Re: [CAD_CAM_EDM_DRO] backward transformer

On Wed, 16 Jun 2004 12:09:04 -1000, you wrote:

>I have a large transformer that came out of a 48 volt power supply. It
>has three output leads, the two center taps are hooked together, the
>voltage reads 37.5 from center to either side and 72 end to end. however
>when I hook up a 25 amp 250 volt bridge rectifier it reads 33.5 volts
>center to end and 67.5 volts end to end. I thought the rectifier would
>increase the voltage by 1.44. why is it going backwards?

You need the capacitor to charge to peak voltage, otherwise, you get
whatever your DC meter can read of a pulsating unipolar sine wave.

This is based on vpeak of a sinewave is 1.414 * vrms. A lightly
loaded supply (or no load) allows the capacitor to charge to peak
voltage. A more heavily loaded supply will deliver less voltage.

The typical meter will not read peak, but somewhere around an average
dc value, less than that peak value. The capacitor makes all the
difference, the meter will read what it will....

Harvey

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