Re: Transformer Soft Start

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Keith Bowers <kabowers@N...>
wrote:

> On Thursday 03 July 2003 13:56, wanliker@a... wrote:
> > In a message dated 7/3/2003 11:29:22 AM Mountain Daylight Time,
> >
> > tiffyted@l... writes:
> > > The transformer is 230v only primary and 2 x 40v 12.5A secondary
> >
> > You can always open all leads, then apply about 6 VAC to one of

the

> > secondaries to check out the transformer, and to help phase the

primaries,

> > and the other secondary, if they are not marked.
> > bill
> >
> >snip<
> Then leave the secondaries unconnected and connect just the primary

to the AC

> supply and see if you still have a large inrush current. Next

connect the

> secondaries and try. Then add the rectifier(s). Lastly add the

filter cap.

> Take it one step a time.
> --
> Keith Bowers - Thomasville, NC

Most likely the inrush current is caused by the huge filter cap
trying to instantly charge to full transformer voltage. It looks like
an almost dead short to the AC side for a few cycles until the cap
starts to charge. With no load the transformer should draw a small
amount of magnetizing current and that's all. The inrush suppressor
will force the cap to charge through a series resistor that is
greater in value when it is cold. I have seen unrush currents in
large supplies what would actually cause the wiring to flex!