[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: purpose of a variac?
Original poster: <dgoodfellow@xxxxxxxxxxxxxx>
It depends on how you define optimized performance. I think my coils
are at their best when the spark gap is set conservatively, and the
spark output is very continuous and flowing. The coil sounds smooth
like a saw cutting steadily. When the gap is set this way, I see
activity at the spark gap even when the variac is only at 20% of max.
There may be no breakout from the topload at this level of input, but
the transformer clearly has enough voltage to start arcing across the
gap. In my last coil (ebay# 6226319288 ) The spark gap (made from
3/8" tungsten electrodes) was set at 13/64" (.203") for the spark
photos. I have a paper that was written by Mark S. Rzeszotarski PhD.
that defined a coil using the same gap electrodes, operating at
.200". In this paper, the breakdown voltage is 17.6 kv. Remember, I
am using a 9kv 60 ma transformer, with LTR caps, and according to
this paper, the gap is firing at nearly double the transformer voltage.
If I run a TC with the gap open wider than .200" the sparks are not,
to me, as pleasing to the eye. The variac will have to be turned to
1/2 to 3/4 of it's full output before the gap fires. The sparks off
the topload are less continuous, and one can hear the slower bang
rate as the caps can not cycle as quickly as they did with the gap
set closer. This state of operation "feels" to me, that the coil is
running at the brink of destruction.
If anyone has different views about the breakdown voltage at
.200" I would like to hear what you have to say.
----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
Sent: Sunday, January 22, 2006 9:19 PM
Subject: purpose of a variac?
Original poster: "Qndre Qndre" <qndre_encrypt@xxxxxxxxxxx>
I've read several documents on the internet which claim that the
power throughput of a TC can be adjusted using a variable
transformer to power the supply transformer of the coil. I don't see
how this could be done under regular circumstances. If the input
voltage of the supply transformer is reduced, it's output voltage
reduces as well. The voltage across the capacitors can never exceed
the supply voltage (unless you use resonant charging which may
destroy the secondary winding of your supply transformer). Since the
spark gap in the tank circuit is best to be tuned just to fire at
the absolute voltage peak for optimized performance it will never
fire with reduced input voltage to the primary circuit.