Problem while measuring the current of batteries ( they get hot)

Discussion in 'Power Electronics' started by Snowfish, Aug 23, 2017.

  1. Snowfish

    Thread Starter Member

    May 11, 2017
    42
    1
    Hi

    I need a circuit with 6V supply. That is why I connected these 4 batteries (1.5 v) together as in the attached picture. When I measure the voltage, it gives me 6 V. However, the problem is when I am measuring the current, the batteries get very hot after keeping the probes as on this picture (measure.png) for about 30 seconds and when keeping them for some longer time, I heard some cooking sound like ''it's about to explode soon'' and I removed the probes fast because I was afraid that the batteries would explode . I am sure that I connected the batterie's polarities - and + the right way and on the multimeter, I placed the cursor on 10A for the measurement.

    I would like to know if you know why the batteries have that behavior when we measure the current?
    Is that behavior normal and if everything is ok with my way of measurement ?

    Thank you
     
    Last edited: Aug 23, 2017
  2. dl324

    AAC Fanatic!

    Mar 30, 2015
    6,954
    1,609
    How much current are you trying to draw?

    What is the battery capacity?
     
    Snowfish likes this.
  3. phranzdan

    Member

    Aug 4, 2017
    40
    3
    Hi Snowfish: You haven't told us what load is connected to the batteries i.e. what does the rest of your circuit look like. It sounds to me like a direct short across the batteries. The batteries should not get hot under normal load conditions.
     
    Last edited by a moderator: Aug 24, 2017
  4. Snowfish

    Thread Starter Member

    May 11, 2017
    42
    1
    For now, the load is just the multimeter. There is no rest of the circuit, but only multimeter for now. This happened when I had the multimeter connected and I didn't test yet with the circuit.
    It gives me 3.5 A and the circuit will need 1A.
    Now, the batteries are 1.4 V

    Do you think that it's because I havent connected the batteries to the circuit yet and because my only load is the multimeter?

    Thank you
     
  5. WBahn

    Moderator

    Mar 31, 2012
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    You are shorting out the batteries (the multimeter, when configured to measure current, ideally has zero resistance, although in practice it has a some resistance, but not a lot).

    You can easily blow the fuse in your meter or, since most 10 A ranges are unfused, possibly even damage your meter. The current is being limited primarily by the internal resistance of the batteries.

    You got lucky. If you were to attempt this measurement with a car battery it is very likely that you would weld your probes to the contacts and then it would be a race between how quickly your meter could let out enough of its magic smoke to open the circuit, how quickly your wires could melt, or how quickly the car battery could explode.

    Even if you manage not to damage anything, you will quickly drain from the batteries.
     
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  6. dl324

    AAC Fanatic!

    Mar 30, 2015
    6,954
    1,609
    If you expect your circuit to operate for more than a couple hours, you need a higher capacity battery.

    As mentioned by others; you're lucky the batteries didn't explode or blow a fuse in your multimeter.
     
    Snowfish likes this.
  7. WBahn

    Moderator

    Mar 31, 2012
    22,862
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    A rule of thumb is that alkaline AA batteries have about 2500 mAh of capacity. The higher the current draw, the lower the realizable capacity. So if you are drawing 1 A, you can probably expect your batteries to last only a couple hours, possibly noticeably less.
     
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  8. Snowfish

    Thread Starter Member

    May 11, 2017
    42
    1

    Thanks!
     
  9. Jazz2C

    Member

    May 27, 2016
    52
    36
    You shouldn't short the batteries out through the DMM! Bad move!:eek:
     
  10. Sensacell

    Moderator

    Jun 19, 2012
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    Never do this again!
    You just don't "measure the current of a battery" - it's a sure way to blow up both the batteries and your meter.
     
  11. BobTPH

    Senior Member

    Jun 5, 2013
    1,182
    234
    In addition to what others have said, measuring the max current of a battery is meaningless. A fresh battery might produce 10A, but it will fall significantly over just minutes. It is no indication of what you can draw for, say, an hour.


    Bob
     
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