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How to Charge Batteries in Parallel or Series?

Discussion in 'Home Power and Microgeneration' started by Neil P, Sep 10, 2003.

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  1. Neil P

    Neil P Guest

    For the 6v golf cart type, do you charge each one individually?

    And for parallel configuration, lets say we have 2 deep cycle 115 Ah
    batteries in parallel, would a 2/20 automatic deep cycle charger capable
    of charging both at the same time?

    Thanks for your inputs,
  2. BugHunter

    BugHunter Guest

    You can charge any number of batteries at the same some, with the correct
    voltage charger.

    For example Two 6v golf cart batteries hooked up in series can be charged
    with a 12v charger. Four 6v batteries wired in series-parallel to make a 12v
    bank could also be charged with the same 12v nominal charger.

    The larger the rating of the charger in amps, the faster the batteries will
    charge. Well, within limits. An undersized charger will take lots of time.
    Two large a charger (if not throttled back) could cook the battery. you want
    to have a reasonable match between the charging amps that you produce and
    the capacity of the battery bank to accept that charge.

    For off grid applications with large battery banks, you typically would try
    and get the biggest charger you can to minimize run time of generators which
    are noisy.

    I have used a 10 amp charger to charge 4 220 amp-hour 6v batteries. It takes
    forever. A 35 amp charger does it a whole lot faster. I would not be afraid
    to try a 170 amp charger.

    Think of your battery bank as a water tank (both have storage capacity). A
    more powerful pump can fill you tank faster. But, the hose connections
    (voltage) still need to match between the tank and pump.

    A 2/20 (amp) charger would be adequate for 230amp hour battery bank as long
    as it was voltage matched to the bank configuration.
  3. Charging batteries in parallel CAN cause problems if the batteries are
    not matched. That's why it is better to use 2 honking big 6 volt golf
    cart batrteries in series than 2 12 volt batteries of the same
    physical size in parallel.
    A battery is multiple cells in series, so putting multiple batteries
    in series still gives you a battery. Multiple batteries in parallel is
    still multiple batteries.
  4. Neil P

    Neil P Guest

    i am deciding: 2 6v golf cart in series or 2 deep cycle (identical) in parallel

    i will be charging from grid power, so i am thinking that a 2/20 would be
    sufficient for either 2 6 volts or 2 12 volts with 115 ah each. sounds good?

    thanks again,
  5. As Clare said, 2 golf cart batteries in series will give you better
    results, and more even charging (charge current will always be exactly
    the samein both batteries).
    Be aware that an undersized multi-stage charger may never reach the
    'current dropped below some threshold, so I should switch to a lower
    voltage' state. I saw this happen recently with a 6V golf cart
    battery and an Accumate charger from and it
    ended up boiling the battery without switching to the 'float' mode.

    A Trojan T-105 is the 'standard' for golfcart batteries, and it's a
    couple hundred amp-hours. A 20-amp taper charger isn't bad if you
    don't mind 24 hours or more for a charge, and 2 amps is probably a bit
    much for a float charge. Why not get a real multi-stage charger from
    (say) Trace/Xantrex, or if you haven't already bought the inverter, an
    inverter/charger from them...
  6. Neil P

    Neil P Guest

    dont mind 15-24 hrs to recharge, just want to have a good setup where i recharge at
    the right amps and float as well without any "cooking"

    i have the inverter already, i am trying to locate a suitable charger locally. what
    amps should a float charge be at?

  7. Well, it probably shouldn't be "amps" that you float charge at, but
    volts. While constant current float charging has some advantages,
    most 2 or 3 stage chargers end up float charging at a fixed voltage.

    If you have an automotive battery charger with a "2-amp" and a
    "20-amp" switch, that's not at all suitable for unattended battery
    charging, and not very good for attended battery charging, because it
    requires close attention to battery current and voltage, and if you
    get distracted and walk away, you'll boil your batteries dry in short

    Look on the Xantrex WWWebsite for 2 and three stage chargers.
    Basically they are a current-limited high-voltage charger that waits
    for the current to get below a certain threshold, when it switches to
    a lower voltage for float charging.

    A battery temperature probe is best, as it'll tweak the float voltage
    setpoint to exactly match your battery. The size of the charger ought
    to be compatable with the capacity of the battery (within some range)
    to avoid the "wait till the current drops below some threshold" mode
    from getting stuck or easily confused.
  8. Neil P

    Neil P Guest

    Thanks for the ideas, however at this time I am using 1000 watt inverted bought at
    Costco (modified sine) for 69.99. I am looking for a low cost backup to grid power for
    max of 2-3 hrs and max of 200 watts. I am on my way with the battery and saw automatic
    chargers that list 2/20 and was wondering if the 2 am is too much to trickle charge.
    Schummer (sp) sells the charger and they have a 1.5 amp trickle charger that turns on/off
    to maintain the battery. Am wondering if this is safe for my operation?

  9. I'm not sure what they mean by 2/20, can you clarify that 'spec' for
    That one looks OK, though only for float charging of course, and I
    can't say much about the manufacturer. On the other tentacle, the
    Xantex TrueCharge 20+ seems to go for around $250, which will buy you
    a lot of batteries... 8*)
  10. Neil P

    Neil P Guest

    2/20 on this charger that is automatic says: it will start out at 20 amps and trickle down to
    2 amps to float and turn on/off to maintain the battery.

    I have recalculated my use for power outage, and all I need is 11amps/hr. I have my eye on a
    12V 115 amp/hr deep cycle battery. 50% of that conservatively is say: 50 a/hr. At 11 amp/hr
    need, I can run for approx.: 4 hrs and only discharge the battery to 50% or more.

    Based on this would a 10 amp charger be fine and the 1.5 amp float charger to maintain the
    battery year round?

  11. Well, if it really does turn off and is an automatic battery charger,
    then it should work just fine.
    You are having a little confusion with your units, amp-hours is a
    quantity, and amps is a rate of flow, but if I understand that you
    only need 11 amps for 4 hours then that should be fine.
    Well, you have to decide what you want your recharge time to be (if
    this is for the occasional blackout then a week to recharge won't
    bother you). Is the 10 amp charger automatic? [I really wouldn't
    reccomend a non-automatic charger, as you _will_ forget and leave it
    on too long.]

    The 1.5-amp float charger looks OK, but if they 2/20 charger
    referenced above is properly sized for your battery and really does
    turn off when the battery is charged, then it should be OK. Check the
    voltage and electrolyte level regularly until you know what your
    maintenance interval should be.
  12. Bob Adkins

    Bob Adkins Guest

    This would not apply to low a current charge, such as a small PV array,
    correct? Seems that the batteries would have plenty of time to "level"

  13. Bob Adkins

    Bob Adkins Guest

    This sounds perfect for a 115 AH battery.

    If you don't discharge it to 50% more than 2-3 times a year, it should last
    a long time.

  14. Neil P

    Neil P Guest

    i will have a calibrated digital voltmeter (calibrated at work, EE company) that will monitor my
    battery. My battery selection is now a 12v 115 amp/hr deep cycle battery. My needs are tops 11

    Somewhere i read there a c/10 rating for the battery, in my case a 10 amp charger should be fine
    with a 2 amp floater? There is a 2/10 automatic deep cycle charger i see available locally.

    Thanks again, much appreciated.

  15. More critical in some ways. If you have one bad battery (shorted cell,
    or partially shorted cell) it will drain the good battery as fast or
    faster than the PV can recharge - so your batteries are always low.

    With series connection and a shorted cell, the other cells will be
    slightly overcharged, and overall pack voltage will be low.
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