voltage change factor

[dummer]

I need to build a power supply for a CNC machine. I've been told that the resultant DC voltage will be slightly higher than the non-rectified AC. Can someone tell me the precise factor used to compute the new voltage?

[Staigen]

Hi dummer, velcome to the forum, nice to have you here ;D

The DC voltage is roughly the square root of 2 times higher, minus the
voltage drop across the rectifier diodes, when properly smoothed, and
without a load.

//Staigen

[dummer]

The DC voltage is roughly the square root of 2 times higher, minus the
voltage drop across the rectifier diodes, when properly smoothed, and
without a load.

Could you show the math? Let's say the AC voltage came out of a transformer at 40VAC.

[Staigen]

Hi

Oops, that was a BIG question, there are written a whole book about it, but i will
try to show you. first we have to talk a little about the transformer, it have 40 V
out only at its rated current, at low or none current output it have larger output
voltage, that you have to measure. But lets say that you have a ideal transformer
that have 40V output at all its current output up to its rated load, then the
rectified and smothed output DC voltage is 40 times 1.41 = 56.4 minus the drop
over the rectifier diodes, about 1.2 V = 55.2 Volts at zero current. But, due to the
transformer is rising its output at low or zero output the voltage is going to be higher.
Hope this solve some of your questions.

//Staigen