12v adapter for charging 12v 7ah smf battery

Discussion in 'General Electronics Chat' started by getzme4u, Aug 12, 2011.

  1. getzme4u

    Thread Starter New Member

    Aug 12, 2011
    6
    0
    hello everyone
    i am getting stuck with 12 v 1 amp adapter and with 12 7ah smf leada acid battery .
    i give supply from adapter to battery through 1n4007 and then from this batttery to my microcontroller kit.
    by this my batteyr get charged and kit gets supply also at the same time but i am feeling there is some mistakes.
    so please guide me
    my need is: i am to chargemy 12v battery with 12 v adpter and continuoly give supply to my microcontroller kit.
    in that period it will cahrge battery and when power goes then give supply from battery
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If the supply is a regulated 12v supply, then your battery will never get fully charged, and it will soon fail.

    SLA batteries need to be charged to ~13.7v @ 25°C/77°F.
     
  3. getzme4u

    Thread Starter New Member

    Aug 12, 2011
    6
    0

    sir if battery wil not be charged full and my micorcontroller kit is also getting supply then how this battery wud be fail.
    there are three deives :
    1. 12 v 1 amp adapter
    2. 12 v 7 ah smf lead acid battery
    3. avr based microncrontroller kit
    these all positive and negative( ground )terminal are common with each other.
    and adapter have 1n 4007 diode in dirextion of battery so how wud the battery be failed please tell me.
     
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    Your battery will fail unless the correct charging current can flow until an appropriate end-of-charge voltage is reached.

    Your power supply may fail (burn out) unless the output current is prevented from rising too high if a discharged battery is connected

    If you want to leave the battery connected at all times, the charge current must drop down to a low value when an accurately defined "float" voltage is reached.

    These conditions are unlikely to be met if an unspecified "12V" power unit is connected to a battery via a diode, especially given that the supply is connected to another load.
     
  5. Brafferton

    New Member

    Feb 9, 2011
    6
    0
    Different metal combinations have different voltage characteristics
    For example:
    Carbon / Zinc is 1.5 volts per cell
    Nickel / Cadmium is 1.2 volts per cell
    Lead / Acid is 1.7 volts per cell

    http://forum.allaboutcircuits.com/showthread.php?t=55882
    shows an SLA charger circuit

    http://www.budgetbatteries.co.uk/battery-chargers/chargers/

    http://www.google.co.uk/products/catalog?q=lead+acid+chargers+12v&hl=en&cr=countryUK|countryGB&prmd=ivns&bav=on.2,or.r_gc.r_pw.&biw=988&bih=716&um=1&ie=UTF-8&tbm=shop&cid=8951228852605152681&sa=X&ei=aCNFTty0LMat8QO1l5jGBg&ved=0CGEQ8wIwAQ
    shows an off the shelf charger. I'm sure there are companies in your country that will sell similar items.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    That is not correct.
    1.7*6 = 10.2v, which would be a very dead 12v battery.

    It's closer to 2.133v per cell @ 25°C when fully charged, which gives you ~12.8v for a 6-cell battery.

    They should be float-charged at between 2.25v and 2.3v per cell @ 25°C, which is 13.5v to 13.8v for a 6-cell 12v battery.
     
Loading...