Re: [CAD_CAM_EDM_DRO] Power Supply Guidance Needed

On Monday 13 March 2006 02:44 am, Larry Olson wrote:

> Ron,
> Thanks for the input. I have e-mailed the good people over at
> Acme to get the white papers on the transformers I have. I should know
> more tomorrow. If they put out 70V and are rated for 120V input than I
> am in business. I understand you can parallel the output from 2 of the
> same transformers if the impedance is within a few percent of each
> other. Do you have any idea how to measure it? I was thinking of
> paralleling 2 of the 3 transformers that I have because I think they are
> around 1000VA or so.

If the transformers in question are not identical, then the one with the
higher voltage output will fight with the other one, not a good situation...

> I have 6 5400uF capacitors on hand that are larger than a soda
> can that I would like to use. I figure about 4 of them if I'm thinking
> correctly. Also there was a 50W 750ohm bleed resistor across each set of
> caps (3 sets of 2ea.). Do you think one will be enough or should I put 2
> in series to handle the extra current?

Putting resistors in series will make them have less current, not more. If
you put them in parallel, then they'll handle more current. Figuring out
what you need here is simply a matter of using Ohm's law -- take the maximum
voltage that you expect to see and divide it by the resistance and that'll
give you the current flow. Volts times amps will give you the power
dissipated by the resistor. Putting two of them in parallel will draw twice
the current.

> One more question. If I have a 2500KVA transformer (or 2 smaller
> ones) what kind of amp draw will it have on 120V?

Take the transformer's secondary voltage and figure out the ratio to the
primary side -- the current draw on the primary side is the same ratio, only
the other way around. For example (picking easy numbers out of the air) if I
had a 12V transformer with 10A output then on the 120V side it'd have only 1A
of draw (plus transformer losses, but I'm ignoring those for the moment).

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