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Lead acid battery charger.

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The battery won't charge with 12V. You'd need to provide about 13.5V to 14.5V to charge the battery. The charging current depends on charging voltage. To get it started, you could place 3 1N4007 diodes in series between the 7812 ground and the circuit/battery ground. That should give an output of approximately 12+0.7X3 = 14.1V. Or you can use 2 diodes and get an output of 13.4V. This output can provide maximum 1A current. So, you can probably only charge a standard 7Ah to 8 Ah lead acid battery.

You need to tell us the capacity of the battery first. That would dictate whether the circuit will work or not and the rate of charging.

Hope this helps.
Tahmid.
 
If you want a long life for the battery, the charging voltage should be 13.8V at 25 deg C.
 

to what voltage can a Lead Acid battery be discharged without damaging it ?
A fully charged battery has 14.2 Volts
how can we achieve that with 13.8 volts of charging voltage ?
 

sometime I got a % view of lead battery but can't find it but mean while you can count the cill and look at this volt per cell figure in the link good site to check out

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and in the diagram shot be a current limiter before the battery so it kill the voltage regulator. You can use ohm Low to calculate the current, and there is not an current limiter in the 78cxx type so it will burn or get hot if it have to draw to much current
 

What this Ah means? I should give some more voltage and current right? Could you please give the circuit diagram?

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What this Ah means? I should give some more voltage and current right? Could you please give the circuit diagram?
 

**broken link removed** where Q1 D2 and R2 is the current limiter ... use larger component they can handle more Amp for you lead Battery

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What this Ah means? I should give some more voltage and current right? Could you please give the circuit diagram?

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What this Ah means? I should give some more voltage and current right? Could you please give the circuit diagram?

Ah is Ampere-Hour. This is representative of the capacity of the battery.
http://overlandresource.com/what-is-an-amp-hour-and-how-to-calculate-battery-capacity

What is the rating of your battery?

Here are 2 circuits you may use:
**broken link removed**
**broken link removed**

Also, take a look here:
http://talkingelectronics.com/projects/BatteryCharger-12vSLA/BatteryCharger-12vSLA.html
http://www.aaroncake.net/circuits/charger2.asp
**broken link removed**
**broken link removed**

Hope this helps.
Tahmid.
 

to what voltage can a Lead Acid battery be discharged without damaging it ?
A fully charged battery has 14.2 Volts
how can we achieve that with 13.8 volts of charging voltage ?

Full lead acid (6 cells) have 12,72V-12,73V at 25C, measured 24h after charging. This value is for good new batteries.
Voltage of 14,2V can be used for charging in starting phase of charging, considering that battery is empty and need charging. If you supply 14,2V to full battery you can do lots of bad things for battery.

For my thinking based on my expirience, best lead acid charger is float charge 13,5V-13,8V (depence from ambient temp) with current control up to C/10.


Its possible to charge fully lead acid 12V from 12V source, I use this several times and works nice, I charge battery from another battery, but this is not good concept for your needs, you need real nice charger. That circuit used charge pump and is very simple with few parts with efficiency of 80%. Using this you can recharge some battery of some dislocated and isolated alarm solar system just with carrying one fully charged lead acid battery.

See this :

12V Battery Charger from 12V.jpeg

Please, do not get me wrong I just post this to show this is possible. Better make some nice regular charger with uC control. If you need circuit just say.

You can make simple and good charger with nice and reliable linear adjustable voltage regulator LM338K 5A limiting current. Just get 18V trafo, also not wrong 22V or 24V, because regulator can achieve full dissipation and full current of 5A with 10V differences Vo-Vi (24V-13,8V=10,2V). Of course good heatsink is needed, use one from PC CPU heatsink (Athlon, Duron) together with cooler. Or you can use LM350 for 3A or LM317 for 1,5A. You can add to this some LCD panel with charging data, like voltage, amperage, delivered ampere/hour, and resistance of circuit (good to monitor internal resistance of lead acid battery):

DIP_lcd_res_capa_litle.jpg

to what voltage can a Lead Acid battery be discharged without damaging it ?

OCV (Open Connected Voltage) for starter lead acid batteries lower voltage level is 11,7V-11,9V for 6 cells together or 1,95V per cell. Voltage at load when fully discharged 10,5V. If you measure OCV 10,5V you kill your battery like rabbit.
When you deeply discharge your battery (300-500 times starter in best way - best manufacturer declaration!) starting charging current in first phase should be C/20. Starter lead acid is not designed to cycling its float batteries designed for discharging for max 30-40%.

Deep cycle lead acid battery is different story for all aspects, charging, discharging, cycling, voltage levels, pricing,....
 
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