Re: [CAD_CAM_EDM_DRO] Transformer Soft Start

Hate to disagree with both of you but...I saw exactly this problem on a PSU
that I built a couple of years back - there was absolutely nothing wrong
with the way it was wired up (single primary, and you have to try pretty
hard to mis-wire a bridge rectifier & a capacitor), but I had to use a much
larger mains fuse than I had expected in order to deal with the inrush
problem. At the time, this was a simpler solution than using an inrush
limiter (I didn't have one to hand, but I did have a bigger fuse) but I
will fit one when I can remember to add one to my next components order &
will then replace the fuse with one of the correct rating.

Regards,
Tony

At 12:03 03/07/2003 -0400, you wrote:

>Jon,
>
>I agree.with you. Likely problems I'd be concerned about:
>
>1) Transformer is actually shorted
>2) Split 230/115 primary is wired with one of the primary coils reversed
>
>If the transformer is shorted, you probably can't tell with an
>ohmmeter. Even a single loop that is shorted will cause the current to be
>too high. In effect, a single shorted loop looks from the primary AC side
>as if the primary is shorted. There could be several ways to test for this
>with an ohmmeter. One might be to connect a 9V battery to one coil, and
>watch in the dark for a spark as the battery is removed. A shorted
>transformer won't make a spark, but a working one MIGHT. A good, healthy
>spark would be a good indication that the transformer itself is OK.
>
>I like your idea of a 220V bulb, and would use that to test the primary
>phasing. I'd disconnect the secondary winding completely, and leave it
>open. I'd connect the primaries in series, and also in series with the
>bulb. If the light is lighting (after a few seconds) after applying AC
>through the bulb, I'd reverse one of the primary coils and try again. If
>the light goes out, the transformer is not shorted, and the primaries are
>phased correctly. If the light stays on both ways, then the transformer is
>bad.
>
>-- Carl
>
>At 10:42 AM 7/3/2003 -0500, you wrote:
>
>
> >tiffyted wrote:
> >
> > >Can anyone in this group advise me on a suitable circuit for soft
> > >starting a 230v primary, 40v secondary 1000VA toriordal transformer.
> > >
> > >I have one I want to use with my Gecko 201's, but it keeps blowing
> > >the mains fuze on power up.
> > >
> > >
> > >
> >I think you have something serious wrong, here. I don't think soft start
> >will help you. it is possible the transformer is defective. Are you sure
> >it has a 230 V primary? Is it a split primary, 2 coils that can be
> >wired for either 115 or 230 V? If so, an incorrect connection in either
> >setting will blow fuses. The phase of the two windings must be correct
> >for it to work.
> >
> >First, I'd disconnect the secondary wires and see if the problem still
> >ocurrs. If not, then most likely the rectifier is bad or wired wrong.
> >If it still blows, you need to check the primary wiring with the
> >manufacturer,
> >or with someone who has successfully used the same transformer on 230 V.
> >
> >If you can't get any help on this, wire a 230 V light bulb in series with
> >the transformer primary. If the bulb glows at full brightness, the
> >transformer
> >must be appearing as a short. With the recifier/capacitor connected, it
> >should glow brightly for a few seconds, and then begin dimming as the
> >capacitor slowly charges.
> >
> >Jon
> >
> >
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>http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
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>OT subjects, that are not allowed on the CCED list.
>
>NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING
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Regards,
Tony