----- Original Message -----
From: "John Irwin" <crazytvjohn@yahoo.com>
I assume you mean the current drawn by the primary? If so it is simple ohms law. In a transformer, wattage in equals wattage out plus the losses. I'd say assume at least 5% or maybe 10% loss. 10 Vac X 20 amperes = 200 watts x 1.05 = 210 watts so you would have 210 watts being drawn out of the line. For 10% loss it would be 220 watts. Then convert watts to current.

Best,

Will


To: amps@contesting.com
Subject: [Amps] filament transformer
Date: Thu, 7 Jul 2005 17:54:00 -0700 (PDT)

> 
> hi
> I have a transformer 10vac at 20 amps.  110vac primary.
> 
> Does anyone know how to calculate the primary ac line draw.  I want 
> to use a variac to put it on the money .  Need to get the right 
> auto transformer.
> 
> thanks
> john kb9tc
> 
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