Wiring Fundamentals: Resistance
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Resistance
02.34
| 00:00 | - Resistance is a measure of how hard it is for the electrons to flow in response to an applied electrical pressure. |
| 00:06 | It can be thought of as a restriction the tap imposes on the flow of water when it's only partially open. |
| 00:13 | If we just barely crack the tap open and get a trickle of water coming out, this is a low flow rate as the tap is imposing a high resistance. |
| 00:20 | Alternatively if we open the tap fully, it will allow the maximum flow rate the main system can supply. |
| 00:26 | This is a high flow rate as the tap is now imposing a low resistance. |
| 00:30 | Back in the electrical world, the same concept applies. |
| 00:33 | We have discussed connecting one end of the wire to the positive terminal of a 12 volt battery and the other end to the negative terminal. |
| 00:39 | You should never actually do this however as the wire is like a pipe with the tap fully open. |
| 00:45 | It has a very low resistance to flow, so a very large and dangerous current will flow. |
| 00:51 | If we put something in the middle of the wire that the electrons find it harder to flow through, like a fuel injector for example, the resistance the fuel injector imposes, will decrease the current flow. |
| 01:01 | The key concept to grasp here is that different resistances cause different levels of current to flow in response to the same applied electrical pressure. |
| 01:10 | In our plumbing analogy, the mains pressure never varied from 60 psi but the flow of water varied in response to how far we opened the tap. |
| 01:19 | This is why most electrical devices in a vehicle have a pretty narrow range of voltages that they operate at. |
| 01:24 | They're designed with a specific resistance that allows the right amount of current to flow through the device for it to operate correctly. |
| 01:30 | This can only be done if the designer knows the narrow voltage range that the device will operate at. |
| 01:36 | Luckily for our industry we know this is typically between 11 and 14.2 volts. |
| 01:42 | If we apply a voltage that is either too low or too high, the wrong amount of current will flow and the device will either not work as expected or worse, be permanently damaged. |
| 01:51 | Another idea I'd like to touch upon when talking about resistance is the term load. |
| 01:56 | Electrical devices in the car are often referred to as placing a load on the electrical system. |
| 02:01 | This term describes how hard the electrical system has to work to supply the required current to the device. |
| 02:07 | As a device with a higher resistance will require only a small current, it's actually only placing a small load on the electrical system of the vehicle. |
| 02:15 | So load can be thought of as the opposite of resistance. |
| 02:19 | The lower the resistance, the more current flows, and the greater the load. |
| 02:23 | When you are reading or writing documentation, resistance has a unit of ohms, and a symbol of either a capital R, or a capital greek omega. |
