USB Serial Disconnects and Humidity (A Easy Fix)

I use to get USB Disconnects a lot (Fall of 2015), and Carbide3D sent me a new GRBL board (2.4) and that solved 99.9% of my problems. I NEVER get a disconnect cutting metal, but I wood (pun) get them once in a while when I cut wood, but I was never able to pinpoint the exact cause…until yesterday. The humidity in my shop was 12% and I went from almost never getting a disconnect to getting one almost every few SECONDS.

I raised the humidity to 50% and then ran 500,000 lines of code without a single disconnect.

I then took a spray bottle and lightly sprayed the inside on my enclosure to increase the humidity locally (inside the enclosure) and this also worked as well (as increasing the humidity in my workshop)

So, in short, the next time you are plagued with USB disconnects, the fix might be as simple as a few sprays of water. (or adding a humidifier to your shop)

Hope this helps!

PS I have sent this information to @Jorge so that a fix can be found

PS2 I had several additional ground straps but since the wood (Black Walnut) was also very dry, the ground straps were useless. Perhaps the static was being generated between the 1.0 face mill and the router…like a Van de Graaff generator…


Really interesting, I have a similar issue - the last few months I have been getting disconnects - since the drop in temp for winter (give or take). I have sent a replacement board this week - I’m now wondering if my garage is too dry, or too humid… I had been keeping a large silicone bead bag in the enclosure when not in use…

Yeah, we’ve noted the increase in disconnects w/ the change in the season, and have been noting it as a potential culprit — guess I’m lucky to have mine in a basement where I struggle to keep the humidity to 45%, or outside.

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I forgot to add that you can even spray a little water onto the wood stock and that also helps a lot, and it doesn’t change the overall humidity level of the wood that much.

Interesting point on humidity. Now that I think about it I may have experienced this in the past.
I was also sent a new board, a year or so ago. Disconnects never completely stopped but the frequency dropped considerably. Then I attached a 25’ vacuum hose, disconnects became more frequent. Searched the forums, ran a ground wire thru the vacuum hose, disconnects dropped back to an acceptable level. Then, almost two months ago now, I attached a ground wire to the case of the DW611, haven’t had a single disconnect since.
Ran a 2.5 hour job yesterday, white oak, humidity at 7-9%, no disconnects. It will be interesting to see if this continues (no disconnects) for the next week or so since it is expected to continue to be quite dry here in So Cal.


I attached my ground wires to just about every place inside my exclosure…except the router, and now that I think about it, it IS a 2-wire plug, so a ground wire could help. Thanks!


Super dry air here in Colorado Springs, CO. I don’t get disconnects, but…on my list to buy now is anti static hoses for my dust boot and shop vac. I’ve found that if I use my vac while cutting, the static generated will absolutely cause a disconnect. I also cannot touch any part of the machine while running with my bare hands, or the static discharge will cause a disconnect.

I too, probably need to take a look at grounding wires and straps.


I replaced my router cord with a 3 wire, and added a a ground to the router metal body. I don’t know if it helped anything, but I haven’t had any problems (Minnesota)


Prior to my crash - I checked my levels, humidity is not close to 10% more like 45. I did a quick spray before changing my board but still get the issues. New board in and it was fine till I killed it…

Static discharge increases as humidity decreases. You need to provide a safe path for such a discharge. Se my post Random Controller Disconnects


I installed ferrite cores over any cable and ran tinned 1/4” bonding braid from my router mount to Z axis, Then tagged all axis’ rails back to the original power supply. I purchased a refurbished desktop to control the machine. With early version boards this helped minimize the disconnects to an “acceptable “ level.

Since upgrading to the v2.3 and 2.4 boards, I have rarely experienced a disconnect. I think I’ve had 3 or 4 in the past year when the humidity drops, mostly when doing tool changes, fortunately none while running a job. We use our machine over 60 hours a month and had to buy another to help keep up with product demand.