Re: [tesla] Soft transformer turn on without a variac

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Original poster: "Black Moon by way of Terry Fritz <teslalist-at-qwest-dot-net>" <black_moons-at-hotmail-dot-com>

Well, I was thinking a complex triac startup
Depends on the load, this is mainly for with a large rectifyed cap on the 
output
Now, as you know, at the peak of the ac wave, theres 0 flux in the 
transformer and 0 'current' (assumeing no load)
So, if we turnon during the peak, we get 0 'transformer' inrush over the 
next few cycles
Unfortualy, this causes alot of cap inrush
Now, extending this, theres a point during the peak of the ac waveform when 
a traic can turn off (more during the riseing edge if the transformer is 
loaded) as the current reverses
So what I think, is if we turned the triac on at say 340, then off at 20, 
then on at 320, then off at 40, (degrees phase... well, I guess you'd have 
to devide by 2 and do the same for the other half of the ac wave but you 
get my idea) we could gradualy charge the cap to limit the cap inrush, and 
still have (near) no hv spikes from the transformer from disconnecting it 
while theres flux in the core (the load should snub any flux in the core if 
there is a load, and if not, it won't turnoff till the peak anyhow when 
there is no flux)
With this soft triac turnon, the flux in the transformer would never go 
over the normal conditions, and the cap inrush would probley be lower then 
your TC's rms :P (and you could fully adjust the cap softstart time)
Of course, if your cap inrush isent a problem, then you can just turnon at 
the peak. (Note. you'd have to find some way to keep the spark gap from 
triggering while 'softstarting' the caps anyway, or softstart below the 
triggering voltage, then 'jump' to full on operation)


>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Re: [tesla] Soft transformer turn on without a variac
>Date: Mon, 28 Jul 2003 06:23:19 -0600
>
>Original poster: "Peter Terren by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <pterren-at-iinet-dot-net.au>
>
>Hi all
>Thanks for everyone's comments. The solutions have varied from triacs
>through resistors to valves. I am not inclined to use triacs as they have
>blown in the current set-up (as solid state 40A zero crossing relays).
>Valves are beyond my expertise. Resistors will diminish the problem but will
>still give some transients with mechanical switching. I have however
>(finally) located an Australian distributor of  inrush limiters (negative
>temp coefficient thermistors) up to 30A with 0.5 ohm cool and 0.01 ohm hot
>(65 C) resistance.  Several of these in series would drop surge currents in
>a 30A system significantly with only a volt or two drop across each when
>running.  Unfortunately I don't see how I can parallel them unless thermally
>linked with series resistors or inductors to balance the load. (See
>http://international2.farnell-dot-com/Search/search-frame.jhtml enter 606832
>into search.).  I suspect that they may work best in an SRSG set-up where
>maximum current is relatively stable. I will post my results when it is
>running.
>
>Cheers
>Peter (Tesla Downunder) http://members.iinet-dot-net.au/~pterren/
>
>----- Original Message -----
>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Monday, July 28, 2003 2:58 PM
>Subject: Re: [tesla] Soft transformer turn on without a variac
>
>
> > Original poster: "Black Moon by way of Terry Fritz <teslalist-at-qwest-dot-net>"
><black_moons-at-hotmail-dot-com>
> > What about a triac soulution? iv been thinking about soft start poweron
> > devices that might be even able to have soft off (no hv surges)
> > If anyone wants to hear more just ask.
> >