How many amps & hours to charging a battery be full

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 question, why use the lead-acid battery to power a lot of circuits.

How many amps & hours to charging a battery be full
How many amps & hours to charging a battery be full

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 battery, 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.

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?

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.

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.

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.

Battery full charging low current

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.

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