Charging a 12v SLA VRLA battery for DC lighting system!

Discussion in 'Power Electronics' started by Ujwal Bhagat, Jul 1, 2016.

  1. Ujwal Bhagat

    Thread Starter Member

    Jan 30, 2016
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    Hey, guys I'm back with a new project. My previous project didn't work out well, so now I have more practically possible concept, or I can say I have already build it!.
    Now I have made a DC emergency lighting system, when the power goes out it should provide a backup of 4hours.
    Specifications:
    Battery: 12v 5AH SLA VRLA type
    Load: Two modified led bulbs requiring 32- 36v each, connected in parallel. Gives good brightness at 500ma each, so total 1amp.
    Regulator:XL6009 DC TO DC booster https://www.amazon.in/gp/aw/d/B00HV59922/ref=ya_aw_od_pi?ie=UTF8&psc=1
    • Low ultra wide input voltage 3 v ~ 32 v, the best is 5 ~ 32 v working voltage range;
    • Low ultra wide output voltage 5 v ~ 35 v;
    • Built-in 4 a efficient MOSFET switch tube, make efficiency up to 94%; (LM2577 current only 3 a)
    • High switching frequency, 400 KHZ, can use the small capacity of the filter capacitor can achieve very good effect, ripple smaller and smaller
    • Can handle load upto 4 amps.
    Now my question is, can I float charge my battery on 13.05v for how much time?
    How much backup time will I get?
    Any suggestions on my current setup?
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Float charge is for an indefinite time, i.e 'for ever'.
    13.05V seems rather low. What does your battery manufacturer recommend?
     
  3. Ujwal Bhagat

    Thread Starter Member

    Jan 30, 2016
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    I don't know since I don't have a manual of the battery. It is from POWERZONE brand(Indian)
     
  4. Ujwal Bhagat

    Thread Starter Member

    Jan 30, 2016
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    One thing should be considered, the voltage of the battery gradually drops below 11v, on 1amp load.
    After 15 minutes, without load it reads 12.50. Is it normal?
    To charge the battery, I'm using a ac to DC adapter and the same regulator to boost 12v at 600ma to 13.65 to charge and 13.05 to float.
    The battery takes 100ma while charging and on float also.
     
  5. Ujwal Bhagat

    Thread Starter Member

    Jan 30, 2016
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  6. Ujwal Bhagat

    Thread Starter Member

    Jan 30, 2016
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  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    That's a poor battery, or it needs re-charging.
    I can't comment on the linked battery as I have never used that brand.
     
  8. Seth Schaffer

    New Member

    Jun 8, 2016
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    From what I know about SLA battery systems, that battery should work fine. Keep in mind though, ideally you want your float charge voltage to be in the range indicated in the "standby" segment of the battery label. In this case, 13.6-13.8 volts.A drop of over a volt from less than 2 amps current draw seems excessive to me so I'm guessing if that's what you saw on the other battery, it is likely a very poor quality battery.

    The 12V 600mA boosted up to 13.7 volts will definitely give you a good current level for float charging, as you want < 0.1 (capacity in Ah) or < 0.72 A with that battery, and you'll be getting .5-.6A.

    However, assuming you are using the same voltage boost board to bring that battery voltage from 12V up to 36V, that booster will only get up to 35V or so. It might work, or it might not. My best guess is that it will, but you'll have to see for yourself. Since at the extrema of the range the boost board can produce it runs less efficiently, you also may want to consider making sure the heat is dissipated from the board powering the lights. The other should be fine.
     
  9. Ujwal Bhagat

    Thread Starter Member

    Jan 30, 2016
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    Yeah, I too think it is time to buy a new battery, but why my battery is taking only 0.100amp while charging or on float.
     
  10. Seth Schaffer

    New Member

    Jun 8, 2016
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    Honestly, I'm not too sure what's causing that. I suggest you bring the charge voltage up to 13.8 volts and measure the current again from there. If the battery voltage is too close to the charge voltage, there will be almost no current flow.
     
  11. hp1729

    Well-Known Member

    Nov 23, 2015
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    Doing much the same thing here but my LEDs are bigger. I have some that pull about 1 Amp at 9 to 12 V and another that pulls about 2 Amps at 18 to 24 Volts. For the larger I just use two batteries. Yes, float charge at 75 to 100 mA. General charging at about 1 Amp. It draws more current early in the charging cycle and less towards the end. 13.4 to 13.8 V, where ever it tops out at.

    I charge the batteries at the bench and in the assembly it gets just a 75 mA float charge. On power loss a switch turns the light on. I only expect a few hours of use, then long term slow charge.
     
  12. Ujwal Bhagat

    Thread Starter Member

    Jan 30, 2016
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    I am following a chart on battery university website which indicates that 12.55 volt in an open circuit indicates 80% charged battery!
    I want to are the specifications are good for my requirements of my loads.
    Thanks for reply.
     
  13. Ujwal Bhagat

    Thread Starter Member

    Jan 30, 2016
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    I will try again. My multimeter battery is almost dead, gonna buy new 9v bats.
     
  14. Ujwal Bhagat

    Thread Starter Member

    Jan 30, 2016
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    How much backup are you getting?
    What is the battery capacity?
     
  15. hp1729

    Well-Known Member

    Nov 23, 2015
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    Batteries are NPX-25. I'm not sure of the specs but about 6 Ahr looks about right. About 3.5" x 2.75" x 3.5" tall.
     
  16. Ujwal Bhagat

    Thread Starter Member

    Jan 30, 2016
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    How much did you pay for them?
    I can get a 7.2ah battery at 800inr!
     
  17. hp1729

    Well-Known Member

    Nov 23, 2015
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    I paid nothing for them. They were battery backup for the computer system at work. They replaced the assembly and discarded the old one. The LEDs are bought surplus, Electronic Goldmine.
     
  18. Ujwal Bhagat

    Thread Starter Member

    Jan 30, 2016
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    At that or more than that voltage also it is drawing 0.100ma, but now the it has decreased to 0.01ma. I guss the battery is fully charged!
     
  19. hp1729

    Well-Known Member

    Nov 23, 2015
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    Agreed on that. All you need to do is keep it from self-discharging. I couldn't find a proper spec for how much is a good "float" value. It looks like we came to about the same conclusion. I started with 100 mA, then later brought that down to 75 mA just to keep the stress off the LM317LZ I was using to set the voltage.
     
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