Quote Originally Posted by jcb121 View Post
So the steppers run at 50v and 4.2A. so i will need something that can output 50v at 12.6 Amps. Multiply those to together, so I need over 630 watts/VA?
The steppers run on 50V, but a transformer rated for 50V is 50V rms and you're rectifying the output and storing in a capacitor so the output voltage is actually close to the peak voltage, i.e. 50*2^0.5=70.7V. In reality you get a bit less than that due to the forward voltage of the diodes and numerous other factors. This means you can actually use no greater than 50/2^0.5=35.4V. A 36V (or one with two 18V secondariness placed in series) might be fine, but really it's too close to the limit so from Rapid the nearest is 30V, 88-3838. 32V (or 16+16) would be good too.

Next consideration is the current. For 3 motor a 500VA (or greater) transformer will be fine as it's actually a lot less current than you'd intitially expect. I recently tested with the same motor on 48V and the maximum continuous current (with the motor at full power) was just over 1 amp. You need more than that in reality for the peaks, hence 500VA is fine.

Quote Originally Posted by jcb121 View Post
A lot of the transformers I've seen run off 230v instead of 240v,
Don't worry about the difference between 230v and 240v - it's insignificant as the 10% tolerance on the UK mains voltage encompasses that range. Often the transformers have two primary windings so you can put them in series to get 230V or in parallel for operation from 115V.

The circuit is widely available. Just the transformer, a bridge rectifier and electrolytic capacitor. For example:

http://www.cnccookbook.com/img/Lathe...ySchematic.jpg