How to Find the Charging Current of a Battery

To charge battery safely we need right amount of electricity like current.

It is the same like plant needs right water.

Most people use multimeter to check this but not everyone has it.

In this article for How to Find the Charging Current of a Battery is easy trick without tool:

• It uses one small part called a resistor.
• Put resistor in charging circuit.
• When battery is charging the resistor gets warm.
• More warm means more electricity going.

Circuit Working:

Parts List:

This circuit shows smart way to check charging current without multimeter.

Just put 22 ohm 2 watt resistor in series with battery.

Touch it to feel the heat.

If it is very hot then current should be 100mA or more.

We used 2 watt resistor to feel the heat.

Heat means lost energy in which bigger resistor helps reduce loss.

To know how hot 2 watt feels try 560 ohm 2 watt resistor on battery.

It gives 250mW heat and use this as example.

A 12V 1.2Ah battery has 14 watts energy.

If charge rate is 1 watt full charge needs around 16 hours.

This circuit is good for many things like car solar charger or pulsed solar charge.

Also it works like safety and it limits current to 100mA.

If current goes above 130mA then resistor gets hot and smelly.

If we remove the 22 ohm resistor then current will go higher.

Increase can be small to 10% or big to 100% or more like when using car cigarette lighter socket.

Formulas and Calculations:

In this circuit charging current (I) can be found using this formula:

I = C / t

where:

• I is the charging current in amps
• C is the battery capacity in Ah
• t is the charging time in hours

So divide battery capacity by time to get charging current.

How to use this in real circuit:

First check battery label or datasheet to find amp-hour AH.

Then decide how long we want to charge it means in hours.

Also check the chargers max current.

Example:

Charger gives max 5A.

Battery is 12V 50Ah.

We want to charge in 10 hours.

I = 50Ah / 10h = 5A

Since 5A is within chargers limit then its okay.

Note:

This is simple math but in real charging is not always exact.

Chargers often have voltage control to stop overcharging.

This can change current while charging.

For best results and safety always check battery and charger datasheet.

How to Build:

Steps to follow How to Find the Charging Current of a Battery which are mentioned below:

Series Resistor Setup:

• Connect 22 ohm 2 watt resistor in series with battery positive.
• Battery negative goes straight to chargers negative.

Charging Time:

• Check battery power and charging rate.
• If we are charging at 1 watt and battery is 12V then 1.2Ah which is about 14 watts
• Then full charge takes about 16 hours.

Safety Circuit:

• Resistor also acts like safety.
• It limits current to 100mA.
• If current goes above 130mA then resistor gets hot and smelly with warning sign.

Adjustments:

• If we remove the 22 ohm resistor then current increases.
• How much it increases depends on the charger.

Note:

• Be careful when working with circuits.
• Heat and current can be risky.

Conclusion:

In this post for How to Find the Charging Current of a Battery using 22 ohm resistor and feeling its heat, we can guess charging current without multimeter.

This trick is easy, useful and helps us learn how current flows in charging circuits.

References:

Battery charge current