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.
You probably already listened that to charge a battery the voltage of charging source should be greater than the battery voltage but the question is how much voltage should be greater and when will I know that you should stop charging now?
There are two questions here. Let’s answer it one by one.
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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.
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.
Which means if you have 100Ah lead acid battery then its charging current must not be greater than 100/10=10 A. So the question is how to maintain 10 A current going inwards the battery? The answer is that the internal resistance of ‘12 volts 100Ah lead acid batteries’ is adjusted in such a way that whenever you apply the voltage of 14.4 volts then the battery will automatically draw 10 Amps.
Now our question was that when should you stop the charging? You don’t have to!! If you are able to apply the constant voltage source of 14.4 volts than the battery will draw current from the source according to its need.
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.