re RF filters

Discussion in 'General Electronics Chat' started by woffler, Feb 27, 2010.

  1. woffler

    Thread Starter New Member

    Dec 24, 2008
    I need to reduce the noise on my cnc input power on my mill the power is 115 volts as i am getting to much noise to my control circuits . I need to reduce it as much as possible and i had read in a forum that guy's were installing rf filters on all a/c inputs on the same power source. I built the complete sys my self and used shielded cable on everything input signals and out put signals.But i am adding a new controller that is really fast and is highly sensitive to noise. Can someone please give me a littlre advise on this what to use and how to install the filters.

    Thank You Woffler:)
  2. russ_hensel

    Well-Known Member

    Jan 11, 2009
    There are pretty standard filters using a ferrite core and a couple of caps on the ac input to many power supplies. I have often salvaged them. I think google would find them for you. I also think that these may be available as pre built units. They both protect the circuit from noise input and if a switching supply stops the supply from putting noise out on the supply lines.
  3. Duane P Wetick

    Active Member

    Apr 23, 2009
    Recently, I worked on some flight simulator hardware that had extensive filtering and I can share some of that information with you. First of all a big nicely grounded LC can filter on the mains is necessary. On the inverter phase outputs, a 2-pass ferrite on each wire. Double shielded cable to the motor itself. And all enclosed in a mild steel Nema cabinet w/ silver impregnated gasketing. And its not over-kill either.

    Cheers, DPW [ Everything has limitations...and I hate limitations.]
    Last edited: Feb 27, 2010
  4. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    You can buy off-the-shelf filter units designed for use with inverter drives (motor speed controllers).

    One of those with an adequate rating for the machine could be a good starting point, it would get rid of a lot noise.

    The other thing you could add is a set of VDRs to clip any high-voltage spikes. You can get descrete parts or complete assemblies such as for lightning protection. One of those on the distribution board that feeds the machine will help if there is a problem with spikes.