What's in your control box

[mikes]

Newbei here again, so thanks for listening...

I am starting the design of my control box, and after looking at some posts by others, I wanted to get some ideas on best practice for the design. This is for a CNC router with VFD powered spindle motor working off single phase:

• I have been planning on keeping the VFD outside the control box as I thought the EMI/RFI it generates would be an issue for other electronics. However, I see others are using a contactor to control power to the VFD and both are in the control box. Thoughts?

• Thus far, I was not planning on using a contactor to disconnect power to the VFD, partly to KISS, but also I am not sure if the e-stop should physically cut power to the VFD or instead use the VFD braking in an e-stop situation. What is best practice?

• What about manual tool changes and disconnecting power to the VFD? Is that where a contactor should be leveraged.

• I have been thinking of using a separate 120VAC power cord for the control box (controller and stepper controllers), and a different 240VAC circuit for the VFD. Is it more common to use one leg of the 240VAC to get 120VAC and just have one power cord to the machine? In that case, is it usually brought into the control box and distributed as needed? I suppose most PSUs can also work off 240VAC.

• I fear I may have already made a newbie mistake in selecting a switching PSU for powering my stepper controllers. However, the steppers are 4 amps x 3, and it is a 17 amp supply, so I hope it will suffice. It's a Meanwell, so not total junk. I realize it's not about supplying enough current, but dealing with the motor induced currents. Thoughts?

• Should I use individual fuses for each stepper controller?

• E-stop - I am still a bit confused as to how best to leverage the Acorn provided e-stop functionality. Is this not software controlled? I thought an e-stop should always be independent of the controller as a firmware error could inhibit the e-stop functionality. That is not to say that the controller shouldn't be an input to the e-stop circuit. What is best practice here?

What other considerations come to mind when designing a CNC router control box?

[martyscncgarage]

Let me see if this works, my personal comments below your points:

Newbei here again, so thanks for listening...

I am starting the design of my control box, and after looking at some posts by others, I wanted to get some ideas on best practice for the design. This is for a CNC router with VFD powered spindle motor working off single phase:

• I have been planning on keeping the VFD outside the control box as I thought the EMI/RFI it generates would be an issue for other electronics. However, I see others are using a contactor to control power to the VFD and both are in the control box. Thoughts?

Suggest you follow the schematics that Centoid provides. It is pretty common to put the VFD in the control cabinet. Use shielded control wire and at the control end solder a green wire to the shield's drain wire and take all those to ONE common point.

• Thus far, I was not planning on using a contactor to disconnect power to the VFD, partly to KISS, but also I am not sure if the e-stop should physically cut power to the VFD or instead use the VFD braking in an e-stop situation. What is best practice?

See above...

• What about manual tool changes and disconnecting power to the VFD? Is that where a contactor should be leveraged.

You can hit estop if you want during a tool change....

• I have been thinking of using a separate 120VAC power cord for the control box (controller and stepper controllers), and a different 240VAC circuit for the VFD. Is it more common to use one leg of the 240VAC to get 120VAC and just have one power cord to the machine? In that case, is it usually brought into the control box and distributed as needed? I suppose most PSUs can also work of 240VAC.

I have done this but if you use a logic power supply that accepts 240VAC no need to suggest you fuse it.

• I fear I may have already made a newbie mistake in selecting a switching PSU for powering my stepper controllers. However, the steppers are 4 amps x 3, and it is a 17 amp supply, so I hope it will suffice. It's a Meanwell, so not total junk. I realize it's not about supplying enough current, but dealing with the motor induced currents. Thoughts?

You should be ok, but there is some worry about back EMF, I will let the router guys chime in on this one.

• Should I use individual fuses for each stepper controller?

You could ahead of the drive itself. You would need to calculate the fuse size based on the load.

• E-stop - I am still a bit confused as to how best to leverage the Acorn provided e-stop functionality. Is this not software controlled? I thought an e-stop should always be independent of the controller as a firmware error could inhibit the e-stop functionality. That is not to say that the
  controller shouldn't be an input to the e-stop circuit. What is best practice here?

In the commercial controls Estop can do several things. 1) send a signal to the motion controller about the E-stop input, the control will respond accordingly. 2) Drop power to the motor drives 3) shut down coolant pumps, 4) Can shut down spindle motor especially when not VFD contolled (contactors)

What other considerations come to mind when designing a CNC router control box?

There are many different ways, start with the Acorn schematics for your drives and go from there. Everyone will have a different idea and may provide more ideas. These are mine in brief for what their are worth. Don't take them as gospel....

Bottom line, use good judgement and common sense, especially when working around your machine.
Marty

[footpetaljones]

With a line filter and shielded cables, you shouldn't have much problems with EMI.

You should be good on the amperage. Most recommendations I've seen are the sum of your motor amperages *.6.

Fuses/circuit breakers are very much open to being placed however you want. If you are trying to squeak every bit of power out of the motors you can get, definitely run individual fuses/CB's. If you're going to take it easy, you should be OK with one on the PSU. Protecting each driver separately is a bit safer in my opinion. If you have one 12 amp fuse on the PSU there's nothing stopping one driver from trying to pass 8 amps for whatever reason.

You can run an Estop button that has 2 NC contacts. One going to Acorn and one killing a contactor that power for the drives and VFD runs through.

If you haven't seen it already, I'd recommend you watch Sam's playlist of him wiring his PM727 here:https://www.youtube.com/playlist?list=P ... 24P3itDdS6

[mikes]

If you haven't seen it already, I'd recommend you watch Sam's playlist of him wiring his PM727 here:https://www.youtube.com/playlist?list=P ... 24P3itDdS6

Thanks!

[jazzcnc]

Here's my way of doing it.

E-stop should kill or shut down anything that can hurt you. This should be Hardware controlled not software driven. It should also then inform the controller that E-stop condition occurred which then shuts off its Outputs and stops code running etc. It should not Kill power to the controller.

In case of VFD, it's not good to Kill power. So the E-stop should inform the VFD to Stop in a controlled manner.
Also because of the way VFD's work shutting the power off won't work because the capacitors inside will still power it for few more seconds until drained. So informing it an E-stop occurred and also to apply braking if need be is fastest and best option for stopping spindle quickly.
You could if wanted put this on timed Relay which then shuts off power after safely/quickly brought to stand still but IME it's not required.

The E-stop System, along with limits, guards etc should be part of Latched Reset circuit which won't allow Reset unless all are clear and safe.
Here's where my thinking may be subjective.? My thinking is that Limit triggers are not E-stop conditions but more positional errors by often by programming or jogging errors. So shouldn't be part of the E-stop system and left to the controller to deal with rather than killing power.
However, not everyone thinks the same so you choose which suits you best. But let me tell you if new to cnc then Jogging into limits when learning is very easy to do, esp on a smaller machine, and killing power soon gets boring.

Contactors should be used for high current devices like drive PSU and VFD. Depending on the drives/motors you might want to Kill Power or just disable the Drives using Enable feature. This will depend on machine really. For instance, you may want the motors to still Hold torque so axis doesn't drop but still disable any Inputs which allow it to move.
With Stepper based system on a router, I would personally Kill power to the drives.

Fuses on the drives are a safer option, using too many fuses won't hurt anything, not fusing can be expensive.!!

Regards VFD in case etc then this comes down more to good practice. If you use Filters, shielded cable and good grounding/cable practice ie: Star grounding and cable management then you won't have any issues.

Hope this helps

[mikes]

Here's where my thinking may be subjective.? My thinking is that Limit triggers are not E-stop conditions but more positional errors by often by programming or jogging errors. So shouldn't be part of the E-stop system and left to the controller to deal with rather than killing power.
However, not everyone thinks the same so you choose which suits you best. But let me tell you if new to cnc then Jogging into limits when learning is very easy to do, esp on a smaller machine, and killing power soon gets boring.

I think I am in agreement with you regarding the limit switches not being part of the e-stop system.

I like your idea about a delay on the VFD contactor, but that does mean you are totally relying on the VFD to do the right thing (not fail in some negative way during an e-stop). I guess if the VFD did fail, it would not be actively braking or driving, so maybe this the best solution.

I will say, I am a bit surprised at all the variations. I would have thought there was basically one right way to wire an E-stop.

[martyscncgarage]

Here's where my thinking may be subjective.? My thinking is that Limit triggers are not E-stop conditions but more positional errors by often by programming or jogging errors. So shouldn't be part of the E-stop system and left to the controller to deal with rather than killing power.
However, not everyone thinks the same so you choose which suits you best. But let me tell you if new to cnc then Jogging into limits when learning is very easy to do, esp on a smaller machine, and killing power soon gets boring.

I think I am in agreement with you regarding the limit switches not being part of the e-stop system.

I like your idea about a delay on the VFD contactor, but that does mean you are totally relying on the VFD to do the right thing (not fail in some negative way during an e-stop). I guess if the VFD did fail, it would not be actively braking or driving, so maybe this the best solution.

I will say, I am a bit surprised at all the variations. I would have thought there was basically one right way to do wire an E-stop.

Take the time to go look at the All in One DC schematics. You'll see how they control everything. They are far more detailed than Acorn. Take some time to follow things. Look at the CNT1 relay, basically an Estop relay, you can see what goes through it. Esentially Servo motor power, the common for the VFD and any ancillary things you might want to shut down. Estop button has two contacts. One direct input to AIO DC and one that controls this relay. Gives you some good ideas. You could roll with the 220/110 VFD schematic and put Acorn in the place of ALL IN ONE DC

http://www.centroidcnc.com/centroid_diy ... oller.html

Marty

[mikes]

Take the time to go look at the All in One DC schematics. You'll see how they control everything. They are far more detailed than Acorn. Take some time to follow things. Look at the CNT1 relay, basically an Estop relay, you can see what goes through it. Esentially Servo motor power, the common for the VFD and any ancillary things you might want to shut down. Estop button has two contacts. One direct input to AIO DC and one that controls this relay. Gives you some good ideas. You could roll with the 220/110 VFD schematic and put Acorn in the place of ALL IN ONE DC

Marty, thanks for the recommendation. I will give them a close look.

[DICKEYBIRD]

I will say, I am a bit surprised at all the variations. I would have thought there was basically one right way to wire an E-stop.

Spoken like a true politician. "Hi, I'm Mike & I'm with the government; I'm here to help."

Definitely something that needs fixin' by the gub'mint with new rools & reguhlashuns.