[Help] [Arduino] Calculating lithium ion battery capacity[mAh]

Discussion in 'The Projects Forum' started by Diogo Ferreira, Aug 6, 2016.

  1. Diogo Ferreira

    Thread Starter New Member

    Aug 6, 2016
    3
    0
    Hello there im new on this forum and i wanted to ask for help in a project of mine, i'm trying to calculate a lithium ion batery capacity with a arduino. The idea is to use a drain circuit in order to discharge the battery and calculate it's capacity.

    I have a schematic for my project down here but i have a problem, MATH...
    I need to know the math behind mAh of a battery if anyone knows plz tell me i'm stuck here for a time and i can't find any good explanations in google

    Thanks everybody
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,142
    1,790
    It's not math, it is arithmetic. Capacity is the product of current and time, or milliamperes times hours. You should remember that it is unwise to discharge a Lithium battery all the way. When fully charged they measure about 3.8 volts. By the time they get to 3.0 V they are ready to fall of a cliff. Check out Battery University for an in depth discussion of the discharge characteristics. The discharge rate should be about 0.1 times the maximum charging rate.
     
  3. Diogo Ferreira

    Thread Starter New Member

    Aug 6, 2016
    3
    0
    My first project was to make a power bank for my phone using lithium ion battery's 18650 e bought a step up and step down for charging and discharging the batterys but then i got the idea of testing batterys bought in ebay because of scams about true and false mah

    Can you please advise me on what should i do to discharge and measure the batterys, I'm using a 3.5 ohm 10w resistor(just to be sure :) ) and 2.2 ohm mosfet plus the 18650 battery

    At maximum voltage i have less than 1 amp on the resistor

    is this ok ? can you explain me a bit more about that 0.1 times the maximum charging rate?
     
  4. Papabravo

    Expert

    Feb 24, 2006
    10,142
    1,790
  5. Diogo Ferreira

    Thread Starter New Member

    Aug 6, 2016
    3
    0
    I'll be reading it tomorrow :) thanks
     
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