How to measure AMP battery

Discussion in 'General Electronics Chat' started by sendbad, Mar 13, 2015.

  1. sendbad

    Thread Starter Member

    Jan 8, 2015
    43
    1
    hi
    i have a lithium battery 3,7 volt
    Unknown number amps
    How can i know her ah number

    or her amper
    thank you
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,179
    1,800
    Discharge the battery into a known load, then measure the current and the time.
     
  3. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,003
    745
    have you got a picture of the battery?
     
    Roderick Young likes this.
  4. sendbad

    Thread Starter Member

    Jan 8, 2015
    43
    1
    when i measure the current using mulltimetr not gev me Fixed number
    Different numbers and then disappear
     
  5. MrChips

    Moderator

    Oct 2, 2009
    12,452
    3,371
    What is the resistance value of your load?
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    I'll bet you are shorting the battery by connecting the ammeter across it without a series load resistor....
     
  7. sendbad

    Thread Starter Member

    Jan 8, 2015
    43
    1
    Does not have data
    just 3,7 volt

    [​IMG]
     
  8. Papabravo

    Expert

    Feb 24, 2006
    10,179
    1,800
    Then Ohms law tells me that you do not have a FIXED and CONSTANT load. An ammeter is a very low resistance, and could be damaged by doing what you did. Pick a resistor that will give you say 50 milliamps.

    3.7 Volts / .050 Amperes ≈ 75 Ohms

    The ammeter in series with the resistor goes across the battery terminals. Just to be extra safe estimate the power dissipated by the resistor as

    (.050 Amperes)^2 * 75 Ohms ≈ 187.5 milliwats

    So a quarter watt resistor will get warm but not explode.
     
  9. sendbad

    Thread Starter Member

    Jan 8, 2015
    43
    1
    resistance value 20 om
     
  10. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,003
    745
    what is the number on the battery
    ?
     
  11. sendbad

    Thread Starter Member

    Jan 8, 2015
    43
    1
    series load resistor 20 om shorting the battery

    so what Suitable om using
     
  12. sendbad

    Thread Starter Member

    Jan 8, 2015
    43
    1
    l
    li-ion 18490 3.7 v
    jo1.f18490ro4 340 13 12

    thes all data in battry
     
  13. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,003
    745
  14. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    I'm guessing that size is about 1500mAh.
    If 20Ω (180mA load current) pulls that battery down immediately, then it is totally discharged, and needs charging before you do any more tests.
     
  15. sendbad

    Thread Starter Member

    Jan 8, 2015
    43
    1
    i will do it
     
  16. sendbad

    Thread Starter Member

    Jan 8, 2015
    43
    1
  17. sendbad

    Thread Starter Member

    Jan 8, 2015
    43
    1
    i will do it thank you
     
Loading...