Wiring Fundamentals: Voltage
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Voltage
02.31
| 00:00 | - When we're dealing with electricity, it can be hard to develop an intuitive feeling about what is actually going on, and how the different concepts relate to one another. |
| 00:08 | After all we can't actually see electricity and we usually only feel it when something has gone very wrong. |
| 00:14 | To help us develop a sense of what is happening, we're going to use a household plumbing analogy. |
| 00:19 | We'll think about a simple water pipe with one end connected to the main supply pressure and a tap on the other. |
| 00:25 | This is something easy to visualise so we're all familiar with. |
| 00:28 | And for the purpose of automotive electrics, does a pretty good job of relating the basic principles to one another. |
| 00:35 | Voltage is equivalent to the water pressure applied to one end of the pipe by the water mains system. |
| 00:40 | If you live somewhere with decent water pressure, this might be 60 psi for example. |
| 00:45 | When you open the tap at the other end of the pipe all the way, you drop the pressure at this end of the pipe to the same as atmosphere. |
| 00:51 | As we now have 60 psi of pressure at one end of our pipe, and zero psi at the other end, there is a pressure difference of 60 psi across the length of the pipe and the water will flow along it out of the tap. |
| 01:04 | Heading back to the electrical word, this is like connecting one end of our wire to the positive terminal of a 12 volt car battery. |
| 01:10 | You're applying 12 volts of electrical pressure to one end of the wire. |
| 01:14 | If you then connect the other end of the wire to the negative terminal of the battery, it's like opening the tap. |
| 01:19 | You're applying zero volts of electrical pressure to the other end of the wire. |
| 01:24 | This means there's now a 12 volt difference in electrical pressure along the length of the wire and the electrons in the wire will start flowing. |
| 01:31 | This might seem pretty simple to follow initially, but there are some subtle points that require a little more explanation. |
| 01:36 | In our pipe analogy you can imagine that when you had your tap at the end of the pipe closed, you could fit a pressure gauge to the pipe anywhere along its length and you will measure the 60 psi of pressure being applied by the mains system. |
| 01:49 | This is because the water is not flowing. |
| 01:51 | It has nowhere to go because the tap is closed. |
| 01:54 | Similar to this, in the electrical world, when you connect one end of a wire to the positive terminal of a battery but leave the other end unconnected or floating, it's like the tap is closed. |
| 02:04 | The electrons have nowhere to go, so they won't be flowing, and you'll measure the 12 volts of applied electrical pressure at any point along the wire. |
| 02:13 | The key concept here is that flow, be it physical or electrical, only happens when there is a difference in pressure at either end of the pipe or wire. |
| 02:22 | When you're reading or writing documentation, voltage has a unit of volts, and the symbol of a capital v. |
