Help required for this SMPS Battery Charger

Discussion in 'General Electronics Chat' started by xyz9915, Jun 7, 2008.

  1. xyz9915

    Thread Starter Member

    Feb 24, 2008
    23
    0
    Hi! The attached file is a schematic of 50KHz SMPS power supply which uses 325 VDC (after rectification of Mains 240 V). The required current for charging Lead Acid battery is approx 20 Amperes. Please give comment if any modification in the circuit is required. (note: isolated 12V DC is used for control circuit)
    Voltage regulation is not necessary.
     
  2. S_lannan

    Active Member

    Jun 20, 2007
    247
    2
    do you know how to properly charge the type of battery you are charging?

    That circuit could blow up the battery if the current isn't controlled
     
  3. xyz9915

    Thread Starter Member

    Feb 24, 2008
    23
    0
    The battery type is lead acid with 190AH capacity so the charging current up to 25A is not harmful for battery
     
  4. S_lannan

    Active Member

    Jun 20, 2007
    247
    2
    But there is nothing to say the charging current will hold at 25amps.
    That circuit would be quite capable of supplying a lot more and probably will try to supply more until something blows.

    I have no real knowledge on battery chargers.

    but make sure you know enough about them before you test this
     
  5. xyz9915

    Thread Starter Member

    Feb 24, 2008
    23
    0
    Thanks for reply. I noted the point, so can you guide how do I modify the circuit to deliver about 15 Ampere to charge the battery or if you know a better design please provide it.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    T1 in the schematic isn't drawn correctly; it shows the primary as center tapped, but it shouldn't be a center tapped transformer.
    The number of turns on the transformer core are specified, along with a specific core, but no mention of wire gauge.

    The output side of the transformer is not regulated. This in itself isn't a huge problem for a battery charger as long as the maximum battery charging rate is not exceeded, and the current is cut off or reduced as the battery reaches a full charge. There are no provisions for this. One would need to either add such circuitry, use a timer to control the length of time the battery is charged and set it accurately depending upon the initial charge level, or monitor the charging as it progressed.
     
  7. xyz9915

    Thread Starter Member

    Feb 24, 2008
    23
    0
    The changes/modification proposed by the forum members, the modified circuit is attached herewith with feedback control circuitry to keep the design stable. Please point out if any further modification is required.
     
  8. S_lannan

    Active Member

    Jun 20, 2007
    247
    2
    apart from the primary and secondary no longer being isolated... (don't cook yourself now)

    seems like your starting to get it together.

    did you design the compensation circuit yourself or just put in some kind of rough estimate?

    an important feature would be to prevent overcharge.

    a microcontroller would be nice for this project. It would make the charger very flexible and easy to modify.
     
  9. xyz9915

    Thread Starter Member

    Feb 24, 2008
    23
    0
    AC mains isolation is not required. I have main focus in the power section to make it feasible. while the charging On/OFF control will be made with the help of operational amplifier. so please guide that the SMPS section is OK or required to be modified?
     
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I don't know what your reasoning is for reducing the number of turns on the transformer core.

    I simply stated that it was not appropriate for it to have a center-tapped primary.

    I have no clue why someone chose the xfrmr core that was in the previous schematic.

    This looks rather "thrown together" from some off-the-shelf components without a lot of thought. Not the kind of thing one wants to do when working from the mains.
     
  11. xyz9915

    Thread Starter Member

    Feb 24, 2008
    23
    0
    The turns ratio reduced as the circuit was changed from push pull to half bridge. so it had to be changed according to the formula.
    Now following modification in the circuit is made with Opto feedback control circuitry to keep the design stable. Opto is used for a simple current regulation. Please point out if any further modification is required.
     
  12. xyz9915

    Thread Starter Member

    Feb 24, 2008
    23
    0
    After receiving many criticism in the design, I have changed the design by using UC3842 Current-Mode PWM Controller chip. The data sheet is available with various manufacturer, while one page from http://onsemi.com is shown in the attachment. The schematic is then modified by me to fulfill my requirements. So, please point out if any further change is required.
     
  13. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    In order to do this, you must first share your modified schematic...;)
     
  14. xyz9915

    Thread Starter Member

    Feb 24, 2008
    23
    0
    Thanks for reply. Both original & modified schematics are in the same sheet. The upper is from datasheet & the bottom circuit is the modification.
     
  15. gopal909

    New Member

    May 28, 2008
    3
    0
    hi T/F detail plz
     
  16. sathyananda

    New Member

    Mar 9, 2009
    1
    0
    Flyback topology is recomended where O/P power is <100, your o/p is 320W............
     
  17. timrobbins

    Active Member

    Aug 29, 2009
    318
    16
    Why is it not necessary to isolate the secondary side circuit from the primary side circuit???

    Why is there no inclusion of AC incoming protection?

    Are you planning to build this circuit yourself?
     
  18. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Gee, this thread had been dead for a couple of years...
     
Loading...