Last Updated on the 8th April 07


Stepper Drives, The Power Supply.
The first considerations were, how much power did I require and how did that break down into Amps and Volts. The LMD chips on the drivers are rated max, 55V, 3Amps. Thats 165 Watts for each driver. Mulitply that by 3 drives = ~500 Watts. I know that driving these chips near to the max voltage is likely to result in damage, so I'm going to back off from the max rating a fair bit, and shoot for around 36Volts.
36V * 3 drivers @ 3Amps = 324 Watts. My motors are rated at 1.3Amps each, so I won't need as much as this, but if I upgrade motors in the future, I'll want to be somewhere near that figure.
I found a transformer rated 300VA (2 * outputs, each at 25V, 6A) The outputs can be combined to give either (50V, 6A), or (25V, 12A). These ratings are all for AC current, we'll need to rectify the AC to DC and smooth it, this will alter the voltage by a factor of ~1.34.
So 25V * 1.34 = 33.5V. This was as close to my 36V as I could get without resorting to winding my own transformer. As it turned out, the transformer Actually output 28.33V. Once this was rectified and smoothed, it was 36.6V. Almost bang on target. I should easily be able to pull 10Amps through the transfromer. More than enough for my requirements.

The only part I purchased for building this power supply was the toroidal transformer, all the other parts were bits I had in my junk boxes. The other parts are:

  • Connectors
  • Bridge Rectifiers
  • Capacitors
  • A transfromer for the 5V logic supply
From left to right the parts are as follows: The Main toroidal transformer, a conneector for mains input (240V AC). Next is the bridge rectifier that converts the AC from the transformer into DC. The rectifier is sitting on a circular copper heatsink. A capacitor then smoothes out any ripples in the DC and feeds the power stage of the stepper driver. Then we have another transformer that supplies the 5Volt logic to the boards. Again this has it's own rectifier and smoothing capacitor. The copper block at the bottom is just for connecting all the earth points together.
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Warning. Fiddling with this equipment can kill you! Use this information at your own risk.