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

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.

Jon