Confirming PSU spec for steppers.

[Rogue]

Smoothing Capacitors:

You need C = 0.1 * A/V for a 5% ripple = 0.1 * 12/70 = .017F = 17,000uF with a voltage rating of at least 100V and a ripple rating of 12A. (for derivation see here)

Doing this in one capacitor is expensive (18000uF, 400v, 12A ripple = £271!!!) So usually you make it up with a bank of capacitors in parallel. The exact value is not critical so 3 x 5000uF @ 100v/4A would do, or whatever you can get cheap on eBay :)

For example, 3 of these: Buy Aluminium Capacitors GP Al electrolytic capacitor,4700uF 100V Epcos B41456B9478M online from RS for next day delivery. would be £33, with the matching mounting clips @£1.70 for a pack of 5. hese have screw terminals so you'll need the appropriate solder ring tags.

Thank you, that's very, very useful. I was looking at caps that cost about £3 each though, is there an important part of the spec that I didn't take into account?