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What does the specification 12V 12AH /" /2HR" actually mean?

Discussion in 'General Electronics Chat' started by netfreak, Mar 7, 2012.

  1. netfreak

    netfreak New Member

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    Hello everyone,
    In my times I just used to hear specifications of battery like 12V 12AH which would mean that it had a voltage of 12V & 12AH means it can given currents of following values:
    1A for 12H
    2A for 6H
    3A for 4H
    4A for 3H
    & accordingly uptil 12A for 1H

    Now what I don't get is the "/2HR" thing that has on my battery. Please help me understand it that what does "/2HR" mean & what if it was "/10HR"? how much current for how much time would it deliver in that case?
     
  2. JMW

    JMW Member

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    Back in the olden days batteries were rated at an 8 hr discharge rate. That meant a battery could supply X amps for 8 hours.
    As batteries changed and the demands on batteries changed different discharge rates were applied.
    In general the higher the current draw the fewer "amps" can be drawn from a battery.
    So 1A for 12H means the battery will provide 1 amp for 12 hrs. There are some caveats, first this is dependent on temperature, it is specific, used to be 80 F. Second, the battery will not provide 12 amps for 1 hr, but it may provide .5 amps for 30 hrs.
    As for the meaning of "/2HR" or "/10HR" is there any other nomenclature?
     
  3. JimB

    JimB Super Moderator Most Helpful Member

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    Yes in theory.
    However in practice you will find that the faster you discharge a battery, the lower the capacity.

    So, lets say that a battery has a capacity of 12AH when discharged at 1amp,
    it may only have a capacity of 8AH when discharged at a 4 amp rate.
    The actual figures will depend on the individual battery type.

    Not quite sure, I have not seen that notation before.
    However I suspect that it means a 2 hour rate.
    So that the battery will supply its 12AH when discharged (at 6amps) over a two hour period.
    Similarly, if it said /10HR, the battery would supply 12AH when discharged at a current of 1.2 amps.

    If anyone else knows otherwise, please correct me.

    JimB
     
  4. dave

    Dave New Member

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  5. netfreak

    netfreak New Member

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    Sorry sir but I didn't get this thing "suppling 12AH" when discharged at 6 amps?

    Lets suppose I have a load which consumes about 1A, so by using the 12V 12AH/2HR battery for how much time would it work?
     
  6. netfreak

    netfreak New Member

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  7. JimB

    JimB Super Moderator Most Helpful Member

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    I suggest that you go and search the internet for a datasheet for this battery.

    I have just had a look and found some conflicting information.

    On one site I found, the /2HR does infer a 2 hour rate, ie the battery will provide 6 amps for 2 hours. (I do not believe that.)

    On another site I found some data tables for a similar battery which infer that the battery will only provide 12AH when discharged at 1.2 amps over 10 hours. This I will believe for that battery.

    JimB
     
  8. netfreak

    netfreak New Member

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    Um sir can you please make me understand on this thing " the battery will only provide 12AH when discharged at 1.2amps over 10 hours?" Do you mean to say that the only way for the battery to start its operation of delivering 12A would be to first discharge the battery completely by drawing 1.2Amps for 10 hours? Is this what you mean?
     
  9. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Think of x Ah as amount of gas in the tank. Think of y A-hrs as miles per gallon. Think of Amps as speed. The mpg(Amp hours) may be better under certain conditions.

    The relationships aren't exactly linear, but it does allow some comparison between the same chemistry. Actual performance must come from the datasheet.
     
  10. tvtech

    tvtech Well-Known Member Most Helpful Member

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    Ag.. I don't know anymore.

    What you posted there in the pics is a typical cheap sealed Lead Acid battery found on Chinese products..

    Not a quality product. Nothing to spec, because they have no specs....

    Good luck :rolleyes:

    Proper batteries from PROPER Manufacturers with some kind of reputation would serve you better than to try and learn from rubbish manufacturers...who have zero specs at all.

    I really don't know what else to say....except up your game. Try and learn from everyone except useless Chinese junk houses.


    TV Tech
     
    Last edited: Mar 7, 2012
  11. netfreak

    netfreak New Member

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    Um tell me this one thing guys :/ that if i constantly draw lets say 2A from it then for how much time this battery would operate?
    and also if i constantly draw 1A from it how much time would this battery work for ? by considering the "/2HR" thing
     
  12. tvtech

    tvtech Well-Known Member Most Helpful Member

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    am being kind here......please read my Battery post above. Please read...and try and learn

    TV Tech
     
  13. ronv

    ronv Well-Known Member Most Helpful Member

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    .6 amps - 20 hours
    1.1 amps - 10 hours
    2.1 amps - 5 hours
    7.3 amps -1 hour

    If it is a good one.
     
  14. netfreak

    netfreak New Member

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    @tvtech,
    I read your post but the problem is that I didnt had anything to say else than this one thing that those batteries of very good quality are pretty expensive at least for me. That is why I want to have my hands on cheap things first so at least I get to learn stuff Sir

    @ronv
    Okay thankyou thankyou :)
    & can you guide me a bit here . . . that how did you calculate this stuff. It will be really helpful to learn this from you
     
  15. colin55

    colin55 Well-Known Member

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    The /2AH infers that the battery is good for providing 1 amp for 12 hours, 2 amp for 6 hours, 3 amp for 4 hours and 6 amp for 2 hours.

    If this were the case, the battery would be able to provide 1 amp for about 18 hours and the manufacturer would be very pleased to say the battery has a capacity of 18AHr.
    The Chinese put all sorts of things on their labels.
    You will be lucky to get 12AHr out of the battery at any more than 500mA drain.
     
  16. filbo

    filbo New Member

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    Yo netfreak
    http://www.fengnengbattery.com/en/article.php?act=read&aid=11. This link will take you to a page with 6dzm12/2hr performance curves. They claim ISO9000 accreditation as well as iso14000. The curves are a bit less specific than I am used to seeing. I can't speak for or against them.

    Regards Phil
     
  17. netfreak

    netfreak New Member

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    @colin55

    Im confused a bit here. . First you said that /2AH infers that battery is good for providing 1 amp for 2 hours, 2amp for 6 hours and so on. .
    Then you said
    however above you've said that battery would provide 1amp for 2hours?

    Um if its possible then can you please make me understand on these things? I've got this 12V/12Ah/2HR battery(whose pic I have uploaded here)
    However in the market I saw a battery whose ratings were written as 12V12AH/10HR battery( but I didn't go for that as I assumed that the one I had bought would also work for 6 hours if I drew 2amp from it)

    Please tell me that how much backup would my battery(12V 12AH/2HR) give if I draw 2amps from it
    Similarly also tell me that what if I go for the battery(12V 12AH/10HR) how much would this battery had given me a backup if i had drawn the same 2amps from it?


    @filbo,
    Ihhave went through the curve :/ but I didnt get anything from that :/ I guess may be because of not having much knowledge :/
     
  18. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi netfreak,

    I would recommend you do this.

    1. Charge the battery to its full capacity.
    2. Let it stand idle for 1 hour.
    3. Use a vehicle 12V lamp, say 12Watt as a discharge load.
    4. Note the time and start to discharge the battery thru the 12V lamp.
    5. Keep checking the battery voltage as it discharges
    6. Stop the discharge and note the time when the battery reaches its permissible discharged voltage.

    This will give the 1Ahr period for your battery.

    You could repeat the above using a 12V 24Watt car bulb, this will give the 2Ahr rate period.
     
  19. colin55

    colin55 Well-Known Member

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    Firstly, I didn't say: you've said that battery would provide 1amp for 2hours?

    Let's go back to basics.

    The original rating for a battery was “14 hour rate.”

    It means the battery will deliver it rated capacity of say 12 amp-hours when it is discharged over a 14-hour period.

    In the second battery example, the battery manufacturer states his battery will deliver 12 amp-hours when discharged over a period of 10 hours.

    The first graph shown in the posting above is totally inaccurate as it is showing the capacity of their battery is the same when discharged over a period of 12 or 13 hours as it is when discharged over a period of 2 hours.
    You have already been told that this totally false however every manufacturer would love to convey that their battery will deliver its full rated energy when subjected to heavy loads.

    This is not the case. When you draw a heavy load, the capacity of the battery reduces considerably.

    As I said before, the Chinese supply data and graphs that don’t hold up to scrutiny.

    Always assume capacity is taken over a 10 to 14 hour period.
     
  20. netfreak

    netfreak New Member

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    @ericgibbs
    ok :) thanku thanku :)

    @colin55
    ahm ok sir :)
     
  21. netfreak

    netfreak New Member

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    i have got another question here now :/ related to the battery thing

    actually i have got a SLA battery whose specs are 12V 12AH/2HR

    i bought a charger for it from the shopkeeper. The charger's ratings are OUTPUT: 12V,3A
    However when i measured the output of the charger myself with DMM, I found that to be equal to 18.8V

    Now the thing is I really want to know that lets suppose my battery is low like it gives me a reading of 12.2V by DMM. So approximately how much time its gona take me to take the charge up of battery from 12.2V to 12.7V(full) by using the charger that I have? Is there some mathematical way to calculate it?
     

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