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How to build a battery charger for 6V 4.2Ah lead acid battery?

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Slayerza

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Hi,
I have the following sealed lead acid battery
6V 4.2Ah

This battery was stripped from an old device but the charger (wall adapter) has been lost. How do I charge this battery if the following apears on the battery

CONSTANT VOLTAGE CHARGE
Cyclic Use 7.2-7.5V
Standby Use 6.75-6.9V
Initial Current <1.26A

So how do I build a charger (preferably simple) to charge this battery as I want to use it as the backup battery in my applications

Cheers
Slayer
 

Re: Battery Charger

Simply, step down the 220V AC voltage to approximately 10 V in AC using step down transformer.
Put Bridge rectifier and a electrolytic capacitor of value 10000 uF/25V to covert it to DC.
See your battery specification. Charging currtent=AH of Battery/10

Design a transistor based regulator circuit. The current rating of the series pass transistor must be meeting the "charging current" requirement +10% extra.

Still any problem, ask !
 

Re: Battery Charger

If I use a variable voltage regulator like the LM317 will it also be suitable?

Cheers
Slayer
 

Re: Battery Charger

No problem, it will work provided that the current rating of IC package should be suitable.
 

Re: Battery Charger

Hi
there is a complete coding algorithm for battery chargin on Maxim site.
If you want the simplest one do as "manojshukla" said. I think you should limit the maximum current rating to be equal to 10% of A/H rating of the battery. This is called slow charing method. It will take longer time ti fully charge the better but in another way it extends the battery life time

Thanks
BR
Haytham
 

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