-----Original Message-----
From: Joe Crawford
I knew a guy who used a 30 amp variac to feed a 5 volt, 30 amp filament
transformer on his quad driven element.Worked real good to melt the ice.
Joe W4AAB
Joe,
This is a great idea but the variac can be much smaller. The current needed
is reduced by the turns ratio of that filament transformer. If the primary
is 120 vac, then the turns ratio is 120/5 or 24. Therefore, if we take the
30 amps and divide that by 24 we get 1.25 amperes. The variac only needs to
be rated for a little over one ampere. I might be tempted to use a light
bulb in series with that transformer primary where the current to the load
will vary by the bulb wattage rating, and the load resistance. Remember that
the resistance of the bulb is very non linear where the cold filament has a
much lower resistance than a hot filament. So I'd start with a 100 watt bulb
and see if that works. I would not go over 150 watts with the bulb rating
though. Having a clamp on AC current probe would be handy in a case like
this.
I picked another solution to the ice storms. Back in 1976 I moved to central
Texas. Getting any ice or snow here is pretty rare. ;-)
Regards,
Jim
WD5JKO
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