Re: Variac current and VA rating

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Shaun Epp by way of Terry Fritz <twftesla-at-qwest-dot-net>" <scepp-at-mts-dot-net>

I agree mostly.  If three amps is drawn from 120VAC then 3A flows from the
input to the common return. Also nine amps flows out the the brush TAP point
and returns via the common return.

So that means that the currents either adds or subtracts (input and output)
in the variac between the tap point and the common return.  Also since it is
a continuous coil being mutually induced by the windings, the current in the
section between the tap and common should be gradient (each turn of wire is
a transformer with induced currents and voltages in it adding up).

Shaun,

 sorry Pete for the delays  and I'm still not sure if they add or subract.
I assume that one could put an ammeter between the common return of the
variac and source return and load return.  View the current with no load
attached and that with the load.  A good sample load could be a heater
element...( kettle, coffee maker heater, etc...)

-----Original Message-----
From: Tesla list <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Friday, June 01, 2001 7:14 PM
Subject: RE: Variac current and VA rating


>Original poster: "Ray Haynes by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<ray.haynes-at-home-dot-com>
>
>If you are pulling 9A from the brush output then 9A is flowing from the 0V
>end terminal to the brush. The only real magic is that it won't necessarly
>take 9A in to produces that 9A out, that depends on the voltage setting.
The
>input to output current is inverserly propotional to the input to output
>voltage just like a regular transfomer (Vin/Vout = Iout/Iin).
>So your example of 120VAC/40VAC = 9A/3A is correct. If we look at the
>current flowing in the windings we would see 3A in the wire from the 120VAC
>connection to the point where the brush is touching and 9A from that point
>to the 0VAC connection (for a setting of 40VAC out).
>
>Hope that helps,
>Ray
>
>
>> -----Original Message-----
>> From: Tesla list [mailto:tesla-at-pupman-dot-com]
>> Sent: Thursday, May 31, 2001 11:55 AM
>> To: tesla-at-pupman-dot-com
>> Subject: RE: Variac current and VA rating
>>
>>
>> Original poster: "Pete Komen by way of Terry Fritz
>> <twftesla-at-qwest-dot-net>" <pkomen-at-zianet-dot-com>
>>
>> Hello Shaun,
>>
>
>***SNIP***
>> For Mark,
>>
>> I was aware that some people run variacs over the rated VA.  I
>> don't need to
>> do that yet.  I have a 20 amp 140vac output variac also.  The
>> basic question
>> is: for a variac input of 120vac at 3 amps and an output of 40vac
>> at 9 amps
>> (ignoring losses), what is the current in the windings between
>> the 0vac and
>> 40vac points?
>>
>> Regards,
>>
>> Pete
>>
>>
>***SNIP***
>