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battery charger

Discussion in 'General Electronics Chat' started by taimoorkb, Oct 7, 2007.

  1. taimoorkb

    Thread Starter New Member

    Oct 2, 2007
    using a bridge rectifire i have converted 220v ac to dc from the equation Vo=2/t* with the integral of Vm Sin@d@ with limits zero to pi and solving it i got 198v dc now i want to charge 10 12v batteries which are connected in series assuming that i will get a voltage drop of 12v across each battery, how can i step down 198v dc to 120 v dc, also do i need a charging circuitry. the battery which will be used is a 12 v lead acid battery of 80ah......... is there an easy solution for it .......thank you...
    taimoor khalid
  2. SgtWookie


    Jul 17, 2007
    Working directly with 220/230 VAC line voltage is VERY hazardous. I strongly recommend against this approach.

    Instead, use a step-down transformer, in the neighborhood of 14 to 18 VAC or 28 to 36 VAC center-tapped.

    Use a bridge rectifier after the transformer to get your DC output. Use some good-sized electrolytic caps of appropriate voltage rating to smooth out the ripples.

    Take a look at a datasheet for LM138/LM338 5-amp voltage regulators available from National Semiconductor. Download the datasheet from their site. On page 11, there is a schematic for a 12V battery charger.

    When lead-acid batteries are brand new, batteries of the same exact make/model will charge/discharge at nearly identical rates. This can change as they age, particularly if they get "deep cycled". This can cause significant corrosion/sulfation to form on the plates, changing their capacity very significantly.

    If you can get ahold of a really heavy-duty 220v transformer, you could build a number of charger circuits to "feed" from this main supply. Otherwise, you could build a circuit to "round robin" charge them; when one cell was charged, switch to the next one in sequence and charge it.
  3. techroomt

    Senior Member

    May 19, 2004
    batteries can be charged with full wave rectification. charging ten 12vdc batteries in series will require a voltage of about 14.5 vdc per batt, or 145vdc. bridge rectification of 220 vac (rms) will render appx 313 v peak full wave dc, which when converted to average is appx 201 vdc. so you're ~ 55 volts high. you will need to steop that own with a line transformer, or voltage regulator. as far as the charging circuitry, it depends on the automatic features vs hands on monitoring you wish to design in.

    however i think that last time i saw this work the batteries on the end seem to draw more, and overcharge quicker then those in the middle - i can't explain this though. maybe someone else has experience here.
  4. thingmaker3

    Retired Moderator

    May 16, 2005
    Wrong equation. Sorry.

    Read Sgt.Wookie's reply carefully. He gives good advice.

    I've seen inconsistent charging when undersized leads were used. If the leads are not big enough, the voltage drop across them becomes a problem.