Confirming PSU spec for steppers.

[irving2008]

For safety reasons don't use a toggle switch for the 'start' switch on the 24v supply to relay 1. It must be a momentary push to make to enable both relays and use a contact on relay 2 to lock it in, as I drew it.

Why? your machine hits a limit switch, triggering estop (or you hit estop). everything turns off. You turn off the power at the main isolator but in your desire to see what happened you forget to turn off the 'start' switch. You reset the estop, or move the machine off the limit switch and turn on the main isolator... but the start switch is still closed so the 70v rail comes up and the machine starts moving again because you forgot to stop the PC...

Its a safety interlock, it mustn't remain in an ON position. Also you don't need both contact on Relay 2 to drive Relay 1, only one side of the coil needs to be switched.

[Rogue]

For safety reasons don't use a toggle switch for the 'start' switch on the 24v supply to relay 1. It must be a momentary push to make to enable both relays and use a contact on relay 2 to lock it in, as I drew it.

Ahhh. The reason why I basically re-drew your drawing was to get my head around what was happening. Now you put it like that I can see what is happening there. I guess I should have asked. It's not like it's the first daft question I've had :)

Also you don't need both contact on Relay 2 to drive Relay 1, only one side of the coil needs to be switched.

I know, but I wasn't using those poles for anything else at the time and it looked untidy. I was envisaging the second poles driving a relay that disconnects the bleed resistor when the system is running.

Using my imagination I've imagined some of that same 24v running thru E-stop going thru limit switch's as well and the RL2 relay having another contact for the 5v signal from BOB.!!

Running the limit switches off the E-stop wire sounds like a good idea - they are effectively doing the same thing as an E-stop, after all. However, I've come across a few discussions about the BoB, with several people saying that it would be better not to cut power to it.

Edit: Oh and you'll need an limit override momentry button in there as well to allow reversing off the switch's.

I guess that might help...