VRLA AGM - Battery Charger

Discussion in 'General Electronics Chat' started by Mad Professor, May 30, 2009.

  1. Mad Professor

    Thread Starter Active Member

    Apr 15, 2009
    133
    1
    Good Day All.

    I have got a pair of VRLA AGM batterys taken from a broken mobility scooter.

    A quick google search gave me a link to good old wikipedia.

    VRLA: Valve Regulated Lead-Acid.
    AGM: Absorbent Glass Mat.

    The batterys are made by Haze but the lable with the model number is missing.

    The only thing I can tell you is that they are both 12v batterys, and aprox 195x130x160mm (WxDxH).

    On the side of the battery it has a lable saying.

    Battery Charging
    Float Application: 2.27 to 2.30 vpc @ 20 Deg C.
    Cycle Application: 2.35 to 2.40 vpc @ 20 Deg C.

    As this is a Lead-Acid type battery can I use a standard car 12v Lead-Acid battery charger, or will I need a battery charger designed for this type of battery?

    Thanks for your time.

    Best Regards.
     
  2. Smoke_Maker

    Active Member

    Sep 24, 2007
    126
    15
    A 12 volt battery charger will work but don't let it go over 14.8 volts, keep a eye on it with a volt meter. You can find a inexpensive charger at auto parts or sears or kmart that has AGM setting on it.
     
  3. Externet

    AAC Fanatic!

    Nov 29, 2005
    758
    57
    2.40 vpc means volts/cell; which adds up to 14.4V maximum. 14.0V should be a safe margin to charge them, and a plain decent car battery charger should be able to regulate that.
    To leave the charger connected long times, 2.28vpc adds up to 13.7V

    It is good you have the charging recommendations from the manufacturer.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Note that the temperature is also specified for the vpc.

    Lead-acid batteries have a negative temperature coefficient that's roughly 3mV per cell per degree centigrade; since you have six cells per battery, that's 18mV per degree centigrade.

    Note that charging at high current levels will increase the internal battery temperature. It takes a very long time for a battery to cool off once heated.
     
  5. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    We have just been through the repair of the charger for one of these in this thread

    http://forum.allaboutcircuits.com/showthread.php?t=13256

    The charger spec is posted in the first picture. The scooter (and charger) is 24 volts and the 2 scooter batteries are charged in series.
     
    Last edited: May 31, 2009
  6. Mad Professor

    Thread Starter Active Member

    Apr 15, 2009
    133
    1
    I have a RAC HP026 Lead-Acid battery charger for my car.

    I am able to select fast or trickle charge.

    Fast Charge = upto 8amps @ 12volts output.
    Trickle Charge = upto 2amps @ 12volts output.

    I have not tested the charging voltage with my DVM.

    Would it be best to just use the Trickle Charge.

    Best Regards.
     
    Last edited: May 31, 2009
  7. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    So long as you control the charging manually either would work.

    However I would not run at the 8 amp level for more than 30 minutes at a time as you can boil the fluid and bend the plates through overheating.

    So the 2 amp rate is safe unattended overnight, the 8 amp rate is for boost. I expect it says something similar in your charger manual.

    You should realise that you can only charge one of your batteries at a time with your charger? If you try to charge the pair in parallel the current probably won't distribute evenly.

    Here is a thread with a discussion about more sophisticated chargers.

    http://forum.allaboutcircuits.com/showthread.php?t=16711&highlight=charging+lead+acid+batteries
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Using the trickle charge would minimize the internal heat buildup.

    Getting a battery hot reduces it's lifespan due to greatly increased chemical activity.

    You can measure your battery's internal temperature by the positive terminal. If you decide to try the fast charge, I suggest monitoring the battery internal temperature, and reduce the charging rate once the temperature has increased.

    Here's a chart for you; charge and float voltages over temperature for your particular batteries.
    [​IMG]
     
  9. Mad Professor

    Thread Starter Active Member

    Apr 15, 2009
    133
    1
    Thanks for your replys.

    I am only going to charge each battery in turn as I have no need for 24volts.

    Thanks again.
     
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