Battery ma-h test circuit help.

Discussion in 'The Projects Forum' started by emilj726, Jun 10, 2016.

  1. emilj726

    Thread Starter Active Member

    Oct 1, 2010
    52
    2
    I designed the current sinking circuit to test out a bunch of these 3V Lithium coin cell batteries that I have.
    The battery is rated for 620mA-h.
    I built my circuit and for the life of me I cannot get it to work. I am not even getting the 6.2V drop on pin 3 of the mosfet.
    Can anyone help
     
  2. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    Your battery voltage is only 3 volts.
     
  3. emilj726

    Thread Starter Active Member

    Oct 1, 2010
    52
    2
    I can make the voltage divider give 1V hence, 100 mA.
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    You're never going to get 6.2v from a 3v battery...lower the voltage divider reference to get 1.5v or less...
     
  5. emilj726

    Thread Starter Active Member

    Oct 1, 2010
    52
    2
    I didn't think this right. In my head i kept thinking because pin 3 is 6.2V that will make pin 2 6.2V.
    But the feedback is the op-amp driving the output hard to get inputs the same.
    I think i answered my own question.

    I got the circuit to work with the modifications that I have attached. I am running 100 mA into the battery.
    I guess how will I know when the battery is depleted?
    What voltage will be across The battery when the circuit is on?

    Well the battery just blew up. is the - of battery supposed to be connected to Drain of mosfet or the +?
     
    Last edited by a moderator: Jun 11, 2016
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    The battery will discharge down to 1v approx, at switch on it will be 3v.

    The battery positive is to the Drain, the Negative to the source.
     
  7. emilj726

    Thread Starter Active Member

    Oct 1, 2010
    52
    2
    I am not sure why it blew up???
     
  8. Roderick Young

    Member

    Feb 22, 2015
    408
    168
    100 mA is a high demand to put on a coin cell already, that may be what's blowing up your battery. Have you measured the actual current with a DVM? Could it be more than you expect?
     
  9. emilj726

    Thread Starter Active Member

    Oct 1, 2010
    52
    2
    well I set the Current limit on the 9V power supply to 200 mA. What's odd is when I was measuring voltage from Drain to ground I was getting like 7V. I thought that was strange.
     
  10. BobTPH

    Active Member

    Jun 5, 2013
    782
    114
    Um, is everyone else seeing a posted circuit that I am not seeing?

    Bob
     
  11. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    Yes, it was a pdf, must have deleted it.
     
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