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R.S. Pot, low resistance for initial rotation.

Discussion in 'Electronic Basics' started by Computer Prog, Jan 12, 2004.

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  1. I bought a RadioShack 5K Linear taper pot for an adjustable power
    supply I built. The pot has about 300 degrees of rotation. I
    connected the wiper with one of the side terminals and I use the wiper
    and the other side terminal to get the resistance. My setup allows me
    to get increased resistance with clockwise rotation.

    The problem is the first 40 degress or so of rotation stays at 1 ohm.
    It then jumps to about 8 ohms and then gradually gets up to 5k. The
    first 40 degrees of rotation are basically useless.

    Is this typical of a pot?
     
  2. Not good ones.
     
  3. CFoley1064

    CFoley1064 Guest

    I bought a RadioShack 5K Linear taper pot for an adjustable power
    Nope. I would guess you got a clunker -- take it back with the receipt for a
    cheerful refund.

    Good luck
    Chris
     
  4. I already trimmed the length of the shaft and I also soldered onto the
    terminals. I doubt my part qualifies for a return. I'll buy another
    and take readings off it before I install it. If it reads the same
    I'll bring it back.
     
  5. How did you cut the shaft? If you put the pot's body in a vice and
    sawed it off, you damaged the pot.

    You have to clamp the shaft, and make sure any opening is covered to
    keep the metal dust out while you cut the shaft.

    --
    We now return you to our normally scheduled programming.

    Take a look at this little cutie! ;-)
    http://home.earthlink.net/~mike.terrell/photos.html

    Michael A. Terrell
    Central Florida
     
  6. I quickly cut if off with an air cut-off tool while the pot was
    mounted in my power supply case. I am not sure how I could have
    damaged it since the cut only took about 3 seconds. I'll try to blow
    it out with compressed air.
     
  7. I took the back off the Pot and this behavior is by design. The
    "resistor" area of the outer terminals does not start until about 30
    degrees of clockwise rotation. In other words, when it starts in the
    fully counter-clockwise position the first 30 degrees of clockwise
    rotation has a metal connection under the wiper that looks like a
    direct connection. The "resistor" starts after that and only runs for
    about 225 degrees of rotation.

    IMO a very poor design.
     
  8. Colubris

    Colubris Guest

    I wonder if the cutting off of the shaft may have over-torqued the
    shaft and damaged one of the stops - allowing excessive rotation. I've
    used quite a few RS POTs - and while not high quality - they've not
    been that bad.

    Arch
     
  9. I wonder if the cutting off of the shaft may have
    No, the shaft and the stops are all undamaged. This is the way the
    POT was designed. I even went back to the store and popped the back
    off a brand new one and I saw the same thing. The first 30 or so
    degrees of clockwise rotation was no resistance under the wiper.
     
  10. Could it be a design that at some earlier time had a power switch on
    the end of the pot? That 30 degree rotation would be about right to
    actuate the switch without raising the volume prematurely.

    GG
     
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