Re: Power supply softstarts

I asked a lecturer in electrical enginnering about this, despite
being a lecturer he is very practical ;)

"I KVA is about 4 amps. A big supplly current. Toroidal transformers
have an excellent efficiency due to having no small air gaps in their
magnetic circuit. Unfortunately this means that they can retain flux
on swiths off of the supply. If they are switched on at voltage zero
such that the rate of change of flux required causes the transformer
flux to grow in the same direction as the residual flux then
saturation quickly occurs as the flux is offset by the residual
value. The only current limit is then the resistance of the primary
winding and the very low leakage reactance. Hence bang. 1KVA should
not be enough to blow the fuse though normally.

The very big capacitor with no current limit on the input will
compound the problem of current surge as again there is little to
limit the current.

The simplest solution would be additional primary resistance on a
timer as Ron (enother chap I asked) says."

So I will go for some form of power resiter on the primary, shorted
by some means after some time. No need for ebay parts, I have a
budget :P

Cheers,

Graham