How to calculate AH of a battery using multimeter ?

AH calculation using multimeter

First of all in order to calculate AH of a battery, we must know about it.

AH – it is Amp-hour, one the battery energy capacity units. Which is equal to the multiplication of the continuous current (in ampere) supplied to battery while charging (at the time of charging it) / while discharging(at the time of discharging it) multiplied by the charge/discharge time.

Battery AH calculating formula :

Here current means DC current not AC, please make a note.

Battery capacity = Ampere X Hour

where for calculating capacity filled in battery ,

= Continuous charging current (in Amps) x time taken till full charge (in Hours)

where for calculating capacity given out by battery ,

= Continuous discharging current (in Amps) x time taken till full discharge (in Hours)

You can use any of the above cycle to calculate battery AH according to your feasibility.

Practical example :

In most of the cases capacity is written on the battery itself, about the capacity of battery and with different conditions. Some of them marked as 1C, 0.5C, 0.8C .

Considering that you already have a charger for your battery. Read the current in ampere which is written on the battery charger . Let us assume it says 10 Amps.

Instruments which can be used to measured exact current flowing are:

1. Multimeter (here must read current on it, to avoid any damage)

Multimeter shown with DC ampere limit (Click image to buy it)

2. Clamp-meter

Clamp-meter (Click image to buy it)

1. Calculating battery AH using multimeter:

If your charger says more than 10 Amp, you cannot use multimeter for ampere measurement more than 10 amp as said in image above. It is suitable for lesser DC ampere measurements.

Still here we will set up the connection for calculating AH using multimeter for lesser ampere. Make connections as shown below in image:

Current (Ampere) measurement using multimeter
  1. Make connections according to the image above.
  2. Note down the time (let us say it 14:54) and start the charger.
  3. Now from the multimeter you can note down the reading of charging current. You may also take multiple ampere readings during whole charging process and find out average of it.
  4. Wait till the battery gets fully charged.
  5. Now assuming the battery gets fully charged at 16:06.
  6. Now using our formula :

Battery capacity = Ampere(in ampere) x Hour (in hours)

here, ampere is 8.8 Amp or take average.

and time is 16:06 minus 14:54 which comes out to be 1 hour and 12 minutes .

Convert minutes into hours ( 12minutes/60 ) , here it is 0.2 hour.

So total time taken battery to get fully charge is 1.02 hours. And using formula.

Battery capacity = 8.8 X 1.02 = 8.976 AH

Therefore, your battery capacity comes out to be 8.976 AH (approx.)

***for exact calculation higher grade instruments are used***

2. Calculating battery AH using clamp-meter:

Here you get advantage of reading higher current flow in the wires. If your battery is of higher rating it is still safe to measure current unlike in the case of multimeter. Using clamp-meter does not require wires to get connected to it .

Make connection as shown in image below:

Current (Ampere) measurement using clamp-meter

First of all set clamp-meter to DC current mode.

  1. Make connections according to the image above.
  2. Note down the time (let us say it 13:30) and start the charger.
  3. Now from the multimeter you can note down the reading of charging current. You may also take multiple ampere readings during whole charging process and find out average of it.
  4. Wait till the battery gets fully charged.
  5. Now assuming the battery gets fully charged at 15:45.
  6. Now using our formula :

Battery capacity = Ampere(in ampere) x Hour (in hours)

here, ampere is 32 Amp or take average.

and time is 15:45 minus 13:30 which comes out to be 2 hour and 15 minutes .

Convert minutes into hours ( 15minutes/60 ) , here it is 0.25 hour.

So total time taken battery to get fully charge is 2.25 hours. And using formula.

Battery capacity = 32 X 2.25 = 72 AH

Therefore, your battery capacity comes out to be 72 AH (approx.)

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