Re: Does a variac with no load dissipate power?

["Bert Hickman" <bert.hickman-at-aquila-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Gavin,

Once you get past the magnetizing transient, very little (probably less
than 3% of the variacs' rated current). However, the initial current
transient when power is initially applied to the variac can be very
large unless you limit it with a low-valued resistance that you later
"short out". I have a 28A variac that regulalry trips a 30A breaker when
first powered up (with NO load). 

-- Bert --

Tesla list wrote:
> 
> Original poster: ghub005-at-xtra.co.nz
> 
> Hello list
> 
> I feel a bit embarrased about asking this, but does a variac with no
> load consume a signnificant amout of power? I imagine it dissipates
> a little power through hysteresis + resistance etc - but I have no idea
> of the actual amount.
> 
> I'm asking because I've just finished my 11kVA three-phase PSU
> and I want to put a switch in that allows me to bypass the internal
> variac and inductive ballasts. The circuit I have in mind won't isolate
> the variac stack - it just switches between the variacs' output
> terminals and a bypass line.
> 
> Thanks in advance for your help,
> 
> Gavin Hubbard

-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-com
Web Site: http://www.teslamania-dot-com