Need help for lead acid battery charger

Discussion in 'The Projects Forum' started by embpic, Jun 11, 2014.

  1. embpic

    Thread Starter Member

    May 29, 2013
    187
    3
    i am doing charging circuit for lead acid battery of 12 volt and 1.2Amp Hrs.i came across that there is two types
    of method to charge battery. so after reading i decided to use switch mode charging method.
    after serach i got BQ24450,UC3909,UC3906,bq34z110 ic's which is related to this.

    so which ic is reliable and cost effective??
    and also have basic question is, what is cell in battery??
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Do you have experience in making PCB for SMPS.

    A lead acid consists of 6 cells of 2.2V each at full charge giving a total of 13.2V at the battery terminal.
     
  3. embpic

    Thread Starter Member

    May 29, 2013
    187
    3
  4. embpic

    Thread Starter Member

    May 29, 2013
    187
    3
    i ahve uploaded image
     
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    SMPS ain't Analog. Well somewhat but not complete.

    To make a SMPS u need to know how to wind the SMPS transformer.
    Can you do it ?

    If you can't u need a linear front end with a switch mode back end.
     
  6. Lauri1991

    New Member

    Oct 20, 2013
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    0
    I've attached an image with this post. I want to calculate battery model capacitance. I need to charge battery but I want to simulate it in MultiSim 12.
    I've made some calculation there but I don't know if they are right. Can someone help me? Explain a little perhaps.
    Thnx.
     
  7. crutschow

    Expert

    Mar 14, 2008
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    Please don't hijack threads. Start your own and I'll try to answer your question.
     
  8. crutschow

    Expert

    Mar 14, 2008
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    For such a small battery and charging current I don't see the need for the added complexity of a switching regulator unless you are really concerned about charging efficiency.
     
  9. Metalmann

    Active Member

    Dec 8, 2012
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    Here's an interactive video explaining SLA batteries, that I posted a few days ago:


    http://www.batterystuff.com/tutorial-interactive-battery.html


    It helped me understand them a little better.;)
     
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Agreed! Similar 12v 1.2Ah batteries are used in alarm system etc and they just constant charge them with a LM317 set to be a 13.8v voltage regulator.

    You don't even need a series resistor etc when charging because the battery internal resistance is quite high, they never reach the 1.8A internal current limit of the LM317.
     
  11. embpic

    Thread Starter Member

    May 29, 2013
    187
    3
    If i give 12.8 volt to battery then will it work. will it get charged.
    i am looking for safety purpose. and some indication of low battery and full charged battery likewise.
     
  12. embpic

    Thread Starter Member

    May 29, 2013
    187
    3
  13. wayneh

    Expert

    Sep 9, 2010
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    I believe that would work, although I've never built it. It's a constant-current charge strategy, so it is important that the current it supplies is not too much for the battery.

    There is nothing to slow it down once the battery is charged. A lead-acid battery can tolerate a trickle, but don't over do it.
     
  14. crutschow

    Expert

    Mar 14, 2008
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    That circuit should work but the circuit description is incorrect. You select the value of R1 to control the maximum charging current (≈0.7 / R1), not adjust R5. R5 sets the cutoff voltage at which point the charging current reduces to a low level charge. That voltage should be around 13.8V depending upon the type of lead-acid battery (adjust voltage with no load).

    The maximum charging current should be about 1/10th of the battery ampere-hour (Ah) rating, not what current the battery can "give".
     
    Last edited: Jun 14, 2014
  15. embpic

    Thread Starter Member

    May 29, 2013
    187
    3
    Thank you sir
    But the charging current should be low, right??
    and i also need some indicator so i can get to know charging state and charging status.
     
  16. crutschow

    Expert

    Mar 14, 2008
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    The charging current should be no more than 1/10th of the battery's Ah rating. It can be less.

    If you just want a couple of LED indicators then use comparators, one to detect the voltage across a small series resistor in the ground connection to detect charging current and one to detect when the battery voltage has reached the desired fully charged value. You can use a zener or voltage reference IC to establish the trigger points for the comparators.
     
    Last edited: Jun 16, 2014
  17. embpic

    Thread Starter Member

    May 29, 2013
    187
    3
    hello sir as per this configuration i found circuit as
    [​IMG]

    i found this circuit common. so, will it charge the battery??
     
  18. MrAl

    Well-Known Member

    Jun 17, 2014
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    490
    Hi,

    A simpler alternate method to get the capacitance is:
    C=I*dt/dv

    where I is the current in Amperes, dt is the time in seconds, and dv is the discharge over the full discharge range.

    For your example, we can set I=80 for "80AHrs" and then dt=3600 which is the number of seconds in one hour, and the discharge voltage is 12.7-10.5=2.2 volts. Using that equation we get:
    Ceqiv=130909 Farads

    You should probably have started your own thread for this question though.
     
  19. wayneh

    Expert

    Sep 9, 2010
    12,120
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    The input label is incorrect. It needs an input at least about 3V higher than the battery voltage, so ≥16V. And the LM317 is rated to, I think, only 37V, not 40V as shown.

    Also, it shows 1A supply. The BC140 transistor will not conduct until its base sees ~0.6V or more. As shown, the current across the 0.51Ω shunt resistor would need to exceed 1A for that to happen. So this current control scheme wouldn't actually be doing anything with that supply. That's OK.

    Otherwise, that should give you a constant voltage supply with a current limiter, and that's a common strategy for charging a lead acid battery. I would drop the voltage to 13.8V though, so it can be left connected as a trickle charger.

    It's worth noting that the LM317 will limit it's own current to a degree, to protect itself against overheat. If you supply it with high voltage, over 20V or so, it will be limited by heat dissipation. The current limiter transistor won't help.
     
    Last edited: Jun 17, 2014
  20. MikeML

    AAC Fanatic!

    Oct 2, 2009
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