[Boatanchors] Are 400 Hz variac's good for anything but a real 'boat anchor'

[Bruce Long]

Everyone is entitled to their own opinion. 
No one is entitled to their own facts.

I have stated a 400 Hz 120vrms variac connected to 120vrms will self destruct.  Everyone agrees with this. Indeed this was the reason the thread was created.

I have also stated the guys suggesting the same variac can be used at 60 Hz if the voltage is limited to about 18 vrms are correct and have offered an algebraic explanation why this is so.

With respect, which part of my "opinion" is incorrect and why?  

--- On Mon, 7/18/11, J. Forster <jfor at quik.com> wrote:

From: J. Forster <jfor at quik.com>
Subject: Re: [Boatanchors] Are 400 Hz variac's good for anything but a real           'boat anchor'
To: "Bruce Long" <coolbrucelong at yahoo.com>
Cc: "Bill L''Fuqua" <wlfuqu00 at uky.edu>, doc at kd4e.com, "John Hurst" <hurstjsj at verizon.net>, "'Boatanchors List'" <boatanchors at puck.nether.net>
Date: Monday, July 18, 2011, 11:17 AM

You are entitled to your opinion.

-John

================

> Agreed
> But the 7:1 guys are correct  Nowhere in the thread has anyone suggested
> applying 120vrms/60Hz to a 400 Hz variac.  The 7:1 factor is the required
> de-rating needed to operated a 400 Hz variac on 60 Hz in order to avoid
> core saturation.
>
>
>
> --- On Mon, 7/18/11, J. Forster <jfor at quik.com> wrote:
>
> From: J. Forster <jfor at quik.com>
> Subject: Re: [Boatanchors] Are 400 Hz variac's good for anything but a
> real      'boat anchor'
> To: "Bruce Long" <coolbrucelong at yahoo.com>
> Cc: "Bill L''Fuqua" <wlfuqu00 at uky.edu>, doc at kd4e.com, "John Hurst"
> <hurstjsj at verizon.net>, "'Boatanchors List'" <boatanchors at puck.nether.net>
> Date: Monday, July 18, 2011, 10:58 AM
>
> The statement is true. In a properly designed 400 Hz transformer operating
> at the rated voltage, the iron is not being saturated during any part of
> the cycle.
>
> If you go to 60 Hz with the same applied voltage, the iron will be
> hopelessly saturated, and it's incremental permeability will drop to near
> that of free space. It's like the iron just vanished.
>
> The magnetizing current will go up far, far more tha 7x.
>
> Best,
>
> -John
>
> =================
>
>
>> "The magnetizing current @60 Hz will *much* higher than 7 times the
>> current
>> at 400Hz."
>>
>> Please explain- justify.
>>
>> I agree with the 7:1 guys on this. 
>>
>> Basically the issue arises in the electronic speed/torque control of
>> induction motors.    Bruce   KJ3Z
>>
>
>
>