[jamezwarner]

Hi there,

I'm trying to chase some sporadic USB faults with my smoothstepper driver on a large rack&pinion DIY gantry router table. VFD+ 2.2kw spindle

The problem seems to come from a new airblast system I've built using a fridge compressor, plastic airline and a welding nozzle...

The issue seems to get worse over several hours of use, at which point the USB driver will error within 5mins of a cut. The issue seems to go away when the air system is off..

It's electrically isolated from the rest of the system, sharing a ground at the compressor end, and the compressor runs continously. I will try a ferrite ring on the compressor power cable, but I'm wondering given the way it gets worse as time goes on, if it's static buildup at the nozzle? Would grounding the tip dissipate this do you think? I'm not sure if it's building up on the hose itself (which runs down the cable tracks with all the other sensor cables)
Many Thanks,
James

[Al_The_Man]

What do you mean by its 'isolated from the rest of the system'?
Your P.P. and USB port is at the same reference or common to one side of your AC to the compressor and any other AC motor or device.
This is due to the P.C. P.S. being at Earth ground as well as any AC device due to the neutral at Earth Ground also.
You need to bond or equi-potential bond all metal work on the machine to a central point, together with the service ground conductor.
Al.

[jamezwarner]

By isolated, I mean the airline is all plastic, the only connection between the systems is the mains ground.

Would it be worth regrounding all parts to a single point ground? (even if otherwise grounded) Things like my breakout board/ smoothstepper are grounded to the metal cabinet, which in turn is grounded via the PSU... What about things like proximity sensors?

James

[Al_The_Man]

That is the general recommended method.
http://www.automation.siemens.com/do.../emv_r.pdf?p=1
Al.

[John Bennett]

You might be just building up a static charge with the air friction against the plastic pipe (also a problem with central vacuums and dust collection systems) Normally you run a bare stranded copper wire along the side of the piping, starting at the nozzle and going back to a grounding rod or pipe. This wire should be held tight to the piping at intervals to absorb the static charge.

[RomanLini]

I agree with John Bennett it sound slike static buildup in the plastic pipe.

I think the wire would need to be inside the pipe where the air is moving.

On my air setup I saw some static issues when first using it, but then put a 7 foot length of 1/2" copper plumbing pipe in the middle length of the plastic line, to cool the air and after that saw no more static issues. My plastic line is some garden hosepipe and some polypipe, and the copper tube.

Also changing the type of pipe may help, some plastics are bad for static and others not so much.