LinuxCNC power failure protection

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25 Mar 2021 09:37 #203597 by deerefanatic
Hi all,

I am starting on a retrofit on my first CNC machine here shortly. I'm planning on using LinuxCNC for the machine. My location has 3 phase power from the power company, but I am literally the end of the line for the branch circuit that feeds me. I often have power disturbance issues where the power will flicker out for a second and then come back, sometimes just on 1 leg, other times all three. Yesterday it was bad enough that my manual lathe actually had the motor contactor drop out.

I had an idea to combat this somewhat for my CNC conversion.. Has anyone put a battery-backed power backup on their linuxCNC computer, then wired 3 relays to the incoming power legs, with their contacts in the E-Stop loop? My thought is that way, when the power flickers for a second, the control PC and mesa cards would stay powered on, and the machine would stop and stay stopped until manually restarted.

Thoughts?

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27 Mar 2021 01:44 #203765 by andypugh
I think that what you suggest should work. If you keep the encoders and LinuxCNC powered up then you won't lose position.

I imagine that at this point you would want to use "run from line" to continue the job. Apart from this being a bit flaky (you need to set up spindle speed, coolant, etc manually first) something you need to consider is keeping a record of how far through the program you were.

I think that a peak-hold on motion.program-line displayed in the GUI or Halmeter would be a help there.

A UPS that keeps 3-phase power live would be better. Most VFDs can run on DC input. As can most PCs and other switchmode power supplies. Maybe the answer is a mains-voltage battery bank.

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27 Mar 2021 12:44 #203802 by deerefanatic
I dont think a mains battery bank will work as this machine has a 60hp spindle and 6hp servo motors. ;) Its a CNC boring mill.

I believe I will investigate this more.

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27 Mar 2021 12:57 #203803 by andypugh

I dont think a mains battery bank will work as this machine has a 60hp spindle and 6hp servo motors. ;) Its a CNC boring mill.


It might work long enough.
A bank of 100Ah batteries would supply 100A for one hour. That sounds like plenty.
240V of 100Ah batteries would cost $2000 or so, though.

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28 Mar 2021 17:20 #203917 by deerefanatic
I'd probably be money ahead to just run the machine off of a propane genset. :)

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28 Mar 2021 19:59 #203935 by rodw

I'd probably be money ahead to just run the machine off of a propane genset. :)


A 24 volt DC 3 phase contactor with a UPS protecting the PC and the Mesa power should do exactly what you want. If the mains power trips, the contactor will need to be reset but the control side will remain powered up by the UPS for safety. This will mean when the power is restored, nothing will start automatically.

It might be better to use a safety relay in the mix as well.

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28 Mar 2021 20:23 #203939 by robertspark
I would suggest adding a means to monitor the voltage drop out, so that when the voltage drop occurs the current XYZABC etc axis positions and gcode line are recorded (saved to a file) so that the machine could be restarted from that position.

3D printers with Marlin firmware use / have that feature available.

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