Battery Voltage Indicator problem.

Discussion in 'General Electronics Chat' started by bilalbajwa, Mar 24, 2010.

  1. bilalbajwa

    Thread Starter Member

    Feb 21, 2007
    18
    0
    Guys i am trying to build a battery voltage indicator. I googled and built this circuit from this link
    http://www.reuk.co.uk/LM741-OpAmp-Voltage-Indicator.htm

    My circuit is not working as it should. I am just lost. Will anybody pl. suggest some other circuit or modify the same so that it works.

    My goal is to indicate fully charges at 6V and above, max is 8.4V(Green Led). and 4.5V and below is low battery (Red Led).
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    What Zener diode did you use?

    If it's rated for more than about 3.9v, it won't do you much good.

    The 10k resistor is too high for a standard 500mW Zener at the voltage ranges you want to use it.

    You aren't saying what kind of a battery you are dealing with.

    If it's a lead-acid battery, it should be charged at about 1/5th it's AH rating up to around 7v, and then "float charged" at around 6.7v-6.8v. If you let it get down to around 5.7v, it's nearly completely discharged - and they don't last long if you drain them that low.

    If you're using a different kind of battery, your requirements will be different.
     
  3. bilalbajwa

    Thread Starter Member

    Feb 21, 2007
    18
    0
    I am using Duracell Rechargeable Batteries. NiMH. 6 cells.

    I dont have a zener can i use something else? Like a forward biased diode 1n4001.


    What should be the value of 10k resistor.


    Max voltage of my batteries is like 8.4 V (thats is what it charges to when i connect it to 9 volt charger.)
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I thought you said that you built the circuit in the link? :confused:
    If you did not use a Zener diode, then you built something different.

    A single diode won't have enough forward voltage. The 741 will have a really hard time seeing something that close to the negative rail. The 741 really is not the right opamp to use for this, as it needs around 10v to work.
     
  5. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    unfortunately no. The zener is the "cutoff" marker.
     
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