100ma analog ammeter violent at in rush

Discussion in 'The Projects Forum' started by crumpter, Feb 2, 2013.

  1. crumpter

    Thread Starter New Member

    Feb 2, 2013
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    Hello all,
    Newbie here. I am working on a project that requires an analog ammeter to monitor the current draw on a dc motor. The 100 mA DC meter is fine when the motor is running at any of its controlled speeds, typically reading about 10-12 mA, but chatters violently during the in rush at start up, and also when powering down.
    Is this the nature of the beast when monitoring these levels, or is there something I can do to prevent this?

    Thanks,
    Crumpter
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
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    Starting current of your motor will be much higher than normal running current. If you load the motor, current will go up. Do you know the internal resistance of your meter?
     
  3. crumpter

    Thread Starter New Member

    Feb 2, 2013
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    Hi,
    Thanks for the reply. I don't know the internal resistance. It's a cheapo Hopesun panel meter #AIM60100. It just doesn't look like it will withstand too many power cycles like this. Is there a way to dampen its response?

    Thanks Again
     
  4. BillB3857

    Senior Member

    Feb 28, 2009
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    You could place a large cap in parallel with the terminals. Be sure to observe polarity on any electrolytic cap you use. Also be aware that it will slow ALL responses to current changes.
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    I'll second that!

    I have a heap of ammeters with 2200uF caps across their terminals. :)
     
  6. crumpter

    Thread Starter New Member

    Feb 2, 2013
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    Any idea what size cap would help the situation?
     
  7. crumpter

    Thread Starter New Member

    Feb 2, 2013
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    Thanks Bill and RB,
    That last reply overlapped. I'll try the 2200uf and let you know what happens.
     
  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    I use 2200uF but most of the meters were 2A or 5A types.

    A 100mA meter could use a smaller cap in the 100uF-470uF range, depending how much you want to damp those peak movements.
     
  9. crumpter

    Thread Starter New Member

    Feb 2, 2013
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    Thanks again RB. I'll try out something in that range instead.
     
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