I've got two PSUs on my system. Both are grounded to a stud on the metal chassis which also has the mains earth. It would be easier if I could ground the shielding for cables at the motor end as I am also grounding the steppers. Will this cause problems or make no difference? I'd normally thought grounding at the controller end would be best.
bearer last edited by
Shouldn't make a electrical difference as long as there is a low impedance path from the motor end and back to the same stud you have mains earth on.
The benefit of a true star topology is easier troubleshooting as you can pick and choose what to ground from one spot, and its also a single point of failure which in this instance is a good thing, if there is a problem, you know exactly where it is.
Thanks. That's fair enough. To ground the shield you can use the bare drain wire can't you?
The machine is low impedance. Zinc electroplated mild steel. My meter (basic fluke) is a bit crap at that low level of resistance but all points on the machine read 0.3ohms or less and shorting the leads reads 0.1 ohms.
For future machines with multiple PSUs I will need to add a terminal block to distribute the power better. This one is reasonably simple as I realised the arduino relay boards are rated high enough DC current to allow me to cut (relays opening while 'hot' on fault or e-stop only) on the DC side.
bearer last edited by bearer
To ground the shield you can use the bare drain wire can't you?
You can, and if you have foil shield then thats the best option. If you have braided shield I normally put a sleeve on the braided shield, crimp a lug on the end and screw it to my chassis or terminal strip. Its just more sturdy than just the drain wire.
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I realised the arduino relay boards are rated high enough DC current to allow me to cut (relays opening while 'hot' on fault or e-stop only) on the DC side.
Might be overkill, but for saftey functions you may want to consider adding a "crowbar" to short out the supply, this is to ensure a zero voltage potential if the relay is welded or somehow other short circuits provide alternative supply paths. Or at least beware that asking a high power DC relay to break a circuit for safety isn't a 100% sure thing.
I appreciate that contacts can weld, and to mitigate that a little I will fuse before the contacts. Part of the reason of doing this on the DC side is to remove the need for a second (/3rd, v0.6 have nosiey 5VDC regs) power supply and not loose the fans on fault trip.
On my static machines I will have a dedicated power supply, will switch on the AC side, and will consider a crowbar on them. Thanks.