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Voltage and Current: Motors (2019)
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Voltage and Current: Motors (2019)

Failed Motor Circuit

Mini Project Larger Battery

The circuits that you have been building have used a single battery with 3.3 volts. For this project, we will combine two batteries together to create a larger battery.

Block diagram: Motor with a larger battery
Larger Battery: Required items and tools

Find the following components in your kit:

  • Two Fresh Coin Cell Batteries Two Fresh Coin Cell Batteries
  • The Motor Circuit from the previous lesson The Motor Circuit from the previous lesson
  • Digital Multimeter Digital Multimeter
Step 1: Combine batteries

Build this circuit shown here.

Step 2: Measure the voltage

Use a multimeter in voltage mode to check the voltage across the motor.

(Optional) Module: Measure the Voltage

Use the module below if you need a refresher on how to measure voltage using a multimeter.

Testing Voltage with a Multimeter: Required items and tools

To begin testing wires, you will need the following:

  • Digital Multimeter Digital Multimeter
Measuring Voltage with Multimeters

Multimeters measure voltage differently for Direct Current (DC) Circuits and Alternating Current (AC) Circuits. On a multimeter these setting are shown with different symbols:

  • AC Voltage
  • DC Voltage
Safety Notice

AC voltage can be very dangerous (especially the main voltage out of outlets on a building’s wall) and great care must be taken when measuring it with a multimeter. If you feel like you must test or measure AC, it is recommend you get a non-contact tester rather than use a digital multimeter.

Step 1: Set Multimeter to DC Voltage Mode
picture of both manual and auto ranging voltage selection

Depending on the multimeter you have you may have one setting or many different settings for DC Voltage.

auto ranging multimeter
  • An auto ranging multimeter will automatically change the the range of voltages it is measuring in to accurately measure the voltage.
manual ranging multimeter
  • With a manual selection multimeter the correct resolution must be selected to correctly measure the voltage. The settings shown on the multimeter show the maximum voltage that setting can successfully read.
Overloaded voltage measurement
  • If you select a setting that is too small for the voltage you are measuring the multimeter will display a 1 on the left-most side of the screen.
  • This means that the multimeter is overloaded or out-of-range of the voltage being measured.
Measuring a coin cell with different voltage settings
  • If you select a voltage setting that is too high, you will not have the same accuracy as if you were to use a setting that is close to the amount of measured voltage.
Step 2: Insert lead probes into the terminals
Probes in the correct ports

When measuring voltage make sure your probes are plugged into the correct ports. The Black Probe should be in "COM" or common and the Red Probe should be in the Red Port with the Voltage symbol (V)

Step 3: Measure for Voltage

When measuring voltage in a circuit it is always useful to know the voltage of your power supply, frequently with DC circuits this power supply is in the form of the battery.

Measuring voltage on coin cell
  1. Set the multimeter to the DC Voltage setting, if you have a manual selection multimeter select the 20V setting since the expected measurement is 3V.
  2. Take the positive (red) multimeter test lead and place it on the positive side of the battery.
  3. Place the black lead on the negative negative side of the battery.
  4. The multimeter should show a value around 3V.
  • What happens if you switch the nodes?
    Nothing bad happens! The reading on the multimeter is just negative. The multimeter measures voltage in relation to the common probe. The multimeter measures how much voltage is there on the ‘+’ of the battery compared to common or the negative pin. If we switch the probes, we define ‘+’ as the common or zero point making the measurement negative.
What is Voltage Drop?
Voltage drop

The multimeter can be used to test different parts of the circuit in a practice called nodal analysis. By measuring the voltage across the circuit, we can see how much voltage each component requires. In a very simple circuit such as an LED in series with a battery, the LED can be used to measure how much voltage the LED is using. This voltage is referred to as voltage drop.

Step 4: Test for Voltage Drop
[picture probing LED]

Measuring the voltage drop of component in a circuit, requires the circuit to be connected. With the LED bright and lighting up probe both legs with the multimeter. (Place the red probe on the longer leg of the LED to measure positive numbers)

This LED is using 2.74 Volts of the available 3.01 Volt supply to illuminate.

Check Your Understanding

What setting should the dial be turned to to measure DC voltage?
Hover over parts of the image and click to select
  • Voltage Setting 1
  • Voltage Setting 2
  • Resistance Setting
  • Diode / Continuity Setting
  • Hertz Setting
  • Current Setting 1
  • Current Setting 2
  • Current Setting 3
Which terminal should the RED lead be plugged into for this multimeter?
Hover over parts of the image and click to select
  • 200mA to 10A current terminal
  • The selected terminal only receives the red lead, to measure capacitance, temperature, hFE and 0.001mA to 200mA current.
  • Return terminal for all measurements
  • Voltage, resistance, frequency, diode, and continuity test terminal
Which DC voltage setting should be used to measure a voltage around 24 Volts?
Hover over parts of the image and click to select
  • 200m volts
  • 2 volts
  • 20 volts
  • 200 volts
  • 1000

What happens?

The motor spins faster than the previous circuit. The voltage across the motor should be larger than the previous circuit.

Try It: Stall the motor

What happens if you hold the spinning end now?
What happens?
  1. The voltage going to the motor is doubled, so the motor is much harder to stop. Note: Do not hold onto the motor for too long as you may injure yourself!

Explanation

The circuit now has more voltage! There is enough strength to overcome your fingers trying to stall the motor. Combining the two batteries increased the amount of voltage that is in the circuit. This allows there to be more voltage to power the motor.

Larger batteries typically are formed from multiple smaller batteries in series. For instance, this A23 battery is actually made up of several coin cell batteries:

Measure the current.Disconnect an alligator clip from one of the motor leads, and use your multimeter to measure the current going through those two points.

How much current is going through the circuit now? Is it larger or smaller than the previous, single battery circuit? With two batteries now, there is not only more voltage, but more current.

Safety: Higher voltage and higher current can be dangerous. Voltage levels higher than 50 Volts can carry a dangerous, or even fatal, amount of current!

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