Small Engineering project - Battery tester

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  • LCHIEN
    Internet Fact Checker
    • Dec 2002
    • 20914
    • Katy, TX, USA.
    • BT3000 vintage 1999

    Small Engineering project - Battery tester

    This is not Finewoodworking.
    Tired of messing with batteries. I have all kinds of voltmeters but they are clumsy to measure everyday primary batteries. When replacing batteries in equipment that stops working I always check the batteries I took out and check the batteries that I put in. Saves me from changing batteries and still nat having a working unit... sometimes the new batteries are bad and sometimes the batteries are NOT the reason it stops working.

    So the problem is that it takes three hands to test a battery. One to hold the meter, one to hold the positive probe and one to hold the negative probe. Oh and another to keep the battery from rolling away. And its ideal to test batteries under load - which means even more things to hold.

    I made this jig from scrap wood, a Harborfreight free DMM, a piece of 14 Ga copper wire cut from a piece of Romex, and some electrical bits and ends.

    I cut a slot, just a bit shallower than the diameter of the copper wire and put it underneath the wood strip on the left.I drilled holes for common battery sizes D, C, AA, AAA.
    I put the copper wire into the slot so it was right under the battery holes. When you place a battery in the hole the negative electrode rests on top of the wire. The wood keeps it from falling over.
    I put the meter on the base plate with Velcro so I can change the battery one day. I routed the copper wire up to the top and connected it to a metal plate (old single edge razor blade, because I couldn't find any brass shim around the house).

    Electrically - I teed the DMM negative lead into the copper wire and the Neg. binding post And the Pos lead to the Pos. binding post.

    Now the negative black terminal is in common with all the battery holes bottom and the razor plate. The red wire is free. The binding posts are in parallel with the meter input.

    I can drop a battery in the hole and measure it with one hand holding the red lead. Or place a button cell on the razor plate and measure the positive electrode.

    And as shown, I can wire a load resistor (in this case a 150 ohm which pulls 100 ma from the battery under test... I can remove it easily.

    So there's a picture of the finished unit, and a little schematic of how its wired. Don't ask for drawings or plans, it was more or less done "on the fly".
    It cost virtually nothing but involved some big forstners, and some grooving and slotting. There's a big dado under the terminals where the wiring is done and hidden.


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    Last edited by LCHIEN; 07-28-2016, 09:53 PM.
    Loring in Katy, TX USA
    If your only tool is a hammer, you tend to treat all problems as if they were nails.
    BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions
  • atgcpaul
    Veteran Member
    • Aug 2003
    • 4055
    • Maryland
    • Grizzly 1023SLX

    #2
    Loring, that's a nice solution. At what voltage to do swap out the battery?

    I've only used a HF coupon to get a free flashlight. I will have to get the free multimeter next time.

    Comment

    • LCHIEN
      Internet Fact Checker
      • Dec 2002
      • 20914
      • Katy, TX, USA.
      • BT3000 vintage 1999

      #3
      Originally posted by atgcpaul
      Loring, that's a nice solution. At what voltage to do swap out the battery?

      I've only used a HF coupon to get a free flashlight. I will have to get the free multimeter next time.
      Unloaded, Usually 1.3V is OK, 1.2 is OK, too, that's the voltage of NiCd and NiMH. But when you get to 1.1V most applications become marginal.
      Rechargeable batteries have a more or less flat discharge voltage of about 1.2 Alakalines have a declining voltage that goes from about 1.5 down to 1.2 when exhausted. A lot of electronics have problems at below 1.1 volts per cell, some analog quartz clocks run to ,.9V
      When you apply a load, they go drop voltage even lower..
      Last edited by LCHIEN; 07-28-2016, 09:22 PM.
      Loring in Katy, TX USA
      If your only tool is a hammer, you tend to treat all problems as if they were nails.
      BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

      Comment

      • leehljp
        Just me
        • Dec 2002
        • 8429
        • Tunica, MS
        • BT3000/3100

        #4
        Great idea. Thanks for posting this info on acceptable voltage too.
        Hank Lee

        Experience is what you get when you don't get what you wanted!

        Comment

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