| | 103 | [[Image(http://cdn3.volusion.com/vyfsn.knvgw/v/vspfiles/photos/am-0282-2.jpg?1500469210,20%,left,nolink)]] [[Image(http://www.mouser.com/images/littelfuse/lrg/cartridge-3ag_sb_final_1_213_218-228.jpg,20%,left,nolink)]] |
| | 104 | Fuses and circuit breakers are devices designed to protect against overheating caused by over-current conditions (more current than the circuit/wiring is designed to handle). Fuses are just thin pieces of wire (usually encased in glass or plastic) that you include in your circuit to protect the rest of the circuit. If too much current flows through the circuit, the fuse wire melts and opens (disconnects) the circuit). The fuse wire fails safely inside its housing at a known current level to prevent catastrophic failures (melting insulation, fires, etc.) in the rest of the circuit. |
| | 105 | |
| | 106 | A circuit breaker is often called a resettable fuse; it is an electro-mechanical device that is also designed to be included in a circuit and open if too much current flows through it. Breakers usually are spring-loaded and use two dissimilar metals that deform differently as they get hotter (due to current passing through them). If they deform enough, they snap apart and open the circuit. |
| | 107 | |
| | 108 | FRC robots include a master [http://www.andymark.com/120-amp-robot-main-circuit-breaker-p/am-0282.htm 120A circuit breaker] that connects/disconnects the battery from the rest of the robot. This breaker includes a button to manually trip the breaker and is often used as the on/off switch for the robot. Each major circuit (e.g. motor) in the robot has its own additional fuse or breaker appropriate for the wiring and amount of current the circuit should carry. For example, motor circuits are often protected with a [http://www.andymark.com/40-Amp-Snap-Action-Breaker-p/am-0288.htm 40A snap breaker] that opens when it heats up with more than 40A of current and closes when it cools down again. This helps prevent motors and motor wires from burning up if the motor stalls but remains powered. |
| | 109 | |
| | 110 | * Exercise: blow a fuse |
| | 111 | * Materials needed: battery, alligator jumper wires, 5x20mm glass fuse |
| | 112 | * Activity: |
| | 113 | * Observe the fuse wire through the glass |
| | 114 | * Connect the battery to either end of the fuse (short circuit) using the jumper wires |
| | 115 | * Observe the blown fuse through the glass |
| | 116 | * What happened: the battery supplied a large amount of current through the fuse which caused the fuse wire to heat and melt, opening the circuit |
| | 117 | |
| | 118 | * Exercise: try a breaker |
| | 119 | * Materials needed: Robot with battery connected (peanut or competition robot) |
| | 120 | * Activity: |
| | 121 | * Use the 120A master breaker to turn power on and off to a robot |
