Re: [CAD_CAM_EDM_DRO] Re: More on Re: Insulating D-shell from chassis?

Is the spindle motor a universal, brush-type motor? If so, then your
spindle is one of the best, broad band, high energy transmission devices
and noise generators known to man.

I tried line filters at the plug end of the power cord, but they did
nothing. There was too much energy radiated from the power cord, which
coupled into everything.

To suppress this noise, I attached a small capacitor (say, somewhere on the
order of 1 to 10 nanofarads, I forget the actual value) directly across the
brushes inside the motor housing. Nothing I did outside the motor housing
could reduce the radiation. Start on the small side, and see how well the
noise is suppressed. I had a scope, so I could observe the noise on (all)
logic lines.

I don't think this is a ground-loop kind of problem. This is much higher
frequency, and probably comes from radiated RF. Suppressing the RF at the
source is the best way to reduce the problem.

The cap might lower brush life, but I haven't seen signs of it yet on a PC
laminate-trimmer type of tool. There could be a better filter designed,
taking into account a better model of the motor impedance, but I didn't
bother. The smallish cap completely squelched the noise.

-- Carl


At 08:04 AM 11/19/2003 -0800, you wrote:

>At 12:27 AM 11/19/03 -0600, Jon wrote:
>
> >I would make a first guess that the spindle drive is conducting EMI onto
>the
> >power line. If you can come up with an interference isolator (often used
>as
> >part of a power input module on high-end computer and instrument gear)
> >and put it in the line to the spindle drive, i bet it will clean up the
> >problem.
>
>Yes, I have a number of inlet filters and tried them on the spindle, driver
>box and PC singly and in combinations, and that did nothing to improve the
>problem.
>
>Best regards,
>
>Randy
>
>Randy Gordon-Gilmore ,----.___________ ______________ _________________
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