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

J. Forster jfor at quik.com
Sun Jul 17 13:05:02 EDT 2011

```> I am math-challenged, or more precisely, algebra-challenged.
>
> Are you saying that a 400Hz device operating at 60Hz has

The allowable input voltage has to be decreased by 60/400.

> So if he stayed with 120vac and the device was rated 65A @ 400Hz
> it would be good for 10A @ 60Hz?

The current rating stays the same as for 400 Hz and 60 Hz. The max
allowable current is determined by the wire size, not the core.

> So one rated at 10a @ 400Hz would be good for ??? @ 60Hz?

10 A @ (60/400)*120 V at 60 Hzs.

> I am interested because I have a pair of selsyns/synchros that are
> rated at 400Hz and finally have a purpose where I can see if they
> are functioning correctly and can handle a little torque (turning
> a big roller inductor).

You can apply 60/400 of the allowable 400 Hz voltages at 60 Hz.

A big rollerductor is likely to need more torque than a selsyn can supply.

-John

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

>> The issue is core saturation. If you run it at a lower input voltage, 18
>> V
>> or so you can still run it at 10 amps out. It's still not too useful,
>> but
>> you could use it with a transformer for a variable filament supply or
>> low
>> voltage power supply.
>>
>> 60/400*120V = 18V
>>
>> John,KU6X

```