indicated plate voltage no-load 
is about 6600V.  My understanding is that the K2AW blocks are fourteen 
1N5408s in series.  The above analysis shows that I could probably use some 
design margin in this application, but it's run for more than a decade with 
no problems.

73,

Dave/K8CC


At 10:44 AM 1/29/2005, aborg wrote:
>Can anyone suggest what MOV to use for my 1N5408
>rectifier board. I an using 32 diodes , 8 per leg. My
>transformer is a 4800 Vac pole pig. I want to use the
>MOV's instead of the resistor/cap combo on each diode.
>
>=====
>Mike-KK4MS
>a_borg at yahoo.com
>
>
>
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