# Battery-internal-Resistance-EMT-p3

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```					                                                                                                                   Stage 1 Tasks
Measure the battery terminal voltage
(This is the voltage that the battery has
when it is not connected to a circuit and
Measuring the Internal Resistance of a Battery or Power Supply (Stage 1)                                           is not doing any work)

The terminal voltage is always higher than the on
Required for P3 Electronic Measurement and Testing                                                                 load voltage because of the internal resistance of
the battery

In this example the battery terminal voltage reads
9.3 volts. By the time I had finished the test the
battery terminal voltage had dropped to 8.9 volts.

Stage 1                                                   Basically the older and more worn out a battery is,
the higher its internal resistance and the faster its
Connect the battery to the meter as                       terminal voltage will drop.
shown. Set the range to V – DC.

Read the terminal voltage of the battery
from the display.

Battery

Voltmeter

Stage 1 Schematic
Connect a variable resistance box and an
ammeter in series with the battery.
Measuring the Internal Resistance of a Battery or Power Supply (Stage 2 & 3)                     Set the ammeter to measure mA DC

Adjust the value of the resistance box until the
current reads 0.005 Amps which is the standby
Ammeter                                                                            current of the LM386 amplifier

Read the value of the battery voltage

Calculate the value of the internal resistance
Voltmeter
R = V/I = (Terminal voltage – on load voltage)
Current drawn by circuit

Ammeter

Resistance box
Voltmeter

Resistance box
Given the internal resistance of the battery
current of the amplifier is flowing through the
circuit.

Remember on load voltage:                                  Stage 2 Schematic

Voltage = Current drawn x internal resistance

load current is flowing through this circuit.

Measure the on load voltage of the battery.

Do your calculations and measurements agree?

If not then why not?

```
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