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Charging Batteries using a Power Supply

Discussion in 'Power Electronics' started by Sadlercomfort, Oct 29, 2015.

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  1. Sadlercomfort

    Sadlercomfort Ash

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    Feb 9, 2013
    Hi Guys,

    Is it possible to charge two 12v, 7AH lead-acid batteries in series directly off my DC power supply?

    I was thinking maybe setting the current limit to about 3A and voltage to about 28-30V.

    Thanks,
    Ash
     
  2. Memory_Leak

    Memory_Leak

    11
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    Oct 27, 2015
    I do it all the time with motorcycle batteries. I'd recommend a lower charging voltage, something closer to 15V. Your current limit is probably fine though. Maybe you could look up some similar batteries and see what the manufacturer recommends.
     
    davenn likes this.
  3. AnalogKid

    AnalogKid

    2,483
    715
    Jun 10, 2015
    SLA batteries frequently have a recommended charging current of C/10. For a 7 Ah battery, that would mean a charging current of 0.7 A. With two identical batteries in series the current would remain at 0.7 A. Of course, the datasheet for your particular batteries might spec a different charging current.

    ak
     
  4. Sadlercomfort

    Sadlercomfort Ash

    424
    55
    Feb 9, 2013
    Are you sure 15v?

    I'm connecting these two in series, so will be a nominal 24v across the two.

    I've attached the datasheet for the battery "NP7-12FR".. I have a bad habbit of forgetting to look at datasheets.

    It states the maximum charging current is 1.75A at 14.4V-15V.


    So if I charged them at 28V, 1.75V would this be acceptable? The batteries will not be left unattended, so i can keep an eye on them.
     

    Attached Files:

  5. Alec_t

    Alec_t

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    Jul 7, 2015
    If the max specified is 1.75A I'd use something less, say 1.5A, hopefully to prolong the life of the batteries.
     
  6. Sadlercomfort

    Sadlercomfort Ash

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    Feb 9, 2013
    I agree Alec =)
     
  7. davenn

    davenn Moderator

    13,802
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    Sep 5, 2009
    in series, yes, around 26 - 27V
     
  8. Memory_Leak

    Memory_Leak

    11
    2
    Oct 27, 2015
    My bad I didn't see that they were in series. In that case your original settings sound fine to me.
     
  9. Sadlercomfort

    Sadlercomfort Ash

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    Feb 9, 2013
    Thanks guys :)
     
  10. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    So if 1.75a is recommended, does that mean the charge rate is C/4?
    If so, why so different than the C/10 rate that's normally used?
     
  11. Sadlercomfort

    Sadlercomfort Ash

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    55
    Feb 9, 2013
    Well I guess it just extends the life of the batteries. Perhaps C/10 is the recommended charge rate.

    I think the maximum charge rate is ok, but not when the batteries are almost fully charged. A sophisticated charger would charge the battery fairly quickly and limit the current as the battery comes up to full charge.

    http://www.homepower.com/articles/s...t-products/ask-experts-battery-charging-rates
     
    Last edited: Oct 31, 2015
  12. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Thanks but that doesn't really answer my question.
    That would be the maximum charge rate that the battery would draw when it's charge is depleted. As the voltage comes up during the charge the current should drop. So as it nears the end of the charge, the voltage will be around 15v and the current will be probably 1/2 amp or less.
     
  13. HellasTechn

    HellasTechn

    1,556
    215
    Apr 14, 2013

    Yes you can do that.

    What i do is i connect the batteries and slowly raise voltage from 24 volts up untill i get a reading of about 500ma at my amp meter (usually reach 26volts 13 volt per battery). then i use the current limiter set around 500-600ma.

    Remember the less charge current the better for battery lifespan.

    Pulse chargeing is the best i think but since you dont have such charger...
     
  14. AnalogKid

    AnalogKid

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    715
    Jun 10, 2015
    There are different variations of internal construction that make different manufacturers products...different. Note that "frequently" and "recommended" are qualifiers covering hundreds of products from dozens of manufacturers, not absolutes.

    The data sheet lists the max. charge rate. To Alex's excellent advice in post #5 I'll add the only applicable part of the article in post #11 - proper charging of an SLA battery requires a multi-step charging algorithm. Linear Tech makes excellent single-chips controllers for this. Maxim and Unitrode also make SLA charger controllers.

    ak
     
    Last edited: Oct 31, 2015
  15. thaers3d

    thaers3d

    5
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    Nov 7, 2015
  16. Sadlercomfort

    Sadlercomfort Ash

    424
    55
    Feb 9, 2013
    Really useful information there =) thanks
     
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