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
                                                                                                 Stage 2 Tasks
                                                                                                 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


                                              Stage 3 Tasks
                                                                                                                                                    Resistance box
                                              Given the internal resistance of the battery
                                              calculate the on load voltage when the full load
                                              current of the amplifier is flowing through the
                                              circuit.

                                              Remember on load voltage:                                  Stage 2 Schematic

                                              Voltage = Current drawn x internal resistance

                                              Now adjust your resistance box so that the full
                                              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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posted:10/6/2012
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