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    Battery charging question

    Dear forum members,

    i Have a question about charging batterys. (I'm a engineer and don't know too much about elektronics) I have a 12v battery at home (Picture 1), it is low on charge and i dont have a fitting adapter to charge it nearby. I did however find a adapter that seems fitting (picture 2). I tried to google info about charging lead acid batterys, but there is so much information and different opinions about it i don't know which is right.

    I learned (might be wrong):

    - Voltage is being pushed by the adapter, which is 12v so still within limit range of the battery, should be ok?
    - Amps are drawn by the battery, so should be ok aswell even if the adapter amps are higher?

    Can i charge the battery using this adapter by cutting the adapter wires and connecting them with the right polarity on the battery clips?

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  2. #2
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    Re: Battery charging question

    Hi,

    A google search sometimes is not useful ... at least donīt rely on random hobbyists statements - they might be true, they might be wrong..
    --> find reliable informations at the battery manufactuer
    --> find reliable informations at the big battery charger manufacturer
    --> find reliable informations at dedicated sites, like http://batteryuniversity.com/

    The adapter you have is no battery charger, it is just a 12V power supply. --> It is not suitable to charge a 12V battery

    Charging a battery needs a valid charging mode. Charging mode depends on battery chemistry. In your case it is a "sealed lead acid battery".
    ... and if you read the battery informations you find the maximum charging voltages for different charging types.
    To charge a 12V battery you need (much) higher charging voltage than the rated battery voltage: In your case for CICU I recommend to use 13.8V maximum.

    Klaus
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    Re: Battery charging question

    Thank you for taking time to answer Klaus,

    Makes sense, I'll look online to get a proper charger for this battery. Good thing i asked because i was tempted to just try it out, would probably have screwed the battery and maybe even created a dangerous situation



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    Re: Battery charging question

    charging a 12 volts battery 14 volts are o.k. As a general thumb rule for the current you should have at least 10 % charging current capacity for the charger .for example your SLA battery is 7 amp/ h rating you need at least 700 ma charger or 1 amp is also ok. but you have to care full about initial charging of battery current when battery is more discharge it try to draw more current and it could be beyond your charger capacity.you can 1 amp fuse in series either cable negative or positive to save your charger.
    actually very battery type have its own charging profile and smart charger take care of it.



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    Re: Battery charging question

    Hi,

    I don't agree.
    Many recommendations say to use: max_charge_current = battery_charge / 10h.
    This us a rule not to stress the batteries.

    But in detail it mainly depends on battery chemistry and battery type.
    If you want to use higher charge then I recommend to read the battery datasheet, or contact the manufacturer.

    Klaus
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    Re: Battery charging question

    Quote Originally Posted by engineerpervez1 View Post
    charging a 12 volts battery 14 volts are o.k. As a general thumb rule for the current you should have at least 10 % charging current capacity for the charger .for example your SLA battery is 7 amp/ h rating you need at least 700 ma charger or 1 amp is also ok. but you have to care full about initial charging of battery current when battery is more discharge it try to draw more current and it could be beyond your charger capacity.you can 1 amp fuse in series either cable negative or positive to save your charger.
    actually very battery type have its own charging profile and smart charger take care of it.
    It is perfectly correct for all lead acid batteries and even SLA batt, because 1/10th of Ah is the least possible current you are using for charging the battery, and that will ensure minimum stress to the battery. This rate can be even used for LI-Ion or Lipo batts, if a delayed charging is acceptable.
    Just make sure to cut off the supply after 14V or keep it on a trickle charge



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    Re: Battery charging question

    I think the issue here is between "charging current" and "power supply maximum load". To avoid stressing the battery the current should be set to about 10% of the battery rated capacity, so for 7 Amps, 0.7A (700ma) is about right.

    However, that is for charging under normal circumstances, if the battery is discharged , applying even 12V directly across it will try to make considerably more current flow and that small power supply will probably be overloaded and hopefully will shut itself down.

    As advised, you need a higher voltage to 'pull the battery voltage up' to 12V, typically around 13.8 to 14V but you also have to limit the current to the C/10 value to protect the battery and PSU. That's why normal constant voltage chargers are not suitable for charging batteries.

    Brian.
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    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



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    Re: Battery charging question

    Here is a Poor Man Charging solution. Not that I think you may be a poor man, but hey, anyone can use a little inexpensive trick once in a while :)
    Your power adaptor is adequate for changing your battery providing that you impose a current limitation strategy to be on the safe side.
    Just connect your 12Vdc adaptor in series with an Incandescent car light bulb. This will drastically limit the output current, will slowly charge your battery and will certainly not permit the battery to become overcharged, since a 12V lead battery can be maintained at 13.8V during a very very long time.
    Just check your battery voltage in a day and it should be charged (not fully, but usable)



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    Re: Battery charging question

    Hi,

    You simply can't charge a 12V battery with a 12V supply. You need a higher voltage.
    Please read at batteryuniversity.com.
    You won't get more than 10% of rated energy into the battery ... not in a week.

    Klaus
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    Re: Battery charging question

    I learned how to calculate current for the battery, but i did not understand how did you calculate volts to charge a battery, for example if want to charge 5v 1A battery how will i calculate the volts to apply,

    Thanks.



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    Re: Battery charging question

    Hi,

    Read post#2.
    The max charging voltage depends on chemistry and charging mode.
    Again: look at batteryuniversity.com

    Klaus
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    Re: Battery charging question

    Hi,

    For lithium ion batteries, we usually connect the battery to a bench power supply by setting the proper voltage and current. For eg. for a li ion 3.7V battery, the full charge voltage is 4.1V. After setting the 4.1V and proper current on bench, connect the battery directly. So when the battery is fully charged the current become zero.. because of same voltage on both sides.



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    Re: Battery charging question

    Hi,

    You can do this with your own batteries on your own risk.

    But itīs not the recommended charging method for a LiIon battery.
    There are a lot of LiIon batteries beeing exploded and causing fire because of inappropriate charging methods.
    * you need a current limiter in either case
    * There are different LiIon types with different voltage levels
    * you need to keep these levels tightly tolerated (often a bench power supply isnt useful for this)
    * it is recommended to monitor battery temperature and stop charging on temperature rise.

    The problem with LiIon is that - when not treated correctly - they tend to self distroy themselves. This causes the stored energy to be released within a short time. This is some kind of avalanche effect. Causing heating, explosion, fire.

    Read batteryuniversity.com BU-409: Charging Lithium-ion how to charge LiIon correctly.

    Klaus
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  14. #14
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    Re: Battery charging question

    Hi,

    Yes, I agree with that. this is not the recommended charging method. But it is not that much dangerous. We have done it several times. If careless then it will be a problem.
    Only point to be noted that we tried only for 4.2V range batteries, not in 12V ones.
    What we do is,
    1. check with the voltage level of Li ion. from the datasheet or from manufacturer.
    2. Then we are limiting the current in bench power supply. The option is there in all bench I think.
    3. Monitor it till current becomes zero. stop charging it.
    Continuous monitoring is needed that's all I think.



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