I realize that one could use one smaller, but if you got a 30 amp on hand,
crank it up. I have been doing this electronics thing for 35+ years, so
familiar with turns ratio, etc.It is good to have things like variacs, like
the one I got from WA2RQY recently. Nice to put in 0-140 and get out 0-260
VAC!!
Joe W4AAB
----- Original Message -----
From: "Jim Candela" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Sunday, March 09, 2008 8:56 AM
Subject: [AMRadio] Re: ICE STORM
-----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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