Using A PIC As A Lead Acid Battery Charger? (Alarm Batt)

Discussion in 'General Electronics Chat' started by ajm113, Jan 7, 2012.

  1. ajm113

    Thread Starter Member

    Feb 19, 2011
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    5
    I've attached a schematic and a program plan on this scratch image. I'm hopping to accomplish a lead acid battery charger for alarm batteries for this backup power supply I hope to use to supply enough power to recharge 5 cell phones ... or keep them alive... I'm going to be use 2 batteries of course, so I wanted to start small and work my way up and master being able to charge one battery.

    I'm wondering if using a PIC would do the job just fine using two voltage regulators to control the amps to feed the battery so I can easily tickle charge it if I wish.

    If you read the schematic and program plan, I basically have the rectangles as functions and the diamonds as if statements. If you look to the right you notice a loop I've designed to trigger after every function the PIC does to insure the battery doesn't over charge.

    I was wondering if my schematic/program sounds good and if I can get some tips or pointers on a much more efficient design.

    Schematic Notes:
    I forgot to put in a voltage regulator that sets the volts to 14v instead of 25v.
    The program plan should say 14v instead of 13v.
    The poorly drawn N-Channel MOSFET should be the two voltage regulators.

    Thanks, Ajm.

    P.S Sorry for the poorly drawn image, it's 3 AM.
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    718
    I can't really read your schematic, or understand your block diagram.

    Are you charging phones or car batteries? Charging voltage is usually 13.8V or higher.

    There are ready made Charge Supervisor ICs with the optimal Lead-Acid profile stored in them.

    Maybe take a look at the datasheet to get ideas?
     
  3. ajm113

    Thread Starter Member

    Feb 19, 2011
    176
    5
    Well what I'm doing is trying to charge a 12V 7ah lead acid alarm system battery so I can use it as a backup power supply to charge 2-3 cell phones when the power goes out. Most of the batteries I've found actually require 14v to charge. I've heard from a alarm system tech saying that these batteries are non rechargeable...

    Even most of them and their documentation says they are and how to charge them. I'm guesting by the looks of the documentation it would be able to solve my problem? I was kinda hopping to use a PIC, but if a IC is able to do the job much better and cause less damage then experimenting. It may save me some money in the long run then.
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    You could go either way, you could program a PIC to do about the same thing with a few more external components, the datasheet has enough info to replicate it.


    If it is a grey block battery and is lead acid, with two spade connectors on top, it's a gel cel or AGM rechargeable 99 times out of 100.
     
  5. ajm113

    Thread Starter Member

    Feb 19, 2011
    176
    5
    Ah, so that's the word for them, makes much more sense now.

    From your opinion and or experience, would you say a Lithium battery would be a better option for this case? If all I was using to do is charge cell phones and a circuit that was maybe not consuming more then 3v-5v and 300ma - 500ma? I was thinking of adding a counter/sensing unit to determine if a cell phone maybe fully charged to save energy when it's using the backup power.

    I was thinking of this because they seem to last longer in recharges, plus the power required isn't going to use as much energy such as a alarm system anyways.
     
  6. russ_hensel

    Well-Known Member

    Jan 11, 2009
    818
    47
    Pic is great ( arduino is easier ). I think you need a transistor to boost, control the charge current. Using a tranistor ( darlington, mosfet or other high current gain ) with an op amp for a constant current circuit is good for charging many batteries. Switching from constant current to constant voltage at then end of charge is a common technique. With a pic you can change the program to charge different types of batteries. Google will take you to a lot of material, I am not going to try to describe it all here.
     
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Cell phones have the charge control circuitry built in, so determining when it is fully charged should be simply by detecting a large drop in current use. Many phones will leave the screen lit up when plugged in, even after fully charged, but that isn't much current compared to the high draw of charging.
     
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