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Sealed Lead Acid Batteries

Discussion in 'Power Electronics' started by deepfriedcircuit, Feb 10, 2015.

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  1. deepfriedcircuit

    deepfriedcircuit

    5
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    Feb 10, 2015
    Hi Guys,

    First post here so go easy on me. (I'm still testing the waters).

    I've been interested in electronics for a while now, building circuits from kits mainly and doing small modifications here and there.

    Heres my story:

    My Dad asked me to look at his Home Security System and I was dumb founded by his simple question.

    The unit, a HoneyWell Vista 20p, is reporting that the 12v 5AMP Sealed Lead Acid Battery is low.
    We discovered that the main unit was accidentally unplugged from the main power supply so we determined that it must have been running off the back up battery for a while now.

    I found some chargers online and Black & Decker BM3B 6V and 12V Battery Charger / Maintainer looks nice.

    Few Questions:
    If we plug the main unit back in will the backup battery charge on its own?
    Since the battery is 12v could we use an automobile battery charger?
    What is the best way to test the Charge using a multimeter?

    Also any other recommended reading or resources (products, websites, ect.) would be greatly appreciated about power supplies and sealed lead acid batteries in general.


    Thanks a lot!
     
  2. Bluejets

    Bluejets

    5,034
    1,051
    Oct 5, 2014
    Fit new battery, if existing was left without charge for "a while" then chances are it will be dead (replace with same type) Test voltage (should be around 12 volt or slightly higher) plug in main unit to mains supply
    Recheck battery voltage starting to increase in value over a period of approx 5 minutes.
     
  3. Externet

    Externet

    775
    168
    Aug 24, 2009
    If we plug the main unit back in will the backup battery charge on its own?
    ---->It should. There has to be a trickle charger/maintainer circuit built-in. Allow several hours. A lead-acid that stays discharged over 24 hours will never recover its full capability, but may still work somewhat.

    Since the battery is 12v could we use an automobile battery charger?
    ---->Yes

    What is the best way to test the Charge using a multimeter?[/QUOTE]
    ---->Check for 12.6V to 13 V while connected to charger after a while; or whatever directions are stamped on the side of the battery for charging/floating.
     
  4. Gryd3

    Gryd3

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    875
    Jun 25, 2014
    You can test the battery connected to the alarm as well.
    Testing a battery by itself will most likely tell you a higher voltage than it actually is.
    Leaving it connected to a load is the most reliable way to test the voltage.
     
  5. deepfriedcircuit

    deepfriedcircuit

    5
    0
    Feb 10, 2015
    Hey thanks for the quick responses guys. The battery is not completly dead yet so im going to try testing it, plugging it back in to the wall for a week and then testing it.

    Interesting that leaving it connected to the load is the the best way to test it. Why is that?
     
  6. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    When you are not drawing any current from a battery, it's considered an 'open circuit' and will show the total available voltage...
    When you begin to draw current from it, the internal resistance in the battery will cause the voltage to drop. Batteries in poor condition have high internal resistances, which may look good 'open circuit' but will drop too far if they attempt to provide any current.
     
  7. Arouse1973

    Arouse1973 Adam

    5,164
    1,087
    Dec 18, 2013
    Hi

    Do not use a car battery charger to charge sealed Lead acid batteries. They can be damaged and potentially could explode. Either buy a correct charger for sealed batteries or use the equipment that the battery came from to do the charging.

    Thanks
    Adam
     
  8. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    This rule can be bent if you can adjust the output current...
    automotive chargers will attempt to shove too much current in. Good call Arouse.

    So, to revisit Externet's answer on automotive chargers. No, but it is possible with the correct equipment and knowledge.
     
  9. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    Some battery charging circuits require a minimum voltage across the cells to work. (if for example the battery open circuit voltage drops below 9 Volts the charger will not output any cuurent to the battery on some chargers. It is best to use the correct OEM charger and battery combination. You can test to see if the charger is working by inserting a DC ammerter in series with the charging cable.
     
  10. Arouse1973

    Arouse1973 Adam

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    1,087
    Dec 18, 2013
    Absolutely, there are no rules that should be bent, batteries are dangerous, the small sealed batteries can explode if treated incorrectly. Car chargers are for car batteries, sealed battery chargers are for sealed batteries and gel battery chargers are for gel batteries. Some chargers say they will charge different types by selecting a different charging profile, that's fine.

    The issue you have to watch out for with especially gel batteries is that the battery does not enter its gassing stage, I can't remember what exact voltage that is per cell. Some batteries need the gassing stage to mix the electrolyte solution. Gel batteries and AGM batteries don't. This is why you have to be careful.

    Adam
     
    Last edited: Feb 11, 2015
  11. Arouse1973

    Arouse1973 Adam

    5,164
    1,087
    Dec 18, 2013
    It is best to connect the battery to the equipment and not any load. After all the equipment is what the battery is supposed to be running.
    Adam
     
  12. BGB

    BGB

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    Nov 30, 2014
    in my case, I am charging lead-acid (UPS style, AGM/VRLA) batteries using a variable power supply (for powering some current battery-powered projects).

    I have noted that even in the "Small/AGM" mode on an automatic charger, it gives behavior that doesn't seem quite right (such as trying to charge at 15.5 or 16v when the battery is only rated for charging in the 14.4-14.9 range), and/or very quickly dropping down to maintenance charge mode (13.6v) even if one had been using a bit of a load on the battery.

    so, yeah, I think by "small", they are still thinking of "slightly larger" batteries (just small relative to a car battery).

    so, yeah, I had been doing some things manually, cycle-charging them after use mostly at 14.4 to 14.6v until the charge current mostly drops off (also noting that after use, they don't really seem to charge below about 14.4v, as-in, if you discharge them some and put them back on 13.6v, they don't really pull in any current), ...

    me hoping I have been doing all this "about right".
     
  13. Arouse1973

    Arouse1973 Adam

    5,164
    1,087
    Dec 18, 2013
    There is nothing wrong with this as long as you ensure the charging current at the start is approx. 1/4 of the battery capacity until the absorption stage voltage is reached say 14.7 Volts. Then monitor the current until it's about 0.7% of the capacity and then switch over to float charge of 13.8 Volts.

    Sealed batteries are sensitive to this absorption voltage and this must be monitored. A standard car battery charger normally doesn't do this so it's better to do as you have been doing or buy a charger that does it for you.

    One other thing a battery must be charged with no load if you are using an auto charger otherwise this can confuse them and they may not come out of absorption charge. We had this problem with some of our equipment and the large batteries were dying in 6 months.

    That's my opinion anyway

    Thanks
    Adam
     
  14. BGB

    BGB

    154
    11
    Nov 30, 2014
    yeah, lead-acid batteries are sort of annoying in some ways.

    hadn't been that precise, just noting that after a little while current draw gets pretty low.

    0.7% C seems about 0.06A.
    the batteries like to hang out for a while at around 1% though.


    though, there are a lot of tradeoffs between them and some other options, like NiMH or LiFePO4 or similar (ex: they are cheaper and have lots of amperage, but not nearly as much usable capacity).

    nearly all of them have some annoying quirks as well WRT charging.

    or such...
     
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