How much more auxiliary power can I add?

Hey everyone,

I’m trying to keep this question as simple and straight forward as I can. Hopefully I’ll be posting more about this in the future.

The plan is to do some upgrades/projects on the PCNC440, mainly right now some interior lighting and I have an idea to add additonal door alarm sensors on the side doors (since the machine is being used in academia and may have students using it). I have some options in components so everything will be low power. One of my goals with this is that I’d like the parts to look like it came from the factory.

I’ll likely be adding either a 12VDC/5A or 24VDC/2A; 60W power supply for the LED lighting. I’d like this to possibly turn on with the Disconnect Switch. Similarly, either with a second power supply or dual output, a 3VDC or 5VDC for a microcontroller to monitor the door alarms. It also appears the door alarm might operate on a 12VDC (but if anyone has more info on this I’d appreciate it) switch so I’ll be using a relay. I’ll also likely expand the DIN channels to a few more for these.

I also know there is a 24VDC Power Supply already installed on the unit, but I do not believe it will provide enough power. Likewise, I know there is the 48VDC Power Supply (and what its max is) but I do not know how much of this power is being used. For this reason I haven’t considered using this as my “starting” power and stepping it down to my required voltages.

I am reviewing the available documents and components but I also want to ask others about this.

My “concern” lies with the OEM equipment and whether it is rated for adding an additional two power supplies essentially. If there is enough “headspace” as it were. I believe the only OEM components I’d be running through in this fashion are the AC Power Cord and the Disconnect Switch. As mentioned, I’ll be adding one or two more channels tied into the 120VAC channels, so I do not see this as being a possible limitation.

I hope that was clear and I appreciate any help and thoughts on the matter.

Anything that needs 5v can be run on usb ports. Led lights, micro controllers and such.

Be careful running on USB power. Any computer has a certain available power on the USB bus. Once you go over that then the USB power will fail

@Joe I would just caution you that electrical modification can void a warranty. If you are going to continue down this path, I would caution against tapping into any supply. Assume that there is no headspace, would be the general rule. Perhaps look into adding a supply. There may be some members of the community that have added a supply to their machine, that could assist on this one.

I appreciate the responses.

I know some things can run off of USB power but I’d like to keep the power within the electrical cabinet. Plus there are varying needs here. I know I can just buy a LED light strip kit, with it’s own power supply and all, off of Amazon but simply I don’t want another “On/Off” switch to think about. Part of the goal of this project (with the LED lights) is to be able to turn the machine on and immediately have lighting inside the cabinet. I know I’ve seen John Saunders at Saunders Machine Works/NYC CNC and others who have done similar, but I was looking to do something a bit different than what I’ve seen so far.

@SamBollen Thank you for the heads up since that is another concern I have. We do have the machine under warranty and plan on continuing that for as long as we can. If I can ask for some clarification on what you consider “supply”? My mindset is to have a different power supply for these things, especially since that 24VDC Power Supply would provide no where near enough power to handle a LED light strip. Hypothetical, if I were to add a 12VDC External DIN Power Supply to the electrical cabinet to power an LED light strip and microcontroller, and I get my power from the #100 (110VAC) DIN Channels (to power the 12VDC Power Supply), is this still considered tapping off a power supply then? To me the power supplies would only be one of the existing ones such as the 24VDC or 48VDC Power Supplies.

Basically, I would be adding a power supply in the electrical cabinet. The only components I’d otherwise worry about here is the Voltage/Amperage/Power Ratings of the AC Power Cord, Disconnect Switch, additional DIN Channel. That is, the “headroom” isn’t so much on one of the existing power supplies, but the power rating of some of the components.


Unfortunately, this is a completely unsupported endeavor. Hopefully someone in our community here will be able to chime in.

The PCNC440 has provisions for the 110V bus to run a 110V coolant pump through a relay that sources from the same power bus you are wanting to tap. Do you have a coolant pump/system? Is your 110V to 12VDC 5A power supply going to draw as much power as one (unlikely)?

Alternately, you could put the lighting on a separate 110V power source which is powered by a relay or contactor that turns on when it sees voltage flow to the main power bus from the main disconnect.

@SamBollen I completely understand. I still appreciated your input.

@Ashraf_Farrag Thank you for your comment but we do already have the coolant pump (and ATC) set up (the 4th Axis is also wired up but that hasn’t been tested or used yet). As for how much power the 12VDC Power Supply will use, well that’s up the LED lighting (predominantly; as I don’t expect the microcontroller and its components to be drawing much). I’m basing my power consumption of the LED lights from the manufacturers.

Putting the lighting on a separate bus from the main disconnect is what I’m going for. I don’t work with DIN systems all that much so I apologize if I’m using the incorrect terminology. I’m just not looking to daisy chain between too many components or draw too much power on a component I’m overlooking.

You could use a wireless dust collector trigger in order to avoid any additions to the DIN rails. Power comes on, it detects it and triggers the remote module to turn on lights. About $150 or so.

You are plugged into a 15A 120V socket in the US, so one would expect there to be no greater than that in overall current draw. The wire size of the plug into the machine and through the disconnect should be rated for standard 15A and I would imagine the DC is rated to 15A. The question is how much load is the other stuff at peak and can the DIN bus cope with another 2A at 120V.

The spindle is roughly 5A, so you have 10A left for the power supplies while they are operating. The ATC doesn’t operate while the spindle does. Throw a kill-a-watt on the machine while running and see what you need to run compared to 15A plus some safety margin.

Yes, we’re using 120V 15A here, so it shouldn’t be drawing more than 15A. From what I can tell most of the components are rated for higher than this. I’m a bit more familiar with DC circuits so I don’t know how much of these electronics are “cumulative” in power. I’m also assuming that I can ignore the DC Out Power since this should be part of the AC Power In(?). Sorry, this is a combination of me getting side tracked and thinking out loud.

Looking at the components it looks like the VFD is rated for 6A Input (I don’t know if Tormach will like me listing parts and their ratings).

I did a bit of testing today and I was thinking about trying the Kill-A-Watt. I wrote a little program that moved X, Y and Z with the Spindle at 10,000 RPM and Feedrate of 135 in/min. I also ran the Coolant Pump. The only other thing I could think of which I didn’t have connected, was the 4th Axis. Essentially trying to run the machine at its maximum, although without any material to mill so the machine didn’t have a “load” in that sense.

I was reading about 6A to 6.5A from this.

I’m still looking at options, but it appears I’m only at about half the current draw. Regardless, I want to keep any additional current draw on this to a minimum.

Although if it does appear that I’m adding too much current on this I may go with what you suggested before and use a relay but with a second external power power supply.

Here is my simple attempt at the program that moves the spindle around (also attached). (502 Bytes)

O00001 Repeat[5] (Machine Maximum Power Test for PCNC440)
(T31  D=0.125 CR=0. - ZMIN=-0.0394 - flat end mill)
G90 G54 G64 G50 G17 G40 G80 G94 G91.1 G49
G20 (Inch)

(G54 is Machine's Absolute Zero Coordinates, Top Left Corner)

N10 (XY Perimeter)
N11 T31 G43 H31 M6
N12 S10000 M3 M8
N13 G54
N14 G0 X0 Y0 Z0
N15 G0 X0.25 Y-0.25 Z 0.25 F135
N16 G0 x9.75 Y-5.75 Z-3
N17 G0 x9.75 Y-0.25 Z0.25
N18 G0 X0.25 Y-5.75 Z-3
N19 G0 X0.25 Y-0.2 Z0.25

O00001 Endrepeat

M9 M5

My background is aftermarket automotive electronics (among other things) which is almost exclusively 12V. I would think that you are good to go.

My lights are on the power strip that the computer is on for my 440. That’s an even simpler solution.