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Lead acid battery

Discussion in 'General Electronics Discussion' started by Karthik rajagopal, Apr 26, 2019.

  1. Karthik rajagopal

    Karthik rajagopal

    173
    4
    May 9, 2016
    Hi all,
    I recently bought a lead acid battery (6v, 4.5Ah)for my rechargeable lamp. I started building an auto cut off charger for my battery. I noticed that there were some data on the battery . IMG_20190426_223900.JPG
    What does cyclic use and standby use mean? Does that indicate the charging voltage or should I charge the battery till that voltage based on my use? What does the 0.15c mean?
    As far as I understood from few websites, 0.15c indicates the charging current . So if I am right, the charging current must be around 0.675A for my 4.5Ah battery . Please provide me clarity on this.
    Thanks in advance .
     
  2. Externet

    Externet

    694
    142
    Aug 24, 2009
    Cyclic means the battery supplies power often to something; as an example; a shaving machine, a nightly operated lamp...
    Stand-by is when used only in sporadic situations, like a uninterruptible power supply, an exit emergency lamp when power fails...
    0.15C means to be charged at 0.15 times the current rating figure (0.15 x 4.5Ah= 675mA)
     
  3. Bluejets

    Bluejets

    3,297
    652
    Oct 5, 2014
    Notice it says "initial current".
    This does not mean set up some diy gear to charge 675mA forever as it will certainly cook the battery in no time.

    I would advise you go out and buy a small "smart charger" that will monitor the state and adjust accordingly.
    Being 6V they may not be as vastly available as 12v however they do exist.
     
    davenn likes this.
  4. Ylli

    Ylli

    176
    28
    Jun 19, 2018
    Standby use would be for something like emergency lighting. For that type of applicationm the battery is generally keep on a 'float charge' to keep it in it's fully charged state at all times. That float voltage must be high enough to keep the battery charged, but low enough so that it doesn't boil away the electrolyte. Between 2.25 and 2.3 volts per cell is typical. The 'initial current' would mean that you would want to the charger to be current limited at 0.15 * 4.5 = 0.675 amps.

    Cyclic use is when the battery is used to power something for a length of time and then recharged - over and over and over again. Such as if you were powering a trolling motor on your boat and then recharging the battery when you got back home. In that application, you can charge at a rate not to exceed 0.25 * 4.5 = 1.125 amps until the battery reaches a voltage of 7.2 - 7.5 volts. Then you should maintain the terminal voltage to not exceed 7.5 volts until the battery is fully charged. [When will the battery be fully charged you ask? Well, that is the purpose of the smart charger. Otherwise, charge times will be in the 6-8 hour range or until the battery starts to feel warm]
     
  5. Karthik rajagopal

    Karthik rajagopal

    173
    4
    May 9, 2016
    So in stand by use , should I charge the battery till it reaches 6.7v? Or is that the charging voltage ? As far as I have understood ,my auto cut off charger must disconnect it when it reaches a voltage of 6.7v. Plz correct me if I am wrong.
     
  6. Karthik rajagopal

    Karthik rajagopal

    173
    4
    May 9, 2016
    I can't use a charger in this case as my circuit must fit into my emergency lamp. So, decided to build a cut off charger for which I must know the maximum voltage up-to which a battery can charge in stand by use. In few websites they say that a 12v battery must be charged till 13.3v but didn't find any thing like that for my 6v battery . When I bought this battery, it was charged up-to 6.4v. So I thought that charging it above this voltage can destroy the battery .
     
  7. Ylli

    Ylli

    176
    28
    Jun 19, 2018
    If it will be left on charge continuously, set your voltage limit to 6.75 - 6.90 volts. If it is going to be used regularly, recharge to 7.2 - 7.5 volts and hold it there for a couple hours - then remove the charging source..

    or, you can recharge at the higher current rate until the battery reaches 7.5 volts, then drop the charging voltage to the float value of 6.75 - 6.9 volts and hold it there indefinitely.
     
  8. Karthik rajagopal

    Karthik rajagopal

    173
    4
    May 9, 2016
    Thank you so much . One last question- in float should the voltage be maintained a constant and leave the current to vary according to the battery needs ?
     
  9. Ylli

    Ylli

    176
    28
    Jun 19, 2018
    Yes.
     
  10. Karthik rajagopal

    Karthik rajagopal

    173
    4
    May 9, 2016
    Thank you so much !
     
  11. WHONOES

    WHONOES

    623
    120
    May 20, 2017
    Charging a sealed lead acid battery is done in a particular way. It is a 3 stage process. It starts with constant current charging then it switches to constant voltage charge then when charge current drops it switches to maintenance mode.
    This sounds horribly complicated but it's not. The circuitry is quite simple.
    The constant current should be set to 25% of the battery capacity. Constant voltage charge is set to 2.35 volts per cell and the maintenance charge is set to 2.25 volts per cell.
     
  12. Karthik rajagopal

    Karthik rajagopal

    173
    4
    May 9, 2016
    What if I charge it with a constant voltage source right from the initial charge till it gets full? Will that reduce the battery life?
     
  13. WHONOES

    WHONOES

    623
    120
    May 20, 2017
    You need to limit the charge current to no more than 25% of the battery's capacity otherwise you will cause irreparable damage. It will overheat and may explode.
     
  14. dick56

    dick56

    18
    2
    Apr 15, 2011
    Also, constant current charging is better because it will equalize all the cells or close to equalizing all the cells. You would want your constant current charge to get the battery to 6.90 volts for your emergency use lamp. When using constant voltage charging, any weak cells just get weaker as the voltage goes to the good cells, and eventually sulfation will kill the battery..
     
  15. Karthik rajagopal

    Karthik rajagopal

    173
    4
    May 9, 2016
    Thank you for your reply . I am going to charge my 4.5Ah battery with a current of 600mA.
     
  16. Karthik rajagopal

    Karthik rajagopal

    173
    4
    May 9, 2016
    I don't have a smart charger . We don't get them here too. So if I have to use a charger like that ,I must build one on my own . It would be helpful if you can send me a circuit for that .
    Thanks
     
  17. dick56

    dick56

    18
    2
    Apr 15, 2011
  18. Karthik rajagopal

    Karthik rajagopal

    173
    4
    May 9, 2016
    That's quite big. I was planning to fit my circuit within a small box. I started to design a circuit for constant current source using lm317 but faced a problem in switching it to constant voltage source automatically once the battery was full.
     
  19. Bluejets

    Bluejets

    3,297
    652
    Oct 5, 2014
    Yes, I agree.

    Pretty much anything one needs to know about charging batteries can be found at Battery University.
    Below is a typical search within their site for charging lead acid.
    https://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

    You may want to look at how to use a pre-made module similar to shown in the video below.
    Hope this helps.

     
  20. Karthik rajagopal

    Karthik rajagopal

    173
    4
    May 9, 2016
    Actually I was having this module but didn't know that it can limit the current after the battery has reached the full charge.Thanks for the help.
     
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