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K40 groundloops issue that causes usb comms issues

Just for those with comms issues, here is a post of a common issue within some k40s.

Missing Ground story #2: Several of the popular K-40 laser cutters that’s I’ve seen employed a questionable ground strategy. The incoming AC receptacle has a ground wire, but instead of going directly to the metal chassis, it goes to a binding post; and INSULATED binding post. If the chassis is grounded, at all, it’s via an internal connections in the power supply module or perhaps thru the interface board. Consequently lot’s of communications problems as the chassis is essentially being ground thru the USB cable.

See https://hackaday.com/2017/03/09/wtf-are-ground-loops/

Cheers, Paul awesome.tech

Just spoken with Cohesion3D and they have encountered the same issue with ground loops. Basically the K40 machines with broken grounds, introduce a current through the negative/gnd of the usb cable and the laptop or PC. That introduces electrical noise which limits or distorts the communication.

Ray suggested :

" use a separate 24V/4 Amp power supply and remove the 24v from the K40 power supply and keep the common gnd to allow the laser to fire.

  1. Do the same issues still exist?

  2. Does it depend on whether the second psu is grounded?"

I still see a common problem here where current flows from k40 earth to external earth and introducing noise (laser power supply and via the usb cable to laptop/PC).

So grounding the k40 chassis to remove the earth currents is still the best solution. Next to this I would suggest to rewiring the k40 motors/power/limit switches with shielded cables.

Unfortunately a cheap price for the k40 also includes quality issues and no support from the sellers. For us it's difficult to assess since we cannot physically inspect the machine. So I will keep expanding the troubleshooting cart. Wonder where to post it since a lot of content get lost in the threads. Maybe a new blog post? Let me know what you think, Paul

Cheers, Paul awesome.tech

Do you think a direct ground from the controller to the case would help with this as well?

Hi Gregg,

The ground (min circuit) on the Gerbil is connected to the min circuit on the laser PSU.  I don't think the min circuit on the PSU equals the ground circuit of the K40. You can use a multimeter in Ohm setting to check this (with K40 turned off of course).

Cheers, Paul awesome.tech

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