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

Fuses

Mini Project Motor Box with Fuse

High current levels in circuits can be dangerous, and also can damage components in a circuit. There are times where component replacement can be very costly.

To prevent damage to components from high voltage or current, a device called a Fuse can be added inline with circuits. A fuse typically is a metal wire or strip that melts when too much current is flowing through the circuit.

In this project, we will add a fuse to the Motor Box circuit.

Motor Strength: Required items and tools

Find the following components in your kit:

  • Fuse and Fuse holder with Leads Fuse and Fuse holder with Leads
  • Wire cutter and wire stripper Wire cutter and wire stripper
  • Electrical Tape Electrical Tape
  • Two Coin Cell Batteries Two Coin Cell Batteries
  • The Motor Circuit from the previous lesson The Motor Circuit from the previous lesson
  • Digital Multimeter Digital Multimeter
  • Alligator Clip Alligator Clip
  • Wire Wire
  • Alligator Clip Crimper Alligator Clip Crimper
  • Wire Stripper Wire Stripper
Step 1: Add a Fuse

Modify the Motor Box to add in the Fuse. Begin by cutting and stripping the Fuse holder wire toward the center of the loop, and attaching an alligator clip to one end of it. Also create a black wire with one stripped end and one end with an alligator clip.

(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: Test Continuity

Test the continuity of the fuse with multimeter to see that it lets electricity through. Feel free to also check the black wire you made.

(Optional) Module: Testing Continuity

Follow along with this module to refresh your memory on how to test continuity.

Testing Wires with a Multimeter: Required items and tools

To begin testing wires, you will need the following:

  • Digital Multimeter Digital Multimeter
Checking Continuity

A multimeter can be used to test for an unbroken electrical connection between two points. Something with no breaks is called "continuous", so this process is called "continuity" testing.

Selecting Continuity Testing Function

The continuity testing function of the multimeter tests for electrical continuity between two points that you touch the multimeter's leads to.

Tip: If there is a continuous connection, the multimeter will make a beep sound, so the icon for this mode usually looks like a "sound waves" symbol.

  • Some multimeters do not include this feature. If yours does not, follow the steps below but use the lowest-value Resistance test feature (Ω) on your multimeter instead, and instead of a beep, look for a resistance value of zero or near zero to be shown on the screen.
Safety Notice

The continuity tester does not work on circuits that have power running through them. Disconnect power from the portion of the circuit you are testing and test the parts individually. The multimeter may be damaged if you attempt to use this feature on a powered circuit.

Step 1: Plug black lead into multimeter

Plug the black lead of the multimeter into the COM terminal.

Step 2: Plug red lead into multimeter

Plug the red lead of the multimeter into the terminal with one of the following icons next to it:

  • Continuity Symbol Continuity Symbol
  • Ohms Symbol Resistance (Ohms) Symbol
  • Voltage (Volts) Symbol Voltage (Volts) Symbol
  • Diodes Symbol Diodes Symbol

Tip: The continuity test feature is electrically similar to several other multimeter functions, so it usually shares a plug and a spot on the dial with one of them. Different multimeters have it share with different modes.

Step 3: Turn dial to Continuity Testing setting

Turn the dial to the connectivity testing setting.

Some multimeters, like the orange one shown, have multiple functions on a dial setting. You may need to press the FUNC or function button to switch the multimeter to the connectivity testing setting. Look for the connectivity symbol on the screen of the multimeter.

Step 4: Touch leads together

Touch the metal parts of the multimeter leads together. The multimeter should make a sound while they are in contact (because the two leads are electrically connected to each other).

  • If no sound is played, check your connections and try again.
Step 5: Touch the leads to the wire

Touch the two leads to the ends of the wire you want to test. If you hear a sound, it means that there is a continuous electrical path between those two points.

  • This means there is no connection between the two points. Try to narrow down where the problem is by testing shorter portions of the wire. For instance, try touching the leads directly to the conductor in the wire -- if that part passes, then the problem must involve one of the connectors.
  • This either means you are trying to test for continuity across a component like an LED that cannot be tested using this mode (use Diode test mode instead), or it means the connection is loose.
  • The connector may be not be tightly crimped onto the wire conductor. Try tightening it.
  • You may also have damaged the conductor itself while attaching the connector -- for instance, you might have accidentally cut into the conductor while removing the wire insulation. This generally cannot be repaired, and you should remake that portion of the wire.
Step 3: Attach to Battery

Attach the postive side of battery to the stripped wire end of the Fuse holder lead. Connect the black wire to the negative side of the battery. Electrical tape works well for attaching to the battery.

Step 4: Attach to Motor

Complete the circuit by attaching the alligator clip of the Fuse holder lead to the motor lead.

Step 5: Measure Current

Measure the current (amperage) with the multimeter. What is it reading?

(Optional) Module: Measuring Current

Follow along with this module to refresh your memory on how to measure current.

Testing Wires with a Multimeter: Required items and tools

To begin testing wires, you will need the following:

  • Digital Multimeter Digital Multimeter
Checking Continuity

A multimeter can be used to test for an unbroken electrical connection between two points. Something with no breaks is called "continuous", so this process is called "continuity" testing.

Selecting Continuity Testing Function

The continuity testing function of the multimeter tests for electrical continuity between two points that you touch the multimeter's leads to.

Tip: If there is a continuous connection, the multimeter will make a beep sound, so the icon for this mode usually looks like a "sound waves" symbol.

  • Some multimeters do not include this feature. If yours does not, follow the steps below but use the lowest-value Resistance test feature (Ω) on your multimeter instead, and instead of a beep, look for a resistance value of zero or near zero to be shown on the screen.
Safety Notice

The continuity tester does not work on circuits that have power running through them. Disconnect power from the portion of the circuit you are testing and test the parts individually. The multimeter may be damaged if you attempt to use this feature on a powered circuit.

Step 1: Plug black lead into multimeter

Plug the black lead of the multimeter into the COM terminal.

Step 2: Plug red lead into multimeter

Plug the red lead of the multimeter into the terminal with one of the following icons next to it:

  • Continuity Symbol Continuity Symbol
  • Ohms Symbol Resistance (Ohms) Symbol
  • Voltage (Volts) Symbol Voltage (Volts) Symbol
  • Diodes Symbol Diodes Symbol

Tip: The continuity test feature is electrically similar to several other multimeter functions, so it usually shares a plug and a spot on the dial with one of them. Different multimeters have it share with different modes.

Step 3: Turn dial to Continuity Testing setting

Turn the dial to the connectivity testing setting.

Some multimeters, like the orange one shown, have multiple functions on a dial setting. You may need to press the FUNC or function button to switch the multimeter to the connectivity testing setting. Look for the connectivity symbol on the screen of the multimeter.

Step 4: Touch leads together

Touch the metal parts of the multimeter leads together. The multimeter should make a sound while they are in contact (because the two leads are electrically connected to each other).

  • If no sound is played, check your connections and try again.
Step 5: Touch the leads to the wire

Touch the two leads to the ends of the wire you want to test. If you hear a sound, it means that there is a continuous electrical path between those two points.

  • This means there is no connection between the two points. Try to narrow down where the problem is by testing shorter portions of the wire. For instance, try touching the leads directly to the conductor in the wire -- if that part passes, then the problem must involve one of the connectors.
  • This either means you are trying to test for continuity across a component like an LED that cannot be tested using this mode (use Diode test mode instead), or it means the connection is loose.
  • The connector may be not be tightly crimped onto the wire conductor. Try tightening it.
  • You may also have damaged the conductor itself while attaching the connector -- for instance, you might have accidentally cut into the conductor while removing the wire insulation. This generally cannot be repaired, and you should remake that portion of the wire.

Explanation

Fuses are often used to robotics to prevent damage to the components in the system. You may see devices that are similar to fuses called a Circuit Breaker.

Much like the metal-wire type fuses we learned about earlier, Circuit Breakers detect the voltage or current within the system and will open a mechanical switch that opens the circuit so that the circuit no longer has voltage. Electrical boxes in homes typically have these types to protect your home.

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