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  1. #1
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    pwm battery charger

    Hi
    I am making a battery charger for charging 2 NiMh cell(esch of 2500mah).
    I used 16f876a and LM317.I am using pwm to switch on and off LM317.
    I didnt use the pwm module inside pic.I implemented it in software beacause
    i want to port the code in to a low cost pic which doesnt have pwm inside.

    Now... I have some doubts..Since i used 2 cells,what voltage level i need
    to set for LM317 output?
    I set it as 9v.When Lm317 is turned on then 560ma current flows through 2 cells.
    Can i accept this value?

    About pwm...
    Whats period i need to set?I set it as 4ms.Duty cyle time is varied according to
    the charging current.With 4ms period LM317 becomes extremely hot.Can I avoid heating of the IC by adjusting the period?
    Can I accept this 4ms period?

    How to determine that battery is fully charged?

    2cells.. means1.25x2=2.50v..I heard that fully charged 2cells maintain 3.96v across across it.Is that currect?
    I am using buit in a2d to check the voltage.I heard about dv/dt checkig of battery..Whats meant by that?How check dv/dt?

    Regards

  2. #2
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    pwm charger

    Can anybody give me answers regarding my design?.......


    Regards


    1 members found this post helpful.

    •   Alt8th December 2007, 17:32

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    pic battery charger

    Quote Originally Posted by sajeev
    Now... I have some doubts..Since i used 2 cells,what voltage level i need to set for LM317 output?
    I set it as 9v.When Lm317 is turned on then 560ma current flows through 2 cells.
    Can i accept this value?
    Nicad, Nimh batteries have to be charged by constant current and not constant voltage. Here is an excellent article about battery charging.

    http://www.angelfire.com/electronic/hayles/charge1.html
    About pwm...
    Whats period i need to set?I set it as 4ms.Duty cyle time is varied according to
    the charging current.With 4ms period LM317 becomes extremely hot.Can I avoid heating of the IC by adjusting the period?
    Can I accept this 4ms period?
    No need of PWM. Charge for 1 second, give a gap of 5 mS and then continue.
    How to determine that battery is fully charged?
    When the voltage starts dropping. It is called negative delta V method.
    2cells.. means1.25x2=2.50v..I heard that fully charged 2cells maintain 3.96v across across it.Is that currect?
    I am using buit in a2d to check the voltage.I heard about dv/dt checkig of battery..Whats meant by that?How check dv/dt?
    dV = previous voltage - present voltage = negative or zero, keep charging.
    dV = previous voltage - present voltage = positive, terminate charge.

    Google for negative delta V and you will come up with many results.

    Cheers

    Ravi



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    lm317 pwm

    I am charging my nimh battery wid a transformer circuit which i m using for my power supply for the application.
    If u want i may send u the circuit.
    I traced the circuit from a universal battery charger. battery charger



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    pwm lm317

    There are many ways to charge Nicad and Nimh batteries. Trickle charge for 14 hours, fast charge in 1 hour or medium charge in a couple of hours.

    If you charge these batteries without monitoring the charge or temperature, you will destroy the battery.

    Cheap chargers will destroy the batteries over a period of time.

    Cheers

    Ravi



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    pwm charger circuit




    •   Alt9th December 2007, 11:14

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  7. #7
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    hi-tech c pwm

    Quote Originally Posted by ravimarcus
    Quote Originally Posted by sajeev
    Now... I have some doubts..Since i used 2 cells,what voltage level i need to set for LM317 output?
    I set it as 9v.When Lm317 is turned on then 560ma current flows through 2 cells.
    Can i accept this value?
    Nicad, Nimh batteries have to be charged by constant current and not constant voltage. Here is an excellent article about battery charging.

    http://www.angelfire.com/electronic/hayles/charge1.html
    About pwm...
    Whats period i need to set?I set it as 4ms.Duty cyle time is varied according to
    the charging current.With 4ms period LM317 becomes extremely hot.Can I avoid heating of the IC by adjusting the period?
    Can I accept this 4ms period?
    No need of PWM. Charge for 1 second, give a gap of 5 mS and then continue.
    How to determine that battery is fully charged?
    When the voltage starts dropping. It is called negative delta V method.
    2cells.. means1.25x2=2.50v..I heard that fully charged 2cells maintain 3.96v across across it.Is that currect?
    I am using buit in a2d to check the voltage.I heard about dv/dt checkig of battery..Whats meant by that?How check dv/dt?
    dV = previous voltage - present voltage = negative or zero, keep charging.
    dV = previous voltage - present voltage = positive, terminate charge.

    Google for negative delta V and you will come up with many results.

    Cheers

    Ravi


    Hi Ravi,
    Thanks for sugessions.I want to use pwm because I am planning to charge the batteries at different modes.ie, slow charging,medium,fast,or any thing between these.If i am not hurry to get the battery to be fully charged then i can switch it to 4% of C charging mode...etc.For this pwm is easy ,because i only need to change the timer value for various modes..

    I read the article on http://www.angelfire.com/electronic/hayles/charge1.html
    I got the idea of dv/dt method...thanks for giving the logic..

    The IC LM317 is configured in constant charding mode in that article.I am using that circuit,and switching the IC as I needed.What is the specification for transformer i need to use.Currently i am using 7-0-7/1A.But when I am swiching the charger in to fast charger mode the pic resets,because of the voltage drop in the supply.I dont want to use a bulky transformer.Any trick to use the same transformer?

    Thanks...

    Regards..........



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    pwm nimh charger

    Quote Originally Posted by sajeev
    Thanks for sugessions.I want to use pwm because I am planning to charge the batteries at different modes.ie, slow charging,medium,fast,or any thing between these.If i am not hurry to get the battery to be fully charged then i can switch it to 4% of C charging mode...etc.For this pwm is easy ,because i only need to change the timer value for various modes..
    Changing the PWM values will not allow you to change modes since the charging current will be the same. You will have to change the charging current for different modes.
    The IC LM317 is configured in constant charding mode in that article.I am using that circuit,and switching the IC as I needed.What is the specification for transformer i need to use.Currently i am using 7-0-7/1A.But when I am swiching the charger in to fast charger mode the pic resets,because of the voltage drop in the supply.I dont want to use a bulky transformer.Any trick to use the same transformer?
    As you are in Bangalore, PM me and I will give you my telephone no. Call me and I will help you out.

    Cheers

    Ravi



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    pic charger

    Hi
    I read the code for intelligent battery charger using pwm.I changed the assembly code in to C(Hitech C.) with some modification.The charger is working fine.I used pic16f73 instead of pic16f711.For a2d i used the ref voltage as 2 and max charging current as 560ma(1.25/2.2=560ma).Now the problem is after charging the battery with full current its switchung over to trickle mode with in 10 or 20 minutes.I used 2500mah NIMH battery (2 in series).I dono whether the battery is good or not.I tried with adjusting the count3 variable to higher values like ..4,5..What may be the reason?How can i check whether battery is good or not?
    I will upload the code and hardware..


    Regards
    sajeev
    sajeev_ev at yahoo.co.in



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    lm317 charger+pic

    I read the code for intelligent battery charger using pwm.I changed the assembly code in to C(Hitech C.) with some modification.The charger is working fine.I used pic16f73 instead of pic16f711.For a2d i used the ref voltage as 2 and max charging current as 560ma(1.25/2.2=560ma).Now the problem is after charging the battery with full current its switchung over to trickle mode with in 10 or 20 minutes.I used 2500mah NIMH battery (2 in series).I dono whether the battery is good or not.I tried with adjusting the count3 variable to higher values like ..4,5..What may be the reason?How can i check whether battery is good or not?
    I will upload the code and hardware..
    For NiMH battery, you will have to use - delta V method to check if the battery is fully charged.

    Once the battery is fully charged, the voltage will start to drop. This is when you have to terminate charge or when the temperature raises too fast.

    Do not charge continuously. Charge for 1 second, leave a gap of 5 mS and then repeat the same procedure. In the 5 mS gap, check the voltage to see if the voltage has dropped compared to the earlier reading.

    Cheers

    Ravi



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    battery charger pwm

    wat program did u guys use?
    does anyone use pic basic pro?
    wat software u guys use to draw the circuit?



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    lm317 pic

    Hello everyone...I'm so happy reading this topic about battery charger using micro-controller....:D

    hi sajeev...i also work in a project almost the same with the topic you post...but i really really need helps for my project....because this is my final year project of my studies...
    My project tittle is "Smart Battery Charger with Micro-controller".....i need to charge 2500 mA-hr NiMH AA rechargeable battery which is connected in parallel and need to be charge in 1 hour or less...i used LM317 as voltage regulator.....
    .most of the battery charger i found do not charge battery in parallel but in series....

    so how about if i want to charge a battery in parallel...?? means i can increase the number of battery to be charge at any time but still i can control the charging current so that charging time is less than 1 hour....how to control (using PIC16F84A) the charging current to the battery if the number of battery are increased or decreased..??

    TQ....hope somebody can help..



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    pwm nimh

    A Charger For Deep-Cycle 12V Batteries, Pt.1

    Published: 29 November, 2004 Silicon chip

    A Charger For Deep-Cycle 12V Batteries, Pt 2

    Published: 15 December, 2004 Silicon chip
    http://www.siliconchip.com.au/cms/A_103239/article.html



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