How to monitor 12 Battery with microcontroller?

Discussion in 'General Electronics Chat' started by french_guy, Jun 3, 2013.

  1. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    How can I simply monitor battery voltage (12V deep cycle battery) with a microcontroller that has 0-5V only ADC?
    Well, actually I want to use the microcontroller to monitor the battery voltage and prevent a sump pump to run if the voltage is too low (I don’t want to damage the battery with a too deep discharge….)
    Kind of a low-voltage battery cut-off.......
     
  2. Stuntman

    Active Member

    Mar 28, 2011
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    Google "voltage divider" and see if this guides you to a solution.
     
  3. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    Why can't you use a cheap ebay led or lcd voltage display ????
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Because he would have to check it on a regular basis, he wants to design a system where a Microcontroller to do it for him.
     
  5. absf

    Senior Member

    Dec 29, 2010
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    I would use a LM393 voltage comparator to compare the battery voltage with a reference voltage from TL431. Output from comparator would operate a relay to cut off the battery from the load.

    But if you like to use a micro, I'll pick 12F675 which has an ADC built-in.

    Allen
     
  6. Brownout

    Well-Known Member

    Jan 10, 2012
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    A 12V battery can put out almost 14V when fully charged. Therefore, use a 3:1 or 4:1 divider to make sure you have the voltage down below 5V. You can use a 10K and 3.3K resistro divider, for example. After converting the voltage, multiply the result by 4 to convert it back to the correct voltage.

    I have the exact same project in the works. I want to use a UC to monitor a battery and cut off the load when the battery gets low. But I'm using a 3.3V uC so I need more voltage division. I'm also monitoring the current and calculating the amp-hours. Anyway, you're going in the right direction.
     
  7. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    One thing to realize before it bites you is the battery voltage WILL rise as soon as you turn the pump off... so you need a different, larger voltage to turn it back on.

    Generally it's called hysteresis, which means you want the comparator (or program reading the D2A) to be hysterical.
     
  8. Brownout

    Well-Known Member

    Jan 10, 2012
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    Or else once the uC turns it off, it stays off until manually reset.
     
  9. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    The 12F683 is a newer version of the 12F675, and is supposed to be easier to use.
     
    absf likes this.
  10. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    I was thinking about an Arduino, easy to program.......I don't want to use a uC that programs in assembler
     
  11. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    In that case, the monitoring of the battery should be done when the pump is ON, and not when it's OFF. Thus I will have real voltage measure of the battery under load
     
  12. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    PICs can be programmed in C or basic as well, however there is a learning curve (which I am trying to climb.) PICAXE is another option that you might consider. Here's a discussion that might be interesting. http://www.picaxeforum.co.uk/showthread.php?15960-PICAXE-to-measure-a-12v-Battery
     
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