Help on designing a Battery Monitor

Discussion in 'The Projects Forum' started by lloydi12345, Dec 29, 2010.

  1. lloydi12345

    Thread Starter Member

    Aug 15, 2010
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    Hello again, I would like to ask for help about designing my battery monitor on our project. I have searched on the net and I have seen others using LM3914 I.C.. I've seen also battery monitor made from LM324.

    http://www.ikalogic.com/shm_batt_monitor.php

    Would this circuit having LM324 be enough for battery monitoring or LM3914 is better? Our project is a mobile car and it should have a battery monitor on it. We are planning to use 4 rechargeable AA batteries to power the circuit and at the same time power the motors. We will be connecting the battery monitor to the batteries then the indicator wire will be connected to one of the PIC's pins. If you have any other suggestions I would be glad to know them.

    Regards,

    Lloydi12345
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    The 324 circuit would be more than sufficient to signal your controller

    The important thing is the reference voltage, which must not be affected by any changes happening in the battery circuit.

    For a six volt system. a 3 volt or 3.3 volt reference would be a good one. A small (TO92) case voltage regulator could source a reference voltage for you. Or you could use one of the three leg precision voltage reference IC's available. 2.5 volts is a common value for those things I believe.

    http://cds.linear.com/docs/Application Note/an42.pdf
     
  3. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Last edited: Dec 29, 2010
  4. lloydi12345

    Thread Starter Member

    Aug 15, 2010
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    Thank you Kermit2 and iONic for the replies.

    iONic, the link you've posted above is not working :(

    I would like to specify my battery monitor's main purpose. If the battery (maybe the motors' batteries) reaches 1/3 of it's full voltage then it will send a signal to the PIC microcontroller that the battery needs to be charged. I think it's wrong for me to call it battery monitor right? but just a low power indicator.

    Kermit2 I've read the link you've posted. Are they voltage regulators like 7805 IC's? I'm sorry if I can't understand them all fully since I'm not really good at electronics (yet :)).

    Until now I'm still having problem with the design of the project if I'll have 4 AA batteries for the motor and 9v regulated to 5v to power the circuit or just a single battery source which is 4 AA batteries to power both circuit and motor. Since you're saying that I should have different power source (in what I have understood above), I think having two battery sources will be good for me to have a good reference voltage. Would this be right? Or anything else is better? :confused:
     
    Last edited: Dec 29, 2010
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Either way you want to go is doable. There are different advantages to the different schemes. With one battery, you charge more often. with a battery for motor and one for the circuit, you can use a bigger battery for the motor and the charging is less often.

    The voltage reference devices, are very simple. As long as they have a supply of current they will provide a steady reference voltage. You compare this to a fraction of your battery voltage and when the reference becomes bigger than the battery sample the comparator changes outputs and provides you with a signal or other output.


    To alert you to a level of 4 volts you would set the voltage divider to have exactly 2.5 volts with an input from the battery of 4 volts. The output of the voltage divider is compared with reference source and the comparator will output a voltage ( let's say its 4.5 volts when the battery is low) So most of the time the circuit operates, the battery voltage will be around 6 volts and the output from the voltage divider will be approx. 3.5 volts. The comparator output will be low, until the battery gets down below 4 volts. Then the voltage divider sends a lower voltage than the reference voltage to the comparator and it switches output to 4.5 volts.

    This voltage then activates a transistor to light an LED, or powers off the circuit so the battery is not over discharged.

    Does that sound like what you want?
     
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
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  7. lloydi12345

    Thread Starter Member

    Aug 15, 2010
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  8. lloydi12345

    Thread Starter Member

    Aug 15, 2010
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    Yeah it is! Can I ask a simple schematic if I'm not taking much of your time? :)
     
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