Re: Current regulation for Variac

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Tesla by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<tesla-at-tezla-dot-com>
> 
> Hi all.
> 
> I have a small question about variacs. I have a 3,5kVA variac(Uin=230V).
> When i bring it online it sometimes(about 1/3 of the times) it draws so much
> current from the mains that my 10A fuse blows although i don't have any load,
> except the variac itself.
> Is there some way to correct the powerdrain with say a choke or something to
> make it "turn on" smooth? This problem is really annoying.
> Thought i hear with you guys first.
> Any help is appreciated.

	Put a resistor (few ohms) in series with the variac and short it after
applying power.  The variac has a very low DC resistance and, depending
on the turnon phase with respect to peak line voltage, there can be a
large DC component of the input current which can cause the problem. 
This is always a problem with big inductive devices connect to power
line with limited current capability.

Ed