PSU question

[John S]

24 volts max and 5 to 6 amps

[Dwayne Dibbley]

24 volts max and 5 to 6 amps

Thanks John, is there a formula on how you reached that figure?

[JAZZCNC]

Think you'll find the formula is 20yrs experience and several dozen blown Allegro(A4988) chips.?

The Amp's is simple multiply the number of steppers Amp's plus a bit spare capacity.

The lower voltage is safety margin due to the allegro chip being notoriously bad at letting out the Magic smoke any higher. Coupled with the fact the next standard PSU will be 36V.

[Robin Hewitt]

There is a wonderful gizmo called the "crowbar circuit". You put a fat Diac across the PSU output and a zenner diode to trigger it should the volts rise above your max threshold.

When you trigger a Diac it stays triggered, hard on, until the Volts go away. A cheap Diac can handle lots of Amps.

In this case the Volts go away because the fuse blows. You then replace a 10p fuse rather than expensive hardware.
It's called a crowbar because the effect is like dropping a crowbar across the power input terminals

[Dwayne Dibbley]

The Amp's is simple multiply the number of steppers Amp's plus a bit spare capacity.

in that case as i have four steppers i should look for a 7-8A ( 1.7x4 + a bit ) ideally?

Thanks