How many amps do the battery need to charge? And how many hours does it charge? The battery will be full. How to extend battery life 2-3 times longer. First of all, some may have questioned, why use the lead-acid battery to power a lot of circuits.
Imagine you are going to create an Emergency light. We always choose a 12V battery because this voltage is very popular. We can easily find the load device (12V lamp).
Why use Lead-acid Battery
And compare between lead-acid batteries and other types of batteries, such as 1.2V Ni-MH batteries, 10 batteries.
We will choose lead-acid batteries because they are easier to use and cheaper. And they provide enough electricity, in basic use.
We know that when we run out of battery power. It can be recharged many times. And it has a normal service life of about 2 years (according to my experience).
Many people wonder how to charge it.
- If you are beginner Learn more in simple
Principles of correct battery charging
First of all, I must say that Principles of car battery charging and motorcycle battery charging. Use the same charging principle. Factors to consider include:
- Battery capacity Ah
- Remaining battery capacity before charging. How much is left?
Recommended: Recycle Free Li-ion battery from E-waste
How many amps do the battery need to charge?
First, we have to look at what size of capacity is our battery. It has units of Ah. See the example battery that I use. It is a 12V 3Ah size. It is in a small motorcycle.
I got this battery for free from my brother. Which runs a motorcycle repair shop. He said that the owner of the motorcycle will replace it when the battery is about 1 year old. Which we can still use for another 2 years. And maintain a constant charge.
I use this size because it is enough for small electronics. Such as a solar cell system in the garden. So you can imagine using LED light bulb 12V 2W (0.16A).
This light bulb will light up for long about 3A/0.16A = 18 h. Is it nice?
Anyways, To charge your car and motorcycle batteries properly. We should charge a low current and a long period. So it will be good for the battery.
Should not be charged with high current To make the battery full quickly. This can result in the battery overheating, deterioration, or swelling.
On the battery, the manufacturer will recommend a charging Method.
- Standard(low current): 0.3A for 5 to 10h
- Quick (high current): 3A for 0.5h
So, I charge with 0.3A of current for 10h to 12h to full.
LEARN: Relationship Between Current and Voltage
Calculation method
Current to be charged = 0.1 x battery capacity (Ah)
For example
- Motorcycle battery, 12V 5Ah: 0.1 x 5 = 0.5A. So it should be charged with a current of 0.5 A.
- Car battery, 12V 65Ah: 0.1 x 65 = 6.5A. So it should be charged with a current of 6.5 A.
- Car battery, 12V 65Ah: 0.1 x 100 = 10A. So it should be charged with a current of 10 A.
Note
Most of my circuits are suitable for small batteries below 10Ah. Because they charge only as low as 1A. Some people need to charge larger batteries. Therefore requires a very high charging current than 10A. Therefore not working The circuit must be specially designed.
How many a charged voltage?
Usually 12V car battery and 12V motorcycle battery have 2 charging modes.
- Float charge (stand-by use) is charging at 13.6-13.8V.
- Equal charge (cycle use) is charging at a voltage of 14.2-14.9V.
In conclusion, it should be used with a voltage of no more than 15V and if it is lower than 13V, the charging will not be good.
How many hours to charge the battery?
See the graphs on the datasheet of our battery model. Most of the time when the battery is discharged. There will be about 35% Ah battery capacity left. Therefore, it needs to be charged an additional 65% to make the battery full.
Calculation method
Additional Ah amount = 65% x battery size (Ah)
Charge hours = amount of Ah to be supplied ÷ current that should be stored
For example
- Motorcycle battery 12V 5Ah
Amount of Ah to be charged = 0.65 x 5 Ah = 3.25 Ah
Charge hours = 3.25Ah ÷ 0.5A = 6.5 hrs ≈ 7 hrs.
Refers to the 12V 5Ah motorcycle battery when the battery is dead. We should charge an additional 3.25Ah by charging with 0.5A current for about 7 hours.
- Motorcycle battery 12V 5Ah
Amount of Ah to be charged = 0.65 x 3 Ah = 1.95 Ah
Charge hours = 1.95Ah ÷ 0.3A = 6.5 hrs ≈ 7 hrs.
Refers to the 12V 5Ah motorcycle battery when the battery is dead. We should charge an additional 3.25Ah by charging with 0.5A current for about 7 hours.
All in all, it should take about 7 hours to charge.
When to charge the battery
We know the battery should be charged. When it has a low capacity of about 35%.
But how do we know that we have reached that point? Of course, usually, the manufacturer will always tell you. Look at the battery.
This battery is filled with acid. If we measure the stabilized open circuit or its voltage is below 12.4V. This needs charging.
If you leave it, do not charge the battery. It will cause that battery to continue to deteriorate.
Make Gel cell battery charger circuit
How to see that the battery is fully charged?
Normally when the battery is fully charged. It will have a higher voltage than 12.4V, roughly equal to the output voltage of the battery charger. See the picture below.
In normal (old age) battery chargers there will be the Ammeter connected in series between the battery and the battery charger.
When the battery is almost full. The current will gradually descend near zero. Because both voltages are almost the same. Until the current flows less.
Due to the V = IR rule, if the charging voltage V increases. It will cause the charging current (I)to decrease.
In modern battery charging circuits, The battery voltage will be measured. When the voltage is indicated that the battery is fully charged. The system will automatically cut off the power more convenient.
Automatic battery charger circuit
In my experience In case of emergency or need to save. We can use simple circuits, for example.
It charges with low current and the voltage does not exceed 15V. We set the alarm for 7 hours or 10 hours. At the time we set. The battery is fully charged normally.
Related Posts
I love electronics. I have been learning about them through creating simple electronic circuits or small projects. And now I am also having my children do the same. Nevertheless, I hope you found the experiences we shared on this site useful and fulfilling.
Kindly issue hobby electronic circuits.
Hello Ashim Kumar Sen,
Thanks for visiting. It is a great idea. I love hobby electronics circuits, too. I will try it. Please follows me.
Thank you Apichet for your wealth of information that is very helpful and educational, I follow all your circuits and try and test them when ever possible.
I have been involved in electronics for over 55 years, but I am still learning with your help.
Keep up the good work.
I am very happy to read your message. I appreciate your continued interest in electronics. I think retirement age is a golden opportunity to learn and create hobbies.
My children and I will continue to do this work.
Thank you for your continued reading.