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RE: [Electronics_101] Re: old ammeter

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  • Rick Sparber
    James, Don t forget that you can run multiple strands in parallel. That will minimize any heating effect and give you very low resistances. One trick I
    Message 1 of 51 , Feb 13, 2013
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      James,

      Don't forget that you can run multiple strands in parallel. That will minimize any heating effect and give you very low resistances.

      One trick I sometimes use is to take a very long piece of the wire and measure its resistance. Say you have 100 inches of wire and measure 10 ohms with your meter. That means 10 inches is 1 ohm so 1 inch is 0.1 ohm.

      Rick

      -----Original Message-----
      From: Electronics_101@yahoogroups.com [mailto:Electronics_101@yahoogroups.com] On Behalf Of james nicholson
      Sent: Wednesday, February 13, 2013 1:07 PM
      To: Electronics_101@yahoogroups.com
      Subject: Re: [Electronics_101] Re: old ammeter

      Rick,
      I have some heating element wire from an old dehumidifier that was also a heater. Possibly I will start big and work my way down till it matches my Fluke meter reading. I am a retired mechanic from a Caterpillar dealership. Worked a lot on 12 & 24 volt heavy equipment systems but not so much on electronics. Thank you , James



      ________________________________
      From: Rick Sparber <rgsparber@...>
      To: Electronics_101@yahoogroups.com
      Sent: Wednesday, February 13, 2013 8:26 AM
      Subject: RE: [Electronics_101] Re: old ammeter



      I make my low resistance shunts out of thin steel wire although heating
      element wire can be used too. The trick is to accurately measure it.

      Rick

      -----Original Message-----
      From: Electronics_101@yahoogroups.com
      [mailto:Electronics_101@yahoogroups.com] On Behalf Of Kerim F
      Sent: Wednesday, February 13, 2013 6:13 AM
      To: Electronics_101@yahoogroups.com
      Subject: [Electronics_101] Re: old ammeter

      --- In Electronics_101@yahoogroups.com, "Nick" wrote:
      >
      > Hi guys, I'm fairly new to electronics and have a question about an old
      ammeter that I acquired. I know that it requires a shunt as the wires on the
      posts are small and it is a 100 amp meter. In the lower right corner of the
      meter face it shows [E.S.=50mv ]. What can I use for a shunt and does it go
      in series with the + or in parallel with the + and -. Will it read full
      scale with the shunt installed [not that I would ever need that much]. Thank
      you in advance for any info.
      >

      In parallel.
      An ammeter is actually a sensitive voltmeter.
      It seems the full scale voltage of your ammeter is 50mV.
      If the the shunt is 1 Ohm, the full sacle current would be 50mA If the the
      shunt is 0.1 Ohm, the full sacle current would be 500mA.
      If the the shunt is 0.01 Ohm, the full sacle current would be 5A.
      If the the shunt is ?? Ohm, the full sacle current would be 100A ;)

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    • Rick Sparber
      In reading the thread, it sounds like you got the help you needed. Rick ... From: Electronics_101@yahoogroups.com [mailto:Electronics_101@yahoogroups.com] On
      Message 51 of 51 , Mar 21 7:18 AM
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        In reading the thread, it sounds like you got the help you needed.

        Rick

        -----Original Message-----
        From: Electronics_101@yahoogroups.com [mailto:Electronics_101@yahoogroups.com] On Behalf Of james nicholson
        Sent: Wednesday, March 20, 2013 1:45 PM
        To: Electronics_101@yahoogroups.com
        Subject: Re: [Electronics_101] Re: old ammeter

        Hi Rick,
        I have another question for you. The control board on our treadmill went out. I have done some tests and the motor is fine. It's a DC 120 volt brush type motor, it has a choke coil in series with the motor. I don't want to spend $120 for a new board unless I have too [ retired & fixed income].I ran the motor with a big ceramic ohmite pot of 68 ohms and then thru a bridge rectifier. The motor ran fine and I could control the speed but the pot got really hot which is understandable because of the iron coil. I found a router speed control on ebay that is good for 120 volt-15 amp--says it is good for any ac or dc motor brush type. What are your thoughts on using this as a speed control. Sent a pic of the motor data plate. Any help would be greatly appreciated Just remember I'm very elementary when it comes to electronics. By the way haven't got to my ammeter shunt yet but will get it.
        Thank you, James
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