Re: Power supply softstarts

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Graham Stabler" <eexgs@n...>
wrote:

>
>
> I am building a 6 axis system with linear servo motors and have
> bought a pair of 500VA transformers which should provide 50v and
> sufficient amps for peak acceleration. I have also got a 100,000uF
> capacitor for smoothing although I may increase this.
>
> On my previous homebrew power supply I added a softstart that
> charged the output capacitors via a resister until they were up to
> voltage. The prevents a nasty thud on turning on the supply.
> However I have a feeling that with the two transformers in this
> supply in parallel I may have more of a problem with the

transformer

> inrush current which does more than make a thud!
>
> What is the "best" way to produce a soft start on the primary of my
> powersupply. Should I just use a contactor, timer and power
> resister to provide a current limited supply to the transformer on
> power up?
>
> Thanks in advance for any help
>
> Graham

One of the biggest problems is toroidal transformers. Due to the fact
that they maintain the polarity at the point when they were switched
off there is chance of a big inrush current depending on where you
are in the cycle at switch on. A basic soft start could be created
using a zero-crossing switch. I would also put a small resistor in
series with each of the primaries to take the surge.

Regards

David Goadby