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Re: herbach and redman
From: Jim Lux[SMTP:jimlux-at-earthlink-dot-net]
Sent: Tuesday, November 25, 1997 10:35 AM
To: Tesla List
Subject: Re: herbach and redman
> I figured that since these transformers require a 10 uf cap connected to
> a winding that is neither primary or secondary that they must need to
> resonate to get the 5kv. Disconnecting the cap dropped the output a lot.
> I guessed that the capacitance of my coil threw the resonance way off and
> it just didn't work. I later band sawed the windings off the cores and re
> wound my own windings. I got rid of the magnetic shunts too. Now I have 2
> transformers that work very well.
> recently I got the idea that maybe someone should try removing
> the 10uf cap and apply AC power to this resonating winding and see what
> happens. I faintly recall measuring the voltage on this winding in
> operation and it was at 400v or so a step up transformer might be needed
> here.Use ballasting to be safe.
I assume that these transformers are similar to the General Electric 4500
V, 400 mA units sold by C&H Sales in CA. The weight, size, and price seem
right. The third winding is nominally 600 Volts, and is used to connect a
power factor correction capacitor. The transformer was designed to run a
discharge lamp in a copier, so it has a lot of leakage inductance to limit
the current (like a neon sign transformer). Unlike a NST at a lowly 400 VA
or so, this unit is around a kVA, and having a bad power factor causes all
kinds of trouble, particularly in office buildings where they use 3 phase Y
connected power (208/120) with a small neutral conductor. Therefore, they
add the 10 uF cap to correct the inductive component. It is cheaper to use
a 660VAC 10 uF cap on the tertiary winding rather than put a much larger
one on the 110V primary (it would have to be about 300 uF, pretty
expensive). 660VAC is a standard voltage for motor capacitors, etc.
By the way, the presence of the tertiary winding means that you can do a
cascade set up, feeding the 600 Volts from one transformer into the 600
volt winding of another transformer and series connecting the secondaries
to produce a 9kV, 250 mA transformer with the core of the second
transformer floating at 4500 Volts. Two such cascades (4 total
transformers) with the bottom ends grounded makes what is effectively a 250
mA, 18 kV current limited neon sign transformer.
It will weigh about 200 lbs, so you should probably do as I did, and mount
it on a steel hand truck or some reasonable casters. I use mine to make big
jacob's ladder type displays and to pull arcs for special effects purposes,
as well as a general purpose HV power supply with a variac and a HV bridge
rectifier.
I haven't tried removing the shunts on these yet, but I have done extensive
measurements on the leakage inductance, and other parameters. I'll post
them as soon as I finish writing it up.