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

-----Original Message-----
From: Jon Elson [mailto:elson@...]

>Roy J. Tellason wrote:
>>On Monday 22 March 2004 12:37 am, Jon Elson wrote:
>>>ibewgypsie wrote:
>>>>[Monster transformer causes excessive input surge and tends to fry

rectifiers]

>>>[use a series resistor on the secondary]
>>
>>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

If the resistor is N times larger, and the current is N times less, then
the power dissipated by the resistor will also be N times less.

Then again, if you actually want the same secondary current limiting
effect, the resistor must be N^2 times larger, not N times larger, in
which case the resistor will indeed have the same power dissipation.
-Kevin Martin