help for automatic battery charger!!! plzzz

Discussion in 'The Projects Forum' started by khmtambi, Jul 11, 2010.

  1. khmtambi

    Thread Starter New Member

    Apr 7, 2010
    14
    0
    hi all,

    i am new to this forum. well the purpose of starting the thread is to see if someone might help me on my 12v automatic battery charger. i have constructed the circuit as it is in the circuit diagram given but the problem is that ti is meant to supply 5amps of current at 14v(charging voltage) from a 15v transformer. but it is not supplying the current rated.it is only supplying 0.7A but it should provide 4-5amps ( i connected ammeter in series with the positive terminal of the charger). i want to know what the problem might be?

    also the circuit designer says that the curoff situation will build around 12.7v as the zener diode conducts and the transistor tp122 prohibits the working of charging transistor. but in my opinion zener diode should be of 13v and the cutoff situation should build around 13.7v (max 13.8 volts for max battery charge). i have posted the questions to the author but so far no responce which is very disappointing.

    and another last thing i want to ask is that i am actually trying to build a UPS and use this charger for charging my 200Ah battery. can this circuit be able to provide charging over a continuous period of time?


    hope i might get help from experts here. thanks in advance

    the original link for the charger is here
     
  2. tom66

    Senior Member

    May 9, 2009
    2,613
    213
    Some things to check:

    Check the main capacitor C1 for ripple.

    LM338 is rated for 5 amp max. Check the regulator is not going into shutdown from overcurrent.

    You have a 15 volt transformer. Remember this is usually volts rms. Volts peak is infact 15 * sqrt(2) = ~21 volts. Because of this, you will be dissipating well over 60 watts. Is this too much for your transformer? Or your regulator?
     
    khmtambi likes this.
  3. Dx3

    Member

    Jun 19, 2010
    87
    7
    The problem might be that the battery is fully charged.
     
    khmtambi likes this.
  4. khmtambi

    Thread Starter New Member

    Apr 7, 2010
    14
    0
    well the circuit is constructed according to the schematic. and all conditons are same. i have checked the voltage at every point including the IC. in case the ic lm338 is damaged can i use LM396 10amp adjustable voltage regulator ic? and yeah the transformer is big and i think it is capable of providing the 60watts or some less.
     
  5. Solcar

    Member

    Jun 8, 2007
    21
    3
    Hi khmtambi. The 10 amp regulator could be risky because it might permit overload of your transformer or rectifier diodes.
     
    khmtambi likes this.
  6. tom66

    Senior Member

    May 9, 2009
    2,613
    213
    If you have an oscilloscope, probe capacitor C1 and then show us the waveform. If it's got too much ripple the regulator might not be able to regulate. I have a feeling that C1's value (1000u) is way too low for 50 or 60Hz with a 5 amp load.

    How hot is the heatsink? Is it cool, warm or very very hot?

    Are you building it on a breadboard, stripboard, PCB or otherwise?

    Does the LED illuminate?

    When the battery is not connected how much voltage is present on the output?
     
    khmtambi likes this.
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The design will dissipate a tremendous amount of power in the regulator as heat. You will not be able to remove the heat fast enough, even if you had the regulator immersed in a huge body of ice-cold water. It will be very inefficient until the regulator overheats and shuts down, which will not be very long.

    1,000uF is no where near large enough.


    Beenthere posted a battery charger in the Projects section.
    Link: http://forum.allaboutcircuits.com/showthread.php?t=6099

    It uses a sensitive SCR to turn the charge current on and off.

    The battery is charged at the maximum capacity of the transformer, up to the set voltage.

    You need to find a datasheet for your battery, and follow the charging directions contained in the datasheet. If your battery internal temperature is higher or lower than 25°C, you need to adjust the terminal charge voltage by -18mV/1°C.

    If the battery is a SLA, it should be subjected to a brief high charge period daily.
     
    khmtambi likes this.
  8. khmtambi

    Thread Starter New Member

    Apr 7, 2010
    14
    0
    well i dont have an oscilloscope yet. and the heatsink is not at all hot. i have used a heatsink which is used in computer PSU. it gets warm after some hours. but i have used a fan to cool it. i am using veroboard ( or strip board if it is copper plated at the back and holes are there). LED illuminates and when the battery is not connected it says 13.3x volts( i have changed the transformer from 15v to 12v).
     
  9. khmtambi

    Thread Starter New Member

    Apr 7, 2010
    14
    0
    wow :D i didnt think how much complicated i can be. well should i use a 2amp transformer instead of using 5amp transformer? or should i just leave the circuit and use this circuit instead? i built it too but when it reached the cutoff situation the resistor r4,r5,r7,r8 went too hot and i had to turnoff the power but i am not sure that the circuit i built was exactly as given in the schematic.though i did check it several times but didnt find any thing wrong. still i think the problem was in the connections i made.
     
  10. tom66

    Senior Member

    May 9, 2009
    2,613
    213
    I'm not sure, but stripboard perhaps isn't the best idea. According to Google it's rated for 500mA per track, max. There's no way you can put 5 amps through it, so it could be that the track resistance is too high. In this case there's really little you can do.

    One thing you can try is replacing the 1000u with a 10000u (x10 bigger) capacitor, rated at 25 volts. Unfortunately this capacitor is quite a lot bigger in dimensions than your current one, they're also a bit rarer. Still I can't guarantee this will work.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Your first step is to find the manufacturer's datasheet for your battery, and post a link to it.

    Building circuits willy-nilly will only increase your level of frustration, and you will wind up with a battery that you have killed long before its' expected service life was up.

    You need to approach it in a logical manner. Start off by determining the battery maintenance requirements, and what your requirements are.
     
  12. rvh002@gmail.com

    Active Member

    May 15, 2009
    118
    2
    Work on 2000uF per amp of power drawn minimum. Capacitors must be rated at least 20% higher in voltage than your max. voltage.
     
    khmtambi likes this.
Loading...