[R-390] Variacs and solas: last thoughts.

[James M. Walker]

Well before the thread goes away,
FWIW. I use variacs in the shack, for various rigs and as test devices.
I also on occasion repair them at the University, where they are used in
abundance. A while back I got a bunch of info about the PROPER use of
the
devices and also some safety info.

I have big rigs that run on 115 VAC and draw close to 30 amps in some
cases, less in others. Things I have noted is that you need to maintain
the proper wiring per NEC and there is usually not a problem with them.
One problem most folks miss is the neutral and hot lines in power
distri-
bution, and whether or not there is a ground to the variac from the main
circuit breaker. It matters, and can present safety problems, along with
voltage instability.

Ken I bet if you check your line back to the breaker box you find the
Hot
(black) lead is reversed to your variac, that pops the breaker. I never
assume that the lines in a house are correct, I always check that the
lines
go where they should, I have seen as mush as 60 VAC chassis to chassis
in
units that had the hot and neutral lines reversed to the units. That was
with the units turned off, and is NOT a good thing.

I also have a broadcast transmitter that uses 220 VAC and a homebrew KW
that uses 230 VAC (refurbed pole pig) for the ac input, I run them each
on a separate 0 - 240 VAC variac, they have a 40 amp rating at 240 VAC.
I haven't had any heating problems or circuit breaker problems ever. As
for fusing, I put circuit breakers two pole type to the input of the big
variacs and fuses in the input to the 10 amp variety, for 20 amps and
larger I use the fuse cartridge type FN those are about 2 inches long
and
3/8 inch in diameter. The units that have a built-in variac also have
a metering socket that measures the output volts of the variac. The
others
all have verified ac voltmeters across the output with a socket for
checking
accuracy.

Variacs are ok for use as long as they are used properly, they work well
and save a lot of headaches later on. Just my 2 centavos!
Jim
WB2FCN


"Kenneth G. Gordon" wrote:
> 
> The Variacs I have seen and used can ALL be wired so that the output
> is both higher (140VAC) and lower (110 VAC) than the input voltage
> (120 VAC), but all such "adjustments" are internal. The Variac has to be
> partially dismantled in order to do the changes.
> 
> I have several Variacs which have two-sided dial plates: one side reads
> from 0 - 100 PERCENT, and the other side reads 0 - 140 VOLTS, so
> you flip it over to the side you want.
> 
> I also have one large Variac that has such low impedance that when I
> turn it on,  the breaker feeding that socket blows. Sometimes it takes
> multiple attempts until I hit it at a valley in the sine wave. Then I leave it
> on. I haven't turned it off for about the past 5 years.
> 
> None of mine are fused in the output, but I think they will become so
> shortly.
> 
> Ken W7EKB
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