How do I use a multimeter to test the charge of NIMH batteries?

Discussion in 'Off Topic' started by timswim78, Sep 17, 2006.

  1. timswim78

    timswim78 Diamond Member

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    I got a free multimeter with no instruction manual. I would like to use it to measure the mAh of my rechargeable AA and AAA batteries. However, I'm not sure what settings to use. I would appreciate any help. Here is a photo of the multimeter.

    http://bibo.us/cl/meter.jpg

     
  2. dighn

    dighn Lifer

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    it's not something you can measure with a multimeter easily. you could try looking up the voltage vs charge characteristics of a nimh battery but then different battires probably have different characteristics
     
  3. timswim78

    timswim78 Diamond Member

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    Bummer. I guess that I can use my BC-900 charger to do this, but I was looking for something a little faster.
     
  4. Eli

    Eli Super Moderator<br>Elite Member
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    You can't measure amperage over time with your average DMM.

    Edit: Well, you could.. but you would be measuring the time vs. amperage aspect and doing the calculations.
     
  5. timswim78

    timswim78 Diamond Member

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    Thanks for the replies Eli and dighn. So, how does one measure the "charge" of nimh batteries?
     
  6. Eli

    Eli Super Moderator<br>Elite Member
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    The only real practical way is to use one of the fancy chargers available now.
     
  7. timswim78

    timswim78 Diamond Member

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    OK, well I've got this one. It tests batteries, but it is a slow process.
    http://www.bestfoto.com/Product%20Reviews/product%20review02.htm
     
  8. jadinolf

    jadinolf Lifer

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    :thumbsup:
     
  9. Eli

    Eli Super Moderator<br>Elite Member
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    Yes. You have to actually discharge the battery to measure its capacity, obviously.

    It's probably only a 200mA load to test or something.
     
  10. Jeff7

    Jeff7 Lifer

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    Get a Triton battery charger (or a TritonII), set it to discharge at whatever rate you want, and it'll discharge the battery until it reaches X volts. I think 1.0V/cell is considered "dead" for NiMH, though it may be 0.8V, I don't remember.
    It'll record how many mAh your battery has.

    It also costs around $100. :Q

    It's a damn capable charger though. The only thing I don't like is that it can't charge multiple individual cells. By that I mean this:
    While it can charge several individual cells at a time, it does so when they're arranged in series: the entire collection is charged as a single battery, so each cell doesn't receive individual treatment from the charger. For that, you'd need a charger with independent charging circuits. I've got this Ansmann charger on the way. With that, I should be able to deliver a good charge to damn near any battery in existence. :D
     
  11. 0roo0roo

    0roo0roo No Lifer

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    what? no bounce test? drop em off a 20 story building. the more bounce, the more energy!
     
  12. So

    So Lifer

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    Why in gods name would you spend so much to charge batteries!?!?!
     
  13. 0roo0roo

    0roo0roo No Lifer

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    some people are anal.
     
  14. her209

    her209 No Lifer

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    Easiest way is to turn the dial to ACV 200 and put each probe into the AC outlet.
     
  15. Oblivionaire

    Oblivionaire Senior member

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    If you want to use the multimeter you're going to have to put the battery under load. Given V=IR, R=V/I, if you want to draw lets say 500ma, that would be 1.5v/.5A=3ohms, so you'll need a 3 ohm resistor. Using some simple math I'm sure you can figure out how to calculate maH from that. Halve the resistor value of you want to draw 1A, double it if you want to draw 250ma.
     
  16. Jeff7

    Jeff7 Lifer

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    Because I've lost batteries to cheap quick chargers that force-feed whatever they're given, to the point that I sometimes get less than 50 recharges.
     
  17. Rubycon

    Rubycon Madame President

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    Not just that - the more sensitive chemistries (namely Lithium Poly) can rupture and catch fire in a blink with a poorly designed charger!
     
  18. Jeff7

    Jeff7 Lifer

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    That's the sort of thing which worries me these days - potentially flammable batteries in a culture of "Make it as cheap as possible. Cut corners when possible." Li-ion/poly batteries, as I understand it, are things where you really don't want to follow that philosophy. Anything that can create a fire is something that you don't want to go cheap on.