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Mini-lathe causes exteme electrical interference!

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  • Mini-lathe causes exteme electrical interference!

    My Homier 7x12 lathe causes exteme interference on all radios in the house and in the shop. It even affects portable radios running on batteries!! I just started using it but the noise it creates on a radio is extremely annoying. I figure that it must be possible to remove this noise by some type of filtering. Has any one experienced this problem? Any suggestions? Thanks!!!!!

  • #2
    Yup. Classic RFI. First check with other Homeir owners to see if your problein is typical. If not, complain to the manufacturer and obtain what remedy you can.

    If the you get no satisfaction and you wish to keep the machine you need to enclose all non-metallic electrical parts in metal shileding and install RFI filters where the line enters the enclosure. It's a lot of work to do the job well and neatly but it will solve the problem.

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    • #3
      Get a power bar that advertises that it has noise filtering and run the machine from that. A good deal of the RFI is transmitted via the house wiring which acts as an antenna. Wrap as much of the the power cord as you can tightly around a steel bar or better yet a piece of iron. Tape it in place.
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      • #4
        That machine has an internal speed control, some form of SCR or PWM setup. The RFI/EMI may or may not be coming out on teh power cord. Very likely it is, possibly there are other leakage points. Power cord is usual, since the wavelength is so long for AM radio band.

        If you get FM interference, you have a really bad case. Could be line interference or direct radiation, since FM is only about 3 meter wavelength (10 feet)

        Obviously it may be in violation of FCC rules....for RFI/EMI........... Nah.. the chinese would never do THAT......

        Does it have an FCC label or a CE label on it anywhere? Maybe not.... Homier is Canada, I don't know off hand the governing authority for EMI in Canada.

        The usual line filter is completely useless at removing RFI/EMI. Some from better companies like Tripp-Lite are made for the purpose.

        Try a good line filter first, one you can plug it into. If that does not help, then you have a problem that will need internal fixing.

        Evan's suggestion isn't bad.... most line conducted EMI is "common mode" and a lot of that can be cut down by wrapping the cord as suggested. At least it will tell you something if it changes anything about the interference. Best case it fixes it enough to deal with.

        I do this stuff for a living.... designing to meet EMI specs. it can be a pain, and the local "suits" don't even want to hear about the whole issue.... let alone some chinese vendor.
        Last edited by J Tiers; 10-02-2006, 06:11 PM.
        1601

        Keep eye on ball.
        Hashim Khan

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        • #5
          If the controller is wiping out the AM band, there's little you can do about it from a regulatory standpoint. I've been thru that painful experience a few years back with a product that operated in that band and AC drives used in commercial laundry rooms in hospitals, nursing homes, etc.

          My own VFD (Hitachi) wipes out the AM band along with all of the evening talk shows, when it is on at any speed. That's when a CD or MP3 player is handy.

          Evan + JT, There is a trick you can do with ferrite stick antennas. You can adjust a trim cap in parallel with it to cause resonance at the station's frequency. This antenna can then be positioned in such a way as to cancel the local source of interference. It needs to be wired across the radio's internal antenna, of course. It's amazing but you can almost eradicate spot interference from nearby TV sets and the like ... even another AM station as long as its in a different direction (phase).

          Den
          Last edited by nheng; 10-02-2006, 08:01 PM.

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          • #6
            My mini-mill(same controller I think) had the brushes arcing because they were stuck in the slots,it screwed with the radios too.I took the brushes out and cleaned up the slots with emery paper on a stick so they would slide in the holders as advertized.Problem solved for me,hope that helps.
            I just need one more tool,just one!

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            • #7
              Originally posted by wierdscience
              My mini-mill(same controller I think) had the brushes arcing because they were stuck in the slots,it screwed with the radios too.I took the brushes out and cleaned up the slots with emery paper on a stick so they would slide in the holders as advertized.Problem solved for me,hope that helps.
              You have a mini lathe?? wow
              Truth be told, down here in Florida, I wish I still had my mini lathe, and micro mill... Better than nothing. Theres steam locomotive plans begging me to make use of them...

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              • #8
                Yea, my 7x10 lathe does the same thing. Makes it hard to listen to Rush! I'm not on it that long though and never tried anything. Mostly just bushings. The brush and comm clean sounds like a good idea. I'll put that on the to-do list. Somewhere around number 2,187.

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                • #9
                  Originally posted by BillH
                  You have a mini lathe?? wow
                  Truth be told, down here in Florida, I wish I still had my mini lathe, and micro mill... Better than nothing. Theres steam locomotive plans begging me to make use of them...
                  Nah,I have a mini-mill.Ya,I know why would guy with a b-port and the run of a full machineshop need a crappy little mini-mill?

                  Simple,I need to make tiny little tedious parts from time to time and it sucks standing infront of full sized machines straining my back and eyes to see the the rat turds as I call them

                  I have to admit,you get a lot of machine for $425.It's rough around the edges,but what else is there?Sherline and Taig are too small and Sherline's accesories are thier's and thier's only.
                  I just need one more tool,just one!

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                  • #10
                    EMI / RFI Reduction

                    As noted, the problem is probably the internal motor speed controller. It works by rapidly switching power on and off to the load to reduce the average voltage to the motor and thereby slow it down. Works very much like a light dimmer, which can also cause the same RFI problems. The best way to reduce the noise is to do a few simple things. 1. enclose the motor controller circuitry in a metal enclosure (a shield). 2. Make sure that the metal enclosure is well grounded. and 3. use some small capacitors located as close to the input and output of the motor controller board as possible (preferably inside the metal enclosure) to bypass the line noise to ground. Locate a friend who is an Amateur Radio Operator and get them to help you locate a copy of one of the several good works on EMI / RFI suppression. It will have detailed help suggestions for this and several other situations.

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                    • #11
                      Mini-lathe causes exteme electrical interference!

                      Yes, chokes and capacitors will do the trick. Grounded metal enclosures will do the trick also. All of the remedies used in conjunction, even better.

                      Any amateur radio supplier will have a good selection of books on RFI/EMI issues. HRO and Amateur Electronics Supply are the two big national suppliers and even have their inventories on line.
                      Jim (KB4IVH)

                      Only fools abuse their tools.

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                      • #12
                        Oh one other thought,on mine the conduit from the controller to the motor is plastic flex conduit with no shielding,maybe try shielding it too.
                        I just need one more tool,just one!

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                        • #13
                          Ther are really only three answers to EMI.

                          1) don't make noise.... slow down switching, change design etc....

                          you can't do that. You are stuck with their design, or you wouldn't be asking about it.

                          Possible if it is a brush type motor that you can do some good.... not the first choice.

                          2) Enclose the offending device effectively....

                          Maybe you can do that, maybe not, depends on your ingenuity, and the basic design.

                          3) Filter out the noise and let only the desired signal (or power) pass.

                          You can do this for the power line, externally, or, if you are ingenious, internally, with a filter available from Digi-key or elsewhere. Rolling your own is possible, but tricky, you can RAISE the noise one place in the process, filter design is not simple.

                          Since It sounds like you are unfamiliar with all this , the external filter is your best starting point.
                          1601

                          Keep eye on ball.
                          Hashim Khan

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                          • #14
                            If you can successfully contain the interference source to the inside of a grounded shield container with proper bypassing, there won't be any RF noise (or very little) on the the main power lines or on the load side. A capacitor will pass alternating current. The trick is to use a capacitor value that will have a high reactance to low frequency AC (Mains Power) and a low reactance to high frequency RF Interference. In effect, the capacitor looks like a very high resistance to low frequencies. That is so you don't blow any fuses. And, it looks like a very low resistance path to high frequencies, therefore "bypassing" the RF noise component to ground. Like skimming the bad old cream (fat) off the top of the milk. Usually, in this application, capacitor values on the order of .01 Microfarads (uF) with a minimum working voltage of 300 to 500 Volts AC will probably get you in the ball park (assuming you have a 120 VAC motor). These can be had small enough to fit in almost anywhere. They are cheap too.

                            Chokes (Inductors) are probably overkill for this application. A choke will pass DC but block AC. Useful, if you have a DC motor that you are controlling. For the most part though, chokes are used in conjunction with capacitors and/or resistors to form filter networks to deal with particular frequency ranges in a desireable way. Takes a bit of (electronic) designing to get it right. Unnecessary finesse in this case. What you are after is cheap brute force. Capacitors alone are good at that.

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                            • #15
                              One thing I forgot to mention and so did everyone else (directly) is to check the machine ground. Make sure the enclosure and the rest of the machine shows less than one ohm to the ground on the outlet.

                              This is easiest to do if you have a spare power cord that you can cut the plug from, leaving a few feet of cord on the plug. Put some wire nuts on the hot and neutral to prevent shorts. Strip the ground bare and clip to it. Plug it into the other outlet on the duplex outlet the machine is connected to (assuming it is, if it isn't you have to get a bit more creative without frying youself).

                              Check your zero on the meter by shorting the leads on the lowest ohms range. It should read less than one ohm although it may not read right on zero. Clip one lead to the bare ground on the cord you prepared. Start probing to various parts of the machine. You should not see more than one ohm higher than whatever the meter showed with the leads shorted.

                              If you have a higher reading than that then you have a grounding problem. This can make the entire machine act as an antenna for RFI. All exposed metal parts of the machine should be electrically connected together and grounded.

                              Another problem that can cause noise is a high resistance in the neutral in the house wiring. These sorts of problems are more common than you may think. What happens then is that the return current may raise the neutral voltage above ground and cause it to radiate. This varies with load and if it exceeds 5 volts ac under a maximum load of 12 amps on a 15 amp 117vac circuit you have a problem. It is measured from neutral to ground at the outlet while a load is placed on the circuit at that outlet. An electric heater makes a good load while measuring at the other socket on the outlet. If the ground pin is on the bottom the left blade is the neutral.

                              If more than 5 volts is measured neutral to ground then the wiring is suspect and needs to be checked.
                              Last edited by Evan; 10-04-2006, 01:01 AM.
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