Re: Variac turn-on surge solution

• To: tesla-at-pupman-dot-com
• Subject: Re: Variac turn-on surge solution
• From: Neon John <johngd-at-bellsouth-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Sat, 30 Oct 1999 08:02:22 -0600
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Tesla List wrote:

> 
> Hopefully this info will help you out.  I bet with low resistance wiring
> those spikes my be getting higher than my 100 amps spikes.

You're right.  I have the same problem with my neon bombarder.  The
pig is fed with a 25 amp variac operating as a variable choke in
series with a fixed choke.  Even with the pig's primary open,
hitting the contactor with the variac set anywhere much above 50%
will thump the 60 amp breaker feeding my bench.  I solved the
problem with a soft start circuit.  This involves nothing more than
a 10 ohm, 100 watt resistor in series with everything, shorted by a
time delay relay.  This relay is very simple - a DC coil relay
shunted by an electrolytic cap and fed through a resistor, values
selected to delay the closing of the relay by about half a second. 
This relay is driven through a small bridge rectifier from the main
contactor.  When I hit the loud switch, the main contactor
energizes, feeding power through the resistor.  A half second or so
later, the resistor is shorted and the system is at full power.  I
have a 12 volt, 250 amp DC power supply with about a farad of filter
caps that uses the same soft-start circuit.

John

-- 
John De Armond
johngdSPAMNOT-at-bellsouth-dot-net
http://neonjohn.4mg-dot-com
Neon John's Custom Neon
Cleveland, TN
"Bendin' Glass 'n Passin' Gas"

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