[AMRadio] Re: ICE STORM


Joe Crawford crawfish at surfmore.net
Sun Mar 9 09:40:28 EST 2008


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" <jcandela at prodigy.net>
To: <amradio at mailman.qth.net>
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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