Re: [CAD_CAM_EDM_DRO] EMI Rehab (Caps over brushes?)

Abby Katt wrote:

>
> Thanks Tom!
>
> I'm still wondering what to do about placing caps over the sherline's DC
> spindle-motor brushes.
> Do I just wire a cap over the two power wires, or connect caps to the
> brushes themselves?
>
> Thanks!
> Abby

*********************

Hello Abby,

I don't know about the capacitors.

I put a toroid on my Sherline 5410 CNC mill spindle power cord to reduce
sensitivity to transients. The best kind is like a short tube and you
thread your power cord through it. But that only works if one end of the
cord is unwired. You will see these on many computer video cables as
part of the cable. I think you can even remove and recycle the toroid
from a video cable.

The type I used opens and closes so that you can clamp it around an
existing power cord. That is not as effective has the type that cannot
be opened. But, it was easy to install. Cost was maybe $5 at a local
surplus electronics store.

I don't know if that toroid helped but it was cheap and does no harm. I
think that my system got better when I replaced the printer cable with
one that was shorter, had every pin wired, and was shielded.

I also routed the spindle power cord away from the parallel port cable.
The electrical noise from the spindle motor radiates out of the spindle
and the power cord which acts like a transmitting antenna. Those
transients are picked up on the parallel port cable which acts like a
receiving antenna. if the spindle power cord and the parallel port cable
must be close to each other then avoid running them close and parallel
to each other. Routing them perpendicular to each other will minimize
signal coupling between them.

You can aggravate the noise by laying the spindle power cord close to
and/or parallel to the parallel port cable then running the spindle at
max RPM. When I ran the spindle at 2400 RPM instead of the max of 2800
RPM my noise problems went away. That was helpfull while I figured out
how to make the system more noise immune.

Tom Hubin
thubin@...