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Posted by on March 13, 2007, 4:25 am
On 12 Mar 2007 12:36:46 -0700, ls1mike@gmail.com wrote:
>I'm tweaking an old coffee roaster using a variac. Originally, I used
>it simply to compensate for variations in the line voltage at a
>particular power outlet, but I have since started to deliberately
>adjust the voltage up or down to control the temperature, usually in a
>range between 110-135 VAC. Essentially, the roaster is nothing more
>than a hot air popcorn popper with a motor driven fan and a heating
>coil. I was wondering - if I increase the voltage by, say, 10%, how
>does that affect the power consumption? Since the coil gets hotter,
>it's clear that it's consuming more watts. Would total watts also
>increase by 10%, or does the efficiency of the heater coil change?
>The motor speed changes with the voltage, as well. If watts increase
>at a faster rate than voltage, then, at some point, I will probably
>trip the breaker (although the heater coil probably would have already
>failed). In general, how tolerant are heater coils and electric
>motors to higher voltages?
As others have said it is a squared function. What you should really
be asking is your variac big enough to handle the wattage that you
are attempting to control. Not all variacs are large capacity.
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