Variac

[J Forster]

Bob Groh WA2CKY wrote:

> Three comments here:
> 1.  Placing a fuse in series with the capacitor implies connecting the fuse in a high voltage dc circuit and that would, at a minimum, require a special kind of fuse - one rated for the appropriate dc voltage and capable of handling the required fault current. Breaking a DC circuit (more than 30 VDC or so) requires special arc quenching mechanisms. Not always easy or desirable.

I certainly never suggested that.

> 2.  As someone else noted, a fuse in the transformer primary circuit will achieve the same purposes.

Agreed.

> 3.  In any event, a failing  capacitor might not cleanly fail in a 'shorted' condition but might simply go to a low impedance state (i.e. pull extra current) which will not necessarily blow a fuse but will, given enough time, fry the transformer.  Again don't ask how I know this but I have a fried transformer to prove it happens!

Generally, a HV cap in a BA will not last long in such a state. It will either reform itself or fail short. In the latter case you will loose the primary fuse (assuming the value is right) and / or the rectifier tube. Neither is usually catastrophic. IF you put a 30A fuse in the primary, you deserve to loose the transformer!

Best,
-John

>
>
> Bob Groh

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