Based on a discussion I was having in another thread (but didn't want to hijack) my plan is to remove power directly from the drivers in the event of an e-stop via relays.
But as the steppers a likely to be moving then is this is problem for the drivers? I'm sending an e-stop to the BOB at the same time so the motors should be in the process of stopping.
Would it help if I added a capacitor across the relay coils to slightly delay driver shut down prior to the motors coming to rest - just a few milliseconds? Or am I worrying over nothing?
Does anyone else remove power to the drivers using relays in the event of an e-stop?
Edit: If you do want to go a little OTT then have e-stop turn off drive Enables so motors are still under torque and stop quick then remove power second or two later using a timer relay.!!
Last edited by JAZZCNC; 17-04-2015 at 09:24 AM.
In my layout (see post above) my relays are AFTER the PSU so there are no caps to drain and the drivers loose power immediately. So I either leave it, change to a relay BEFORE the PSU on the mains side which I think is what you are referring to, or add delay / capacitor across the existing driver relays on the DC side to hold them closed for a few milliseconds. Hope this distinction makes sense.
Well my way is to remove power by dropping out a contactor to transformer and send signal to control informing about e-stop so halting pulses.!
But in all honest your setup won't be a problem unless you intend traveling at high velocity and have a heavy gantry. So if you have it wired then wouldn't worry.!
Last edited by JAZZCNC; 17-04-2015 at 05:52 PM.
Ok, good to know thank you. Gantry is pretty light and feedrates aren't that high.
Capacitor mount brackets arrived today so roughly laid it out on the aluminium plate. Plate will be trimmed off just after caps, and before MCB.
I noticed that the toroid 2x24V AC cables are a much heavier gauge than the 240V AC cables so I'll match that heavy gauge with the DC cable out of the rectifier and over the caps.
It's a bit bigger than the blown SMPS it replaces but should still just about fit in the cabinet, top centre:
Joined the red and orange together and got 54V AC across the black and yellow, so that is the correct series connection.
I cut the red and orange cables back to leave about 60mm showing, stripped and tinned then ends then soldered together. Heatshrink over the join, then another long heat shrink over the top to finish the series connection.
Crimped terminal ends on the black and yellow cables for the rectifier. Had a look at the datasheet and the terminal rotated 90 degrees to the other 3 is the DC + output. Diagonally opposite this is the DC - output. The other 2 are AC inputs.
Marked out the holes for the cap brackets, rectifier, toroid and corner bolts and started drilling a few out. Went with M4 tapped on the capacitor bolts. Getting there slowly . . .
The MCB hasn't tripped out yet on the few times I've turned it on (6A type D) but since I haven't connected the capacitors yet that probably doesn't mean much.