Re: [CAD_CAM_EDM_DRO] Re: welding machine as a power supply

On Monday 22 March 2004 01:14 pm, Jon Elson wrote:

> Roy J. Tellason wrote:
> >On Monday 22 March 2004 12:37 am, Jon Elson wrote:
> >>ibewgypsie wrote:
> >>>Probably, the best thing would be 3 smaller individual transformers. I
> >>>got one large 2kva 220/24+24=48(dual tap) transformer and it weighs
> >>>about 50 pounds. It cost about $200 Local. Problems with one large
> >>>transformer is the bridge, you want to use a 35amp 600 volt cube for
> >>>simplicity. I have lost 3 of them in a year. When the capacitors are
> >>>discharged and you hit the go relay and throws power to the drives,
> >>>charges the capcitors (looks like a short for a second) it fries the
> >>>cube one time outa a hundred. I tried dual switches that would charge
> >>>the capacitor bank half wave but quickly tired of it.
> >>
> >>You can connect a couple Ohm resistor between the bridge and the
> >>capacitors. Have a time-delay relay short the resistor after one second.
> >>This will reduce the power-on surge by a factor of 100 or so.
> >
> >Yeah, but since power dissipation in the resistor is current-squared
> > times the resistance, putting it on the primary side is probably a
> > *much* better idea...
>
> Nope. You get no benefit that way, as then you need a resistor that is
> N times larger, where N is the winding ratio of the transformer. The
> dissipation will be identical on either side of the transformer. That's one
> of the corollaries of using a transformer.

Huh? I don't see how you figure that...

This doesn't make any sense to me.