Re: From Member: using Digital Equipment Corp Transformers

dcassyc1 wrote:

> Hi All,
> I have a DEC power transformers which uses an oil filled capacitor on one of the windings, I suppose to provide Power Factor correction. The capacitor is missing and I don't know what value it should be.
> Is there a method I can use to determine the capacitor value?
> Is it possible to use this transformer without the capacitor?
>

This is a ferro-resonant transformer, similar to the Sola regulating
transformers. It will give horrible regulation without the capacitor,
so even a small load will cause the output voltage to collapse. The cap
has nothing to do with power factor correction.

I think if you put something like the rated load on the output, then you
can determine the correct cap by trial. If you have a Variac, you can
check the regulation, when the cap is right, the output voltage will be
roughly stable while input voltage varies +/- 15% or more from nominal.

One disadvantage as a CNC power supply is that these transformers have
no surge capability. Above rated load, the output voltage and current
drop steeply. A conventional transformer can deliver several times
rated load for short surges in power when motors are accelerating.

Jon