Re: [CAD_CAM_EDM_DRO] Router spindle electrical noise.

Eric,

Router motors are usually universal-type motors, which use brushes and
commutators. The electrical noise when the brushes move from one
commutator segment to the next is very high, and is caused by several
sources of inductance in motor wiring and the motor armature itself.

To suppress this noise, I added a small capacitor across the AC line,
inside the router itself, as close to the brush holders as possible. I
think I used a 0.01 uf (or mfd, depending on how old you are) 600V
cap. Higher voltage is better. Since the capacitor (I think) reduces
brush life, using as small a capacitor as you can is good. I started with
the 0.01 uf, it suppressed the noise well enough, and I haven't taken the
trouble to try a smaller value.

This cap must be right on the brush holders. Moving to back to the plug
will NOT suppress the noise. There is a LOT of RF radiated by the power
cord, and it gets into everything.

I've used a hairdryer (another universal motor) as a noise source for
informal noise immunity testing. Wrap the power cord around cables of
interest, turn on the motor, and see if the system continues to function.

Universal-motor RF generators would have been great spark-gap transmitters.

-- Carl

At 01:25 PM 10/19/2003 -0400, you wrote:

>Are you sure you are not experiencing "switch bounce"? Router motors can
>cause harmonic vibration that could cause a switch to start vibrating and
>trigger itself.
>
>----- Original Message -----
>From: "balsaman_cnc" <balsaman_cnc@...>
>To: <CAD_CAM_EDM_DRO@yahoogroups.com>
>Sent: Sunday, October 19, 2003 9:21 AM
>Subject: [CAD_CAM_EDM_DRO] Router spindle electrical noise.
>
>
> > The electrical noise generated by my Porter cable Router is
> > triggering my limit switch circuit. The limits are high and go low
> > if there is a problem. They are all in series (NC). If I set the
> > speed on my router down 20% or so the problem goes away. I slid one
> > of those ferrite donuts over the limit switch cable with no effect.
> > Is there something else I can try? I used shielded cable on all
> > cabling EXCEPT the limit switches...do I need to replace all that
> > cable? Are there other options?
> >
> > Thanks for any help you can provide.
> >
> > Eric
> >
> >
> >
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>OFF Topic POSTS: General Machining
>If you wish to post on unlimited OT subjects
>goto: aol://5863:126/rec.crafts.metalworking or go thru Google.com to
>reach it if you have trouble.
>http://www.metalworking.com/news_servers.html
>
>http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
>sister site to the CCED group, as many of the same members are there, for
>OT subjects, that are not allowed on the CCED list.
>
>NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING
>THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
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>List Mom
>List Owner
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Carl Mikkelsen
cmm@...
www.foxkid.net