Where is the “smart” place to put an estop on a CNC mill? By smart place I mean in circuit. My switching power supply maintains energy for a good 5 seconds after unplugging the AC line. I also don’t want to “hurt” anything either.
Thanks!
Its a bit safer to estop by cutting off AC instead of the DC side of the power supply.
When cutting DC side power, the back emf voltage generated by a spinning stepper has no where to go thus can kill drivers. The power supply capacitors will usually absorb this energy and protect the stepper drivers.
Smaller nema17 motors don’t usually have this problem. A 3d printer nema17 motors spinning at 300rpm isn’t going to generate to much voltage. A larger nema23 spinning over 1000rpm can easily generate over 50volts.
Open the DC dc drive circuit to the spindle and it will stop pretty quick especially if it’s cutting.
I havent tried the same to steppers as I don’t consider them as dangerous.
Cutting DC power to the drivers is fine. It’s nothing like disconnecting or cutting the motor wires. The power and motor energy will dissipate in a fast, yet controlled manner.
a bit late, but:
I find that if my machine is moving, killing the ac side will drain the switching power supply basically instantly. If it’s idle it’ll take 5 or 10 seconds for all the lights to go out. Motors drain capacitors fast. Should be relatively easy to test, just have it start moving towards a dial indicator being recorded by a video camera, and hit the e-stop after the dial starts to move. Maybe I’ll do that tonight…
The bigger cnc machines often have an e-stop that’s interacting with software, so that it slams the brakes on before shutting things down, cutting the power just makes it coast for a while. Something else to consider.
@Chris_Chatelain ,I’d like to see that video. I haven’t done the work yet so I’m still contemplating where to put it. Let me know if you end up testing it.
@donkjr , I honestly don’t know what it is. It’s a 0-10vdc controlled motor controller. It outputs 0-100vdc to the motor from the 0-10vdc signal. I am however looking at this: 2.2KW Water Cooled Spindle Motor ER20 110V/AC Kit & 2.2kw 110V Inverter VFD 3HP & 80mm Clamp Mount & 75W Water Pump 110V with 6M Pipe & 14pcs / Set ER20 Collet for CNC Router Engraving Milling Machine https://www.amazon.com/dp/B0756WNP1J/ref=cm_sw_r_cp_apa_i_ijG.AbS7SZHY2
What’s your thoughts on It? I don’t want to spend good money after bad.
@Chuck_Comito the reason that I asked if you were running a vfd was because there are ways to brake the motor on those controllers but I have never done it.
I simply shut down my 24 & 48V with an Eswitch in series with the AC to them and it stops pretty quick. I havent tried it while cutting but I bet it is immediate.
I have looked at VFD multiple times but do not want to have to add coolant or put out another $400 and another controller. I decided to cross that bridge if I need more power which so far doesn’t seem to be the case. I also may consider using a dewalt router and manually speed control.
@Chuck_Comito one additional thing. If this is the one I am thinking of the 2.2KW is a beast (24lbs) and I am not sure my stepper can push it like I need.
Those are valid things to consider @donkjr … I really need to get a proper workshop so noise isn’t a factor. Otherwise I’d also be running a router. I’ll have to consider the weight ad well. I have a pretty beefy setup but an addition 24 lbs is a lot!