Confirming PSU spec for steppers.

[Rogue]

Just out of interest, if you wanted to get 5V out of that system as well, would you run a 7805 off the +24v circuit, or should that circuit be kept purely for the relays/e-stop?

[irving2008]

Just out of interest, if you wanted to get 5V out of that system as well, would you run a 7805 off the +24v circuit, or should that circuit be kept purely for the relays/e-stop?

Depends. The 24v is present as soon as the primary switch is turned on. If its OK for the 5v to be present too, and the current drawn is small, say < 0.1A, then yes. Otherwise I'd run a small 5v supply off the aux AC.

Incidentally +24 is nominal. A 15v transformer would give 21v, an 18v transformer would give 25v. A 3VA transformer is more than enough (200mA output). The smoothing capacitor need only be 470uF @ 40v rating and needs no bleed resistor. The relays are 24v, 600ohm coil, needing 40mA each, with 7A 4PDT contacts.

[Rogue]

Intriguing, and hopefully stripboard friendly! I think I will start here before attacking the bigger stuff.

Here we are talking about mA: would the same 35A bridge resistor still work? Or would it be too "robust" (for lack of knowing what the appropriate term may be) in this situation? Does there come a stage when the safety margin becomes so excessive that it degrades performance at the lower end of the operating range?

[irving2008]

Intriguing, and hopefully stripboard friendly! I think I will start here before attacking the bigger stuff.

Here we are talking about mA: would the same 35A bridge resistor still work? Or would it be too "robust" (for lack of knowing what the appropriate term may be) in this situation? Does there come a stage when the safety margin becomes so excessive that it degrades performance at the lower end of the operating range?

You mean 35A bridge rectifier. It would but one that size is needless. This one is more than sufficient and cheaper.