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

Failed Motor Circuit: Insufficient Voltage

Mini Project Motor Strength

In this project, you will investigate how a motor reacts to being powered by the coin cell battery.

Block Diagram: Motor connected to battery
Motor Strength: Required items and tools

Find the following components in your kit:

  • A Fresh Coin Cell Battery A Fresh Coin Cell Battery
  • A 6V motor with the red and black cable A 6V motor with the red and black cable
  • Electrical tape (any color) Electrical tape (any color)
  • 2 Wires: red and black 2 Wires: red and black
  • 2 Alligator clips 2 Alligator clips
  • Alligator Clip Crimper Alligator Clip Crimper
  • Wire Stripper Wire Stripper
Step 1: Create wires

Create two wires: one red and one black. Each wire should have an alligator clip crimped onto one end.

(Optional) Module: Prepare Alligator Clips

Follow along with this module to prepare wires with alligator clips.

Alligator Clip Connector: Required items and tools

To begin crimping clips, you will need the following:

  • Alligator Clip Alligator Clip
  • Wire Wire
  • Alligator Clip Crimper Alligator Clip Crimper
  • Wire Stripper Wire Stripper
Step 1: Prepare wire for alligator clip

Take the end of the wire, and make sure there is enough conductor exposed to attach the connector -- about 1 cm, or half an inch is good for this type of clip.

  • If you need to expose more conductor, use a wire cutter.
  • If you have a wire cutter with gauge holes, find the hole that matches the size of wire you have, place the wire through the hole, and squeeze the handle firmly. Twist the wire back and forth until the insulator is cut, and the conductor slides out smoothly.
  • If you have a wire cutter without gauge holes, place the cutting head where you want to trim to, and cut "around" the outside by squeezing the blade down gently on the outside of the insulator, and rotating the blade and wire back and forth to saw through the insulation without damaging the conductor inside.
  • If you have too much conductor, use a wire cutter to cut off the excess length.
Step 2: Insert conductive core into alligator clip

Insert the exposed conductor through the small loop on the back of the alligator clip.

Note: If the connection is too loose, strip off some more of the insulator and fold the conductor together to create an extra "thick" wire for the alligator clip slot.

Tip: Twist the ends of the conductor strands so they stay together more easily.

Step 3: Insert clip and wire into crimper slot

Insert the loop + conductor into the slot on your crimper that matches the size of the loop.

Step 4: Crimp the connection

Firmly squeeze the handle of the crimper to press the loop closed around the conductor. Many crimper designs will not open back up until you have squeezed far enough -- if the crimper won't open, keep squeezing until it does.

Tip: You can squeeze harder if you grip toward the ends of the handles.

Tip: If you really need the crimper to open early, there is usually a small release latch inside the handle.

Step 5: Crimp both sides

To ensure the fit is good on all sides, rotate the connector 90 degrees, and squeeze the handle closed again.

Step 6: Complete alligator clip crimping

The alligator head connector should now be securely attached to your wire!

Step 2: Connect wires to the battery

Using electrical tape, connect the open end of the red wire to the positive side of the battery, and the open end of the black wire to the negative side of the battery.

Step 3: Connect alligator clips to the motor

Connect the alligator clip of the red wire to the red lead of the motor, and the alligator clip of the black wire to the black lead of the motor.

Step 4: Measure the Voltage

Use a multimeter in voltage mode to measure the voltage across the motor. Use the module below if you need a refresher.

(Optional) Module: Measure the Voltage

Use a multimeter in voltage mode to measure the voltage across the motor. Use the module below if you need a refresher.

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
Step 5: Disconnect battery

Disconnect an alligator clip so that you do not use up the battery.

Explanation

The battery sends electricity through the circuit to power the motor. Motors use up lots of energy, so you may notice that over a short amount of time, the motor will spin slower until there is not enough voltage to move the motor.

Try It: Stall the motor

What happens if you hold the spinning end?
Reconnect the alligator clip, and use your fingers to hold the spinning brass end of the motor.
What happens?
  1. You should be able to stop the motor from spinning. This is called stalling the motor.

What do you think would happen if you were to use this amount of voltage on motors to try to move a robot?

+ Show Hint(s)
  1. The robot wouldn’t be able to move because there isn’t enough motor strength to move the robot! We need more voltage!
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