# CNC AC Power Circuit Questions



## TomS (Feb 20, 2015)

I'm working on my CNC conversion and am at the point where I can wire the AC power circuit.  I don't have much electrical smarts so I've done quite a bit of web surfing and reading the posts on this forum to learn as much as I can.  I'm still trying to figure out some of the details.  

I've drawn a circuit diagram (below) to help me explain what I've got in mind for the specific reason of getting feedback from the experts on this site.  Comments and criticism are welcome.  For clarification the AC input will be switched.  Didn't show the switch and a few other details to keep the drawing simple such as a fuse block. Didn't shw the fuse block because I'm not sure where it should go.  I'm thinking it should be wired in the line side of the circuit between the relay and power supply.  And speaking of fuses what fuse rating should I use?  Two of the power supplies are rated at 6A and one is rated at 7A.

Thanks for your help.

Tom S


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## DMS (Feb 20, 2015)

Few questions and comments

1) When you say 6A and 7A, is that on the AC input side? If that is on the AC side, you will be pretty close the max capacity of a 120V circuit (25A typical)
2) What is the reason for 3 separate relays? 
3) I don't understand the reason for the DC PS feeding into the relays for the X/Y axis power supply. If I understand the arrangement, as soon as the AC power is switched on, the DC supply will come on, actuate the relays, and then the other power supplies. The only advantage I could see to this is to stagger the startup, but the power supplies should not pull much current without a load connected.

I would consider changing the arrangement as follows

1) replace the 3 relays with a single relay, feeding all 3 axis supplies.
2) Have the DC PS connected directly to turn on the fans.
3) Connect the relay input to your CNC controller through a physical EStop button like this one

http://www.automation4less.com/store/proddetail.asp?prod=2ALMPP4LB-024

So that you can cut power to the machine axes if things go pear shaped.

As for the fuse, I would put it between the AC input and everything else. Add it on the line side (hot). Make sure you have a nice solid ground coming in, and if the enclosure you are using is metal, make sure you secure that ground solidly to the enclosure at a clean metal surface (scrape off some paint if you need to).


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## TomS (Feb 20, 2015)

DMS said:


> Few questions and comments
> 
> 1) When you say 6A and 7A, is that on the AC input side? Yes. If that is on the AC side, you will be pretty close the max capacity of a 120V circuit (25A typical) I agree.  Do I need to have more than one 120V circuit feeding this equipment?
> 2) What is the reason for 3 separate relays? I was following jumps4 CNC build.  I'm probably wrong but my understanding of his build was that's what he did.
> ...



Here's a picture of my control panel.  I've stripped out the KM2 and KM3 contactors and their associated wiring and switches.  My plan is to feed the AC circuit in my AC circuit drawing above by tapping into a 120V lead off of KM1.  All other circuitry will remain such as power on/off, spindle on/off and forward/reverse, and emergency stop.  What do you think of this?  

Thanks for your questions and input.  I don't have any electrical experience and need all the help I can get.

Tom S.


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## jumps4 (Feb 20, 2015)

Just a note I found out by accident
the e-stop turning off the ac to the power supplies may not stop machine motion instantly.
 dc power supplies have capacitors in them that take some time to discharge and motion can continue for what seems a long time when things are going very wrong. The e-stop that i found that works the fastest is to an input pin to the pc. It stops sending pulse and motion commands so all motion stops.
I don't know what controller software you are going to use, but stopping the program stops the machine the fastest.
I entered a bad line of code when I first built my machine and hit the ac power switch on my controller to stop it, to my amazement the machine just kept moving until the power was depleted.
Steve


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## DMS (Feb 20, 2015)

I'm guessing the box you show is part of the existing mill? Steve's comment about not stopping when AC is cut is a good one. 

I guess whether the motors are on at full torque on startup depends on the type of motor, and the type of driver. With my motors and drivers, they are dissabled until I enable them, so startup current is nearly 0.

I might also suggest that if you have not selected your axis power supplies, then finding some 220v input supplies would reduce the amount of current you need. 

Overall, I think you are on the right track. Keep us posted.


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## TomS (Feb 21, 2015)

jumps4 said:


> Just a note I found out by accident
> the e-stop turning off the ac to the power supplies may not stop machine motion instantly.
> dc power supplies have capacitors in them that take some time to discharge and motion can continue for what seems a long time when things are going very wrong. The e-stop that i found that works the fastest is to an input pin to the pc. It stops sending pulse and motion commands so all motion stops.
> I don't know what controller software you are going to use, but stopping the program stops the machine the fastest.
> ...



Thanks Steve.  This is the type of information that comes from experience, which I don't have.

Tom S


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## TomS (Feb 21, 2015)

DMS said:


> I'm guessing the box you show is part of the existing mill? Steve's comment about not stopping when AC is cut is a good one.
> 
> I guess whether the motors are on at full torque on startup depends on the type of motor, and the type of driver. With my motors and drivers, they are dissabled until I enable them, so startup current is nearly 0.
> 
> ...



Yes, the box shown is the existing control box.  

FWIW my stepper motors and drivers are the same as what Steve used in his mill conversion.  Maybe he can clarify if the motors are enabled at startup as I wouldn't now how to determine that.  

I did some searching and found that my power supplies are 110V/220V capable.  I had assumed they were 110V only.  

I have another thread going on the Precision Mathews forum showing my CNC conversion.  Here's the link. http://www.hobby-machinist.com/threads/taking-the-cnc-plunge.24858/

Thanks again for responding.  

Tom S


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## TomS (Feb 28, 2015)

Bear with me as I know just enough about electricity to get myself in trouble, and I did.  I started on the wiring and thought I had it figured out until I powered up the 220V circuit.  Pushed the Power On button and nothing happened.  Checked the E-Stop to make sure it was in the run position, which it was.  Pushed the button on the contactor and the spindle started.  The spindle starting and probing with my multimeter confirmed the contactor had 220V feeding into it.  Then checked the 24V transformer and nothing.  Looked over the wiring and determined that the transformer originally was fed 220V from KM2 and the 24V feed into KM1 was also fed from KM2.  When I stripped out KM2 and KM3 contactors and associated wiring the end reult was that I had also eliminated the transformer circuit.  Doh!! 

Now this is where I can use your help.  I have to figure out a new circuit to feed the transformer and then get 24V to the contactor.  I don't think the feed circuit is too difficult as the transformer data plate sort of explains what needs to be done.  The plate is hard to read in this picture but I did confirm what I'm writing is what's on the plate.  In the manual (attached) the picture on page 25 below the plate shows that on the input side 110V is connected to terminals 20 and 21 orange block on top of the transformer).  For 220V you connect to terminals 20 and 22.  I'm going with 220V (as original) but does it make any difference which terminals I connect the line and neutral to?

Terminals 30 and 31 are the 24V out feed (orange block on the bottom of the transformer).  I searched the net and can't find any wiring instructions on the contactor.  I'm at a loss here.  What terminals do I connect the 24V feed wires to?  Again is polarity an issue?

Besides the picture of the control box (before KM1 and KM2 removal) on pages 26 and 27 there is a wiring schematic and a description of how the circuits were originally designed .  

Thanks for your help.

Tom S


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## JimDawson (Feb 28, 2015)

The coil terminals on the contactors should be labeled A1 and A2.  It is common practice to connect the 24V common (0 volt, blue wire in this case) to A2.  In an AC circuit, the polarity doesn't matter.  If it were a DC circuit the A1 would normally be marked +, and A2 would be marked -, these marking may be on the contactors  even though they have AC coils.

I'm not exactly sure if I answered your question, but it's late.  
.
.


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## TomS (Feb 28, 2015)

JimDawson said:


> The coil terminals on the contactors should be labeled A1 and A2.  It is common practice to connect the 24V common (0 volt, blue wire in this case) to A2.  In an AC circuit, the polarity doesn't matter.  If it were a DC circuit the A1 would normally be marked +, and A2 would be marked -, these marking may be on the contactors  even though they have AC coils.
> 
> I'm not exactly sure if I answered your question, but it's late.
> .
> .


Thanks Jim.  I'll take a look at the contactor in the morning.

Tom S


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## jumps4 (Feb 28, 2015)

TomS said:


> FWIW my stepper motors and drivers are the same as what Steve used in his mill conversion. Maybe he can clarify if the motors are enabled at startup as I wouldn't now how to determine that.



On my mill I did use the enable circuit, so if mach3 is running and not in e-stop the motors are braking. If mach3 is not running and the controller power is on the motors are not braking. My controllers have a half power at idle setting, if I remember correctly, so they wont heat up at idle.
Steve


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## TomS (Feb 28, 2015)

jumps4 said:


> On my mill I did use the enable circuit, so if mach3 is running and not in e-stop the motors are braking. If mach3 is not running and the controller power is on the motors are not braking. My controllers have a half power at idle setting, if I remember correctly, so they wont heat up at idle.
> Steve



Steve,

Thanks for the clarification.  I'm slowly working my way through wiring this thing up.  Hasn't been as hard as I thought but still have a few hurdles to get over.

Tom S


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## TomS (Feb 28, 2015)

jumps4 said:


> On my mill I did use the enable circuit, so if mach3 is running and not in e-stop the motors are braking. If mach3 is not running and the controller power is on the motors are not braking. My controllers have a half power at idle setting, if I remember correctly, so they wont heat up at idle.
> Steve



Steve,

Thanks for the clarification.  I'm slowly working my way through wiring this thing up.  Hasn't been as hard as I thought but still have a few hurdles to get over.

Tom S


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## TomS (Feb 28, 2015)

TomS said:


> Steve,
> 
> Thanks for the clarification.  I'm slowly working my way through wiring this thing up.  Hasn't been as hard as I thought but still have a few hurdles to get over.
> 
> Tom S





JimDawson said:


> The coil terminals on the contactors should be labeled A1 and A2.  It is common practice to connect the 24V common (0 volt, blue wire in this case) to A2.  In an AC circuit, the polarity doesn't matter.  If it were a DC circuit the A1 would normally be marked +, and A2 would be marked -, these marking may be on the contactors  even though they have AC coils.
> 
> I'm not exactly sure if I answered your question, but it's late.
> .
> .



It worked!!!  Thank you Jim.  Connected the input power to the transformer and ran a wire from the 24V common to A2.  Another hurdle down.  A1 was already wired through the power switch and E-stop.  The spindle runs in reverse.  Unrelated to the transformer/contactor issue but I'll tackle that later.

Started wiring the relay and power supply circuit and the fans.  After that it's the control wiring.

Tom S


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## stupoty (Mar 1, 2015)

The fuse should be located imediatly after the mains input connector, if its hard wired to a distribution panel and the cable size is the same as the cable feading it you don't need a fuse, the cable probably gets smaller from the contactors, so as their is a cable size change to a smaller size that would want to be fused. E.g. Big cable comes in covered by big fuse, splits into multiple smaller feeds to psu's each psu feed gets a fuse.

What do the contactors do ? In the drawing it looks like you have no way to turn them off?  (Sorry if thats a silly question).  Ow i think I just saw the season for the contactors in a reply, I would personaly go with a big switch unless you wish to be able to power it up and down from software.  

Stuart


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## TomS (Mar 1, 2015)

stupoty said:


> The fuse should be located imediatly after the mains input connector, if its hard wired to a distribution panel and the cable size is the same as the cable feading it you don't need a fuse, the cable probably gets smaller from the contactors, so as their is a cable size change to a smaller size that would want to be fused. E.g. Big cable comes in covered by big fuse, splits into multiple smaller feeds to psu's each psu feed gets a fuse.
> 
> What do the contactors do ? In the drawing it looks like you have no way to turn them off?  (Sorry if thats a silly question).  Ow i think I just saw the season for the contactors in a reply, I would personaly go with a big switch unless you wish to be able to power it up and down from software.
> 
> Stuart



I have two 15A breakers that I plan to wire between the main power input and the terminal block feeding the power supplies and fans (one 220v 30A circuit in then split into 2 15A feeder circuits).  The power supplies are 110/220 volt capable.  I'll have to run a 110V circuit for the fans.  Fuses will be in between the terminal block and the individual devices.  Does this make sense? 

I'd like to power everything with 110v but the one circuit I have available is nearly maxed out with the equipment I have now.  Eventually I plan to add a 4th axis power supply and a coolant pump and who knows what else.   My options are to run another 110v circuit or use the 220 I have available at the mill.  I'm open to suggestions from the more experienced electrical people on this site.

The original spindle contactor power on switch, power off switch and e-stop wiring is still in place.  This circuit works as it came from the factory.  I'll post some pictures of the AC wiring layout later today so you can see what I've done.

The power supplies are 110/220 capable.  The X and Y axis supplies have a 110/220 selector switch.  The Z axis has a DQ2722M power supply/driver but no input voltage selector switch.  My question is: how do you adjust for 110v vs. 220v input voltage?  Does it adjust automatically?  Is it a dip switch setting?  I searched on-line but couldn't find an answer.

Thanks,


Tom S


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## JimDawson (Mar 1, 2015)

TomS said:


> The X and Y axis supplies have a 110/220 selector switch. The Z axis has a DQ2722M power supply/driver but no input voltage selector switch.



That power supply automatically senses the voltage.  Just like most modern computer power supplies.  I am using the same drive on my press project.


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## TomS (Mar 1, 2015)

JimDawson said:


> That power supply automatically senses the voltage.  Just like most modern computer power supplies.  I am using the same drive on my press project.



Thanks


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## TomS (Mar 2, 2015)

Here are a few pictures of what I've done so far on the wiring.

The first picture shows the X and Y axis power supplies and drivers and the Z axis power supply/driver combo unit.  I've roughed in the AC power to the power supplies and DC transformer.  The open space in the upper left hand corner is where the breakout board will go.  Also left room for an A axis PS and driver.  



This picture is of the rear panel showing the layout of the two 15A breakers, 110V receptacle, the fans and the X, Y and Z motor plugs and wiring.  The three open holes are for the limit switch aviation plugs.



I relocated the power panel from the mill head to my rollaway that has the electrical and electronics in the bottom drawer.  I'm going to put a monitor and laptop on top.  I've got excess flexible conduit so I can move the rollaway about 7 or 8 feet away from the mill so I don't have to worry about chips and coolant fouling the computer. 



Still have quite a lot to do bit I am making progress.

Thanks for looking.

Tom S


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