7Ah Sealed lead acid battery is a very popular battery which people use in most places like fans, LEDs etc. The reason behind popularity of 7Ah battery is due to its medium size and medium Ah rating. By medium means, its size and ratings lies between the small batteries and large batteries. For medium purposes, the size and rating of battery is ideal.
For example if you want to glow a 20Watt LED then this battery will serves the purpose really well.Before go further, studying the articles related to battery basics, rechargeable batteries and non- rechargeable batteries would be fruitful. Here we will design a 7 Ah charger for this battery.
How to Charge a Battery
How much source voltage should be greater than the battery voltage to charge?
It’s not a single value that you can rely on. But an average value at which you can surely charge your battery without hesitation is 20% more voltage than the battery voltage.
For example in the case of 12 volt battery: 20% x 12 = 2.4
So, charging voltage source should be: 12+ 2.4 =14.4 volts
To charge a 12 volt battery the charging source should be 14.4 volts. Now the question is that how to attain this volts. I will answer this question later.
When Should you Stop Charging?
During building a charger, the most important question comes in mind that when should I cut off the charging source. This is the very critical point during making automatic chargers because mostly batteries do not bear overcharging and their life drastically decreases due to overcharging. Before I answer this question first understand anot should be charge at C/10 current no matter how big the battery is.
For example in 100Ah battery, if the battery is fully discharged then it will take 10Amps from the 14.4 volts source and if the battery is fully charged then it will not draw any current from the source and at 50% charging it will draw 5amps from source.
Now I think you are able to understand the procedure of making an automatic charger for sealed lead acid batteries. You can apply this procedure for any sealed lead acid battery but the charging source should be big enough to give the required current to the battery.