Compressor tripping control board


I’ve been using my Shapeoko for around a year now without having any issues at all, but i’ve recently been doing some processes where i have a need to blow air as i’m cutting.
Unfortunately when my compressor starts up, it sometimes trips the control board, causing the machine to stop instantly, and require a reset.

I was just wondering if anyone could suggest an easy fix for this. I’m in a location where i don’t really have the option of utilising separate mains circuits - so i was hoping that there may be some kind of device i could plug in between the compressor and mains to mitigate spikes and surges, or alternatively, whether i should consider upgrading the psu to the Shapeoko to increase resilience.

As i said, i’ve never had any real problems with the machine before, so i don’t think this is related to interference, missed steps, or anything technical. The machine just stops dead, and vanishes from the control software without any messages, so i think it is just a power disruption.
I’m in the UK so i’m using 230v 60hz AC.

Any suggestions would be appreciated…


A low capacity UPS (uninterruptible power supply) would protect from short term mains dips (brown outs), actual trips (black outs) and also give protection from spikes and noise on the mains supply. Guess at budgeting $200+ for something that will keep your spindle/shapeOKO/laptop running for the seconds or maybe minute(s) that your trips cause


Hi Andy,
This is a great (and actually rather obvious in retrospect :face_with_raised_eyebrow:) suggestion.
Thanks a lot.

Depending on the compressor size and HP is it possible to move it to another circuit. If it is a very large compressor the voltage drop might be unavoidable but if it is just a small pancake oil less type why is it dropping voltage enough to cause your controller to go off line. Is it possible that you are getting static from the moving air and it is EMI causing a USB disconnection. If that is the reason you can get a usb isolator. You could also ground your router body and dust collection.

Reading between the lines;

If your mains circuit is marginal, then switch-on and switch-off surges are going to be a fact of life for you. If you go the UPS route, the VA capability is going to depend on whether you want to power the spindle through it or not - the typical Makita/DeWalt is about 1KVA and the ShapeOKO and PC likely about 200 maybe 300 VA. The ‘switched in’ types are likely to be cheaper than the ‘permanently online’ types. Work backwards from either your $ budget or your KVA budget, with that choice made look at how long you want power to last for. I don’t know if there is a special/uprated mains wall socket required, some places in the world require it.

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A possible option to reduce the load might be to use a battery operated trim router — folks have used these successfully (and it’s neat to be brushless), though usually w/ a wired in power supply — really wish that the wire in power supplies were more accessible/affordable.

Thanks for the follow ups - but i’m certain that this isn’t a capacity issue. Although i only have one circuit - it’s good for at least 16a.

I normally run a 1.5kw spindle and a vacuum without issue.
On this occasion i was only running a diode laser and no vacuum.

Unfortunately it seems like the abrupt start up of the (small) compressor is putting some kind of momentary spike through the mains power which is disrupting things - it can’t be too severe though as it only affects the CNC in like 1 out of every 5 switch-ons.
I’m feeling confident that a small capacity UPS should smooth things out enough to solve this issue.

I’m not sure what i’ll do if it doesn’t though - I’ll update this thread either way…

I missed this response.

Hmm, it is just a small compressor, and as i said above, unlikley to be a capacity issue - so this does seem likely. The spindle is grounded, but a ‘usb disconnection’ sounds like the best description of what is happening.
I’m not really familiar with USB isolators. I see some being sold on Amazon as a hifi / audiophile accessories. Should i just buy one of these? Or is there a particular sort that i should be looking for?


I would suggest that the compressor is not doing a very good job of snubbing the big spike of electrical noise it generates whenever the motor is turned on or off, that’s then travelling back through the wiring and being broadcast as electrical noise using the wiring as an antenna.

I’d start off by putting a noise filter onto the compressor’s input power as electrical noise is generally best managed at source.

I’d use something like this

There are versions already housed in extension cords, they tend to be Belkin / APC level of overpriced though.

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A cordless compressor is also an option if considering a cordless router. I’ve been using my 18v Ridgid brushless compressor (not continuously running).

This is very likely, because the cut-out does always coincide with the turn on of the motor.
Thanks for the suggestion. I’ll give it a try.

The usb isolator can keep usb disconnects from happening. If you live in a cold climate with low humidity you tend to get more. It is like walking across the carpet and the door knob shocks you. If you dont think it is the usb then dont buy but they isolate your usb and if the cause is static and/or in the future it is a cheap alternative to losing your connection.

I once lived in a 1920 house that was remodeled in the 70s. When the air conditioning kicked on my 35 inch tube tv would shrink from the voltage drop. There was no ground just a two wire system. The original knob and tube wiring was in the attic. I think the house had only 5 circuits total. Maybe one outlet per room and half the house on one circuit. Modern houses have 5 outlets in one room and 20-40 individual circuits. Motors take a lot of current to get going causing your voltage drop. Once the motor gets up to speed the current is 1/3 of the start up current required. The bigger the motor the bigger the current pull. A compressor could be on a compression stroke when you power it on and that takes maximum current to start compared to the piston going back down to draw more air in.

The power supply for the Shapeoko uses a range of voltage to work. The AC is converted to DC power and the regulators keep the DC voltage constant. However if the voltage drops low enough the power supply shuts down the DC voltages. As some suggested a cheap UPS could keep you out of trouble and on the rare occasion the power goes off your project is not ruined. With the UPS you can pause and write down the line number and depending on your UPS rating keep running and/or shut down and save your place and edit the gcode to start at a good restart point.

Thanks for your answers one and all.

Although i didn’t run the machine extensively this weekend. I did run my laser for a while under the exact same conditions, and the EMI filter as suggested by @LiamN seems to have done the trick - since i didn’t experience any disconnects even with the compressor cutting in and out quite regularly.

Hopefully that will be the end of this thread, but i did get a low capacity UPS as well, which will remain on standby as the next thing to try if this problem comes up again…