I built my PS by purchasing a Toroidal transformer and rectifier module from Antek Inc. For a 30V x 20A power supply, you would need a 20-22volt transformer outputting 600 Watts. This type of transformer is designed to handle overload conditions typically 2x the rated output, and can output 20% higher rated power when run on 60hz instead of the rated 50hz, so a 600 watt transformer when run on 60hz (US) is actually a 720 watt transformer and can handle overloads of 1200 watts (50 hz) or 1440 watts (60 hz). When building a power supply like this, the AC RMS voltage when used with a bridge rectifier and smoothing capacitors will have a DC output voltage about 1.41 times higher than the AC output by the transformer.
I would recommend the following items ...
Antek DC80 - 80vdc 35A bridge rectifier module $25.00
and your choice of the following transformers
Antek 5220 - 500 watt (50 hz) 600 watt (60 hz) 20vac output (~28.2 vdc output) $55.00
Antek 5222 - 22vac output (~31.02 vdc output) $55.00
Antek 8420 - 800 watt (50 hz) 960 watt (60 hz) 20vac outpup (~28.2 vdc output) $84.00
Note: their 600 watt transformers are either 18v or 24v ac output putting you a bit too high or low if you are targeting about 30vdc output.
One possible option is to use these transformers with multiple rectifier modules to create multiple lower wattage outputs. For example, the 800 watt power supply has four AC outputs. You could use these to create four 200 watt power supplies, two 400 watt power supplies, one 600 watt plus one 200 watt power supply etc. What I mean by this is that you could create an output for each servo driver so each driver is on its own rectifier module (and set of capacitors) minimizing the effect of power draw from one motor to the next ... to a point that is anyway.
Putting together one of these is extremely simple. You hook up line voltage to the input wires on the transformer, connect the output from the transformer to the input terminals on the rectifier module, then connect wires from the output terminals on the rectifier module to your servo controllers, and to be on the safe side, connect a wire from the negative output of the rectifier module to ground to eliminate the ground path from going through your servo controllers, and to make everything more stable.
The advantage of this type of power supply vs a switching power supply is that it will not shut down on overload. I had a problem with a switching power supply a while back that I traced down to auxiliary capacitors. Sometimes the switching power supply would shut down a few seconds after startup. It was the charging current going into the capacitors triggering the overload circuit in the power supply. I had to remove input power to the power supply to reset it, but had no guarantee that it would power up again. I replaced this setup with the one described above and couldn't be happier. In my case, I built a 720 watt power supply with both 40v and 80v outputs for a total of $110 including shipping that can handle a 1440 watt overload for 60 seconds.
Take a look at their site. I have no affiliation with them, I am just a happy customer.
Thanks - John Z  |