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Over-charging and deep discharge protection for sla 6v battery.

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StrikeR.DbZ

New Member
Hello friends,:)

I want to build a 6v emergency/camping light of 6v sla 4.5ah battery using a 8w fluroscent tube.Thanks to hero999 at this forum i have got to light up my tube. But the part of charging the battery and protecting it from overcharge or deep discharge is still a problem just like "you are ready with your camping kit but don't have your shoe laces tied yet."

For the part of the charging i have heard about uc3906 as a "sla linear charger blah blah..." and for deep discharge protection i don't even have a clue what to do.

So if any could show some way, like giving a circuit diagram for these processes and a brief of explanation of how the circuits work would be great.

Thanks in advance.....
 

Tedfred

New Member
I do maintenance of many off the grid solar systems. The optimum word here is emergency backup battery. I an assuming that this light is only used from time time. First of all you can’t over charge a battery, that is say put more current in to it than it can hold. In simple when a battery is fully charge, it is fully charged, And that’s it. Any more attempt to raise the charge is hopeless. It is just turned to heat and short life the battery. No matter the charger. So the term over charging just means heating up the battery. A simple trickle charger or low current charger will do the job. The PWM charger and other are make for multiple cell battery that are use a lot and that may have unexpected heavy discharge . These chargers can equalize the weaker cells and bring then up to full charge by doing what is called a bulk charge. But that is more that you need to know.
 

StrikeR.DbZ

New Member
Thanks for the reply Tedfred and when i posted this question and nobody replied for a long time i did make a trickle low current charger off a 9v supply and 7808 with 2W 2.2ohm current limiting resistor, and it works well. Fewdays ago i bought a 10v 4.5+/-0.5 v solar panel and connected it a dc socket which is directly to the battery and i am charging through it. Anyway its always exciting to start building something new.
 

RCinFLA

Well-Known Member
For a gel cell, you can permanently float it at 6.6 to 6.8 vdc.

Simplest charger would be LM317 reg from a 10vdc to 12vdc power pack. Make regulator 0.65 v higher (7.4vdc) and put a blocking diode between regulator and battery to prevent discharging battery when charger is unpowered. You will need a heat sink on LM317. Keep in mind the 2.5 vdc minimum drop across LM317 for your power pack minimum voltage.

An 8v regulator through a series resistor will ruin battery if left permanently on battery.
 
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StrikeR.DbZ

New Member
I don't leave it charging forever its actually used ocassionally while camping or travelling so it is charged ocassionally but i wanted to make a completely automatic charging circuit using some ic i heard about like uc3906 that automatically manages the charging voltage current and time as it is preset. But i could not get much info about it, if I could get some circuit diagram to know how to make such a charger it would be great.
 
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