Re: Soft transformer turn on without a variac

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

Original poster: "Bart Andeson by way of Terry Fritz <teslalist-at-qwest-dot-net>" <classi6-at-classictesla-dot-com>

Hi Peter,

I guess there are many things you could do. If you are looking for a one 
switch setup (power on does it all = power off does it all), You could 
simply tie the "power on" to a relay to energize the motor. That would take 
care of step 1.

Step 2 would be the soft start for the variac. You could rig a very simple 
RC delay to turn on a transistor when the RC voltage reaches the base 
turn-on value giving the motor time to reach rpm. The power would come from 
the power on switch. Simple half bridge for DC to charge the RC. The 
transistor would then turn on a DC coil relay and energize AC to the 
variac. But, this still isn't a soft start. A dampening resistor inline 
with the variac (say about 2 ohms) would be a cheap. Or you could get 
tricky and throw a slow geared-down motor onto the variac shaft and limit 
switch where to stop at "on" and "off". As fun as that would be, a 
dampening resistor is probably all you need. The power off would take care 
of itself.

Take care,
Bart

Tesla list wrote:

>Original poster: "Peter Terren by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <pterren-at-iinet-dot-net.au>
>
>Hi all.
>For my 5 kW museum coil, 
><http://members.iinet-dot-net.au/~pterren/Scitech.htm>http://members.iinet-dot-net.au/~pterren/Scitech.htm 
>,   I need to have a single switch for turn on preferably without a variac 
>to keep things simple for the staff.  The present system has solid state 
>relays but is complicated and unreliable. I need to turn on the motor 
>first then a couple of seconds later soft turn on the power to the 
>transformer. Even switching  on power to a normal variac gives a spike 
>that will trip my lower current breakers. The whole system will have to be 
>electrically quiet.  Does anyone have experience with inrush limiters or 
>have other suggestions?
>
>Cheers
>Peter (Tesla Downunder)
>