Thursday, July 1, 2010

Electricity Unmystified

Now that you’ve removed most of your car’s electrical system, it may be a good time to learn what electricity is. You don’t need to be a Thomas Edison, Nikola Tesla, or Andre Ampere (yes, that’s a real person) to pick up the basics. You just need a willingness to learn and a few minutes to read. So, if you’re game, read on…

I’m sure you’ve heard analogies to the movement of water when referring to how electricity works where voltage and current are compared to pressure and flow. Not that these methods don’t have their own merit, but I think it might be a little abstract for this forum. Although the physics of motion, gravity, fluid mechanics, and electricity all have underlying similarities, this lesson will remain relevant to your car’s electrical system and will speak to the storage and flow of electrons. But, what’s an electron?

An electron is a sub-atomic particle with a negative electrical charge (-). As you know, similar electrical charges and similar magnetic forces repel each other, so these electrons want to be as far away from each other as possible. Now here’s the catch: The electrons in non-conductive materials, say wood, do not have the freedom to move around as much as they do in materials that are conductive, like copper. It’s the atomic and molecular makeup of the matter that’s the matter. Conductive materials just have a composition that’s favorable to an electron’s freedom of movement. Taking this all in: A toothpick has a bunch of electrons in it that hate each other, but they can’t move around. A copper wire, on the other hand, has a bunch of electrons that hate each other, but they’re free to wander about. The copper has more of cloud of electrons while the wood has more of a structure of the little critters. How does that help? Since these electrons are free to move about, they can travel through conductive materials en masse. And, since they carry an electric charge, their movement creates detectable and useable forces and energies.

A little more about their charge: If these electrons were electrically neutral (without a charge), they would not repel each other and would just hang around in whatever shallows were available. If they were attracted to each other, they’d clump up somewhere and probably get stuck within the fabric of whatever matter they inhabited. But, since their charge keeps them at a distance from one another, in a conductive material they spread out as much as they can to fill every crevice and crevasse within, say, a copper wire – but no further. The electrons will be ‘bound’ to the wire until anything conductive comes into contact with it: air, wire sheathing, electrical tape are all non-conductive so it stands to reason that these repulsive electrons can only go as far as the conductive material will allow. Why is this important? The electron ‘cloud’ can build up pressure as more and more electrons are forced into the same spaces. This pressure is referred to as potential or Voltage (our first electronic buzzword).

Take a deep breath, reread what you’ve just read, and maybe read it again until you’re confident with my explanation of electrons. When you’re ready, read on.

Voltage is the measure of the relative difference in the amount of electrons in one area compared to another. In your car’s battery, if charged fully, there is an unimaginable number of electrons hanging out on the negative (-) side and a depletion of them on the positive (+) side; the difference is measured at an average of 12 Volts (12V). Your car’s electrical system provides a conductive path for the electrons to travel from the negative battery terminal (anode) to the positive battery terminal (cathode). And in that path are all sorts of things that utilize the different properties of the storage and flow of them ‘lectrons. Lights, starters, horns, radios, spark plugs, alternators/generators all use different characteristics of electrons and we’ll get into these properties next.

So, now you know that electrons are stored in your battery, that they move in conductive materials, that the car’s wiring provides a conductive path for them, and that when there’s a lot of them located in one area, a voltage can be measured. Now, what can these electrons do? Well, here are some properties that we’ll get into:

Electrons flow at different rates through different materials.
Electrons cause heat due to molecular friction when they traverse materials.
Electrons create magnetic forces when they move.
Electrons repel each other and are susceptible to magnetic forces.

It’s pretty neat that all things electrical work because of these properties – TV’s, cell phones, electric toothbrushes, the game of Operation. Now, let’s tackle the first property: Electrons flow at different rates through different materials. You already know that electrons are free to move about in conductive materials – metal is the ubiquitous conductor – and they don’t move so freely in non-conductive materials like air or plastic. Our first two uses of this property: Wires and Switches. Wires provide the path for electrons to travel and switches control that path. When a switch is ‘off’, there’s an airgap between the two wires; when ‘on’, the wires can conduct. Pretty simple stuff. We’re just talking flow / no-flow right now, but I said different rates before. WTF does that mean? I lied about non-conductors - the truth is that electrons will flow through a lot of different materials, just at different rates. Glass, wood, air, plastic are at one end of the scale and copper, aluminum, and gold are at the other. This leads to the opposite of conductance: Resistance. Resistance is measured in Ohms (Ω) and this is what regulates how much flow goes through what. The resistance of air is somewhere around 400,000,000,000,000 Ω/meter and the resistance of copper is 0.00000002 Ω/meter. So, for all intents and purposes, non-conductors have very high resistance and conductors have very low resistance – high and low enough to be negligible in calculations. Now what? Voltage, as defined earlier, is the storage of electrons; these Ohms are a measure of how much resistance the electrons encounter on their journey through stuff – we need to call the flow something: Current. Current is measured in Amps (A) and can be found through math: Voltage is Current multiplied by Resistance. If you want to know current, you need to rearrange it a bit and divide Voltage by Resistance. Math scares people, so we’re not going to be a-caculatin’ too much – just enough to do more ‘splaining.

Let’s say you have a headlamp that’s 4Ω. In your car’s 12V system, the current would then be 12V / 4Ω, which equals 3A. This provides a great lead-in to Fuses. Fuses are there to protect your wires. Since these electrons are flowing through the copper at extraordinary speeds (close to the speed of light), the more that flow, the more they bump into things and the more heat they create as they’re traversing the wire. If this heat reaches a high enough temperature, guess what? Copper melts. And as the copper melts it could cause a fire or it will just melt the plastic sheathing of it and the surrounding wires, causing a very, very unpleasant situation. At a minimum, it will cause a break in a wire somewhere - now think about all of the wires that you just pulled from your car and then think about how difficult it would be to figure out if there was a break in any one of those wires all bundled up in the harness, under your carpet, in your trunk, wherever. Wouldn’t it be easier to have a specific location that you could almost guarantee would be the weak link in this electric chain? Your fusebox is that weak link. All wires are rated at a maximum amperage that they can safely handle. Let’s say that your headlamp wire can safely accommodate 5A. In our example above, we see that only 3A will be going through the wire, so we’re at a safe level. Now, let’s say that you want to install a fog light and you decide to tap into this headlamp wire. Let’s also say that it’s a 4Ω light too and will, therefore, draw another 3A. Now, you’ve got 6A traveling through a wire that’s made for 5A of current – something’s going to give. Fuses are just like wires in that they’re rated for the maximum allowable current. The difference being that they are made to localize the break/melting in an over-current situation. As long as the fuse is rated at less than the wires, any break will be at the easily-findable and easily-replaceable fuse. So you have some wire, a headlamp, and, say, a 4A fuse all working together just fine and happily with 3A of current coursing through the circuit. Now, we connect that fog light and, all of a sudden, the current jumps to 6A, the fuse melts, and all is dark. That fuse sacrificed its happiness to protect the wires and save you a crap-load of troubleshooting and, probably, swearing. Thank you, fuse.

Getting into the more exciting electrical components of your car, we’ll talk about lights and then step up the game a bit to learn about ignition systems, motors, relays, and whatnot.

Lights: As described earlier, wires heat up when a lot of electrons flow. The heating properties, when properly harnessed, offer a great deal of benefits to humans such as stoves, ovens, household heating, and…Lights. It just so happens that degrees of heat are detectable just like colors are to our eyes. Just out of reach of our visible spectrum is infrared – this is where warm and hot (but not too hot) is ‘visible’ with specialized equipment. As things heat up a bit, the temperature creates higher and higher frequencies and the heat starts to enter into our field of visible frequencies and is seen as red then orange then blue then white. The lights in your car make use of this property and special metal is used as the wire in the light bulb: Tungsten. Tungsten is a metal with a very, very high melting point – high enough to withstand the heat of white-hot situations. So, your lights are just wires that can withstand the heat without melting (although, they eventually do fail).

Blinker Switch: Another device that uses heating to its advantage is your blinker switch (or flasher) that regulates the momentary on-and-off of your turn signals. Inside the flasher is something called a bi-metallic strip. This bi-metallic object is just what you’d think it is: a strip made from two metals. Big deal, huh? The magic lies in the properties of these two metals. I stated earlier that different materials have different resistance due to the molecular makeup impeding the flow of electrons. Well, that’s just one measurable property of matter. Another is what’s called heat expansion. You know that when things get hot, they expand – you may not know that different materials expand at different rates. So, if you take two dissimilar metals with different expansion rates and glue them together, the ‘bi-metallic strip’ will have one side that expands faster than the other side and the strip will bend when heat is applied. That’s exactly what’s going on in your blinkin’ system. You hit your turn indicator, power goes to your blinker switch: your turn signal is on. (Slow motion time.) As the current heats up the bi-metallic strip, it starts to bend and keeps bending until it bends enough to cause a break in the circuit. Current stops, turn signal is off. Since there’s no more current, there’s no more heat being generated and the strip begins to cool down and starts to bend back to its original shape until contact is made again and the current starts and your turn signal is on again. Re-peat, re-peat, re-peat, re-peat…

Spark Plugs: Your spark plugs make use of heat, but in a slightly different way. One thing I neglected to tell y’all is that non-conductors (things with high resistance) are prone to ‘dielectric breakdown’ where once a threshold of voltage is met, the material can’t take it anymore and lets it all flow. The most dramatic example is, of course, lightning. Lightning is happening on a much smaller scale all the time in your motor. Enter the spark plug. Spark plugs operate at about 30,000 – 50,000 volts and they basically supply a gap for the spark (current) to flow. The air/gas mixture within that gap is the non-conductor in this case and when that spark jumps, it heats up quick and hot - enough to ignite the surrounding air/fuel mixture and start a chain reaction that causes detonation and makes your motor run. Sounds good, but 50,000 volts? Where does that come from? Read on…

Ignition Coil: Supplying the required high voltage for your spark plugs is the ignition coil. This little device turns your car’s 12 volts into a vigorous 30,000 to 50,000 volts. Exploiting the 3rd and 4th properties of electrons, the coil is able to use electric and magnetic forces to multiply voltage on a nearby, separate circuit. Holy crap. Let me explain. If you took a piece of straight wire and put a current through it, a magnetic field is created. Much like all invisible forces, the magnetic field is mysterious in nature, but we do know that it circles the wire around and around and gets stronger as more current flows. It also works the other way around: if you could somehow create a circling magnetic field around a straight wire, you’ll create a flow of electrons proportional to the field. Bigger field = bigger current. Now get this: if you have two wires next to each other and apply a current to one, the resulting magnetic field will create a proportionate current in the other. Now, here’s the fun part: the magnetic fields are additive, meaning that if you have two wires carrying current, now you have twice the field. So, if I take that straight wire and loop it around and around into a coil, I increase the magnetic field over and over again with each loop. Conversely, if I loop a coil around a magnetic field, the more of it I will ‘capture’ and the more of that force I can harness and use. Also, if you stick an iron rod (or any conductor) inside the loops, the magnetic fields are ‘focused’ through it to help reach the field’s full potential. So, if you have 2 coils wrapped around the same axis (an iron shaft), one coil will impart a current on the other one. AND, if the primary coil (the one connected to your 12V system) has, let’s say 1000 times as many loops in it than the secondary coil (the one connected to your spark plugs), the resulting voltage will be a thousand-fold, or 12,000 volts. Sounds great, but there’s one drawback: Current only flows when there’s a change in the magnetic force, so a constant magnetic force will not really create a current, but a force that goes from zero to whatever or from whatever to zero will. It’s the ‘whatever to zero’ that packs the punch in your car. The distributor controls which spark plug gets the juice and also controls the voltage going to the primary coil. When the coil is charged with a steady 12V, everything is dandy, but when that 12V is suddenly taken away, the magnetic field collapses and BLAMMO, that high voltage is sent to the spark plug on a mission to explode gasoline.

Relays: Relays are magnetically-controlled switches typically used for controlling high-current devices without sending a bunch of current through your entire wiring harness or the controlling switch. Think about your starter: without a relay in the mix, that huge battery cable would need to come through the firewall, into your ignition switch, back through the firewall, and to the starter. A relay can be located closer to the source and can be controlled remotely with smaller, less expensive wires and switches. They’re not as mystical or exciting as the coil, but they operate in a similar way - I gave you a hint earlier in that they are ‘magnetically-controlled’. The magnetic portion of the switch is basically the coil’s kid brother. If you picture the iron rod with 2 coils looped around it from the previous pontification, take the secondary coil out of the equation and you’re left with a boring electromagnet. The more current and/or loops you have surrounding the core, the more magnetic force you’ll have. Unlike the imposed current on the secondary coil, the electromagnet will continue to produce regardless of changes in the primary current – the magnetic fields will just change proportionately. So now we have the magnet that can be turned on and off – how does that control a circuit? Contacts. This magnetic, coily device controls a spring-loaded metal plate that either makes or breaks a circuit. The plate is positioned on a pivot at a short distance from one end of the iron rod (magnet) and when enough of a magnetic field is created to overcome the spring pressure, the plate is compelled to stick to the magnet and contacts complete the connection, allowing current to flow in a separate circuit. Whoa – I think I just bored myself. On to more exciting components…

Motors/Starters/Generators: We know that if you coil a wire around an iron core, you can impart a controllable magnetic field. We also know that you can recoup current from that magnetic force by looping another coil around the same rod. But what if I had a traditional, everyday magnet? That everyday magnet produces a constant, non-controllable magnetic field with a certain polarity. You’ve played with enough magnets to know that they stick together or they push each other away. That’s what electric motors run on: Polarity. Insert new concept here: Electromagnets have polarity, too. So, if I have an electromagnet (like the one described in the Relay bit) and a permanent magnet, they too will attract or repel each other depending on which sides you put together. Another advantage to the electromagnet is that if I switch the wires on the battery, I switch the direction of current and, consequently, I switch the polarity. So now the electromagnet will attract the other side of that permanent magnet and versa vice. So now that you can control polarity, we can build upon your newly-gained knowledge and conceptualize something useful. If I were to mount a permanent magnet like a pinwheel and hold it near an electromagnet, it would be free to spin until I turned the electromagnet on – then it would move and arrange itself accordingly, based on polarity. Now, if I reverse the polarity, that magnet will flip and do a 180, aligning itself with the revised polarity. If I keep reversing the polarity back and forth, with the right timing, I can get that magnet-on-a-stick humming pretty good. Alas! The electric motor. The difference between our magnet pinwheel and, say, your starter motor, is that there are more (and stronger) electromagnets surrounding a stronger permanent magnet, making a smoother and more-powerful spin. The timing for reversing polarity is also based on the position of the axis, so the faster it spins, the faster the poles are being reversed. Make sense? Good. If you haven’t already guessed, a lot of things electrical are reversible, especially when you throw magnetism into the fray. This holds true for motors and generators alike in that electricity makes motors move much in the same way that movement makes generators create electricity. Whaaat? Remember the secondary on your coil? It turns magnetic forces into current, right? Well, what if you got rid of the primary and stuck a magnet on the end of that iron bar? It would magnetize the core of your coil and supply the same magnetic forces as the primary did. Also remember that the secondary will not receive its fix of current unless the magnetism is changing. Oh crap: how do you change the magnetic force from a permanent magnet? The answer, my friend, is to move the magnet. Since magnetic forces weaken as they stray from the source, the further away this permanent magnet is, the less magnetic forces the core will witness and the more it will feel as the magnet gets closer. So moving the permanent magnet closer to and further from the coil will change the magnetic field and will create that ever-so-desired electric current in the secondary. Taking our pinwheel example and rearranging it a bit, let’s spin the pinwheel. As the magnet gets closer, the coil is getting more and more magnetism and a current is realized in the coil. The one end of the magnet comes and goes and the other end starts getting closer. Because it’s the other end of the magnet, its polarity is reversed and the current flows in the other direction. Much like the motor example, the wires need to be reversed somehow to get the electrons coming out the right wire as the polarity swaps back and forth. Expanding upon this, it’s not a hard task to imagine power being generated from a rotating magnet. There are some differences between a motor and a generator, primarily to prevent your generator from running like a motor when the battery is connected.

Distributor: We touched upon the distributor earlier, but I felt it would have broken up the fun we were having in our adventure from lights to motors. The distributor is actually more of a mechanical switch than some fancy electrical component (I'm talking older ones here). Strictly speaking, the thing distributes high voltage to each spark plug just at the right time for proper combustion. Secondarily, it provides the contacts/switching for the coil to perform its encore performance over and over and over again. I don’t want to lessen the importance of the distributor, but I don’t see the point in expounding upon a sophisticated switch during this blog session. Too bad, distributor – you’ve been knocked down a few pegs.

I hope this has proven to be useful and inspiring in your search for understanding all things electrical. Now here’s a bonus question: If electricity is the flow of electrons, why the heck is it the positive (+) pole on the battery that powers everything in my car?

The answer involves some perspective. Since we’re only dealing with metallic conductors, we’re only looking at a small subset of materials in whole. Just as I explained about how the electrons are free to move about in metallic conductors, there are many other types of materials (semiconductors) that hold electrons and allow the flow of protons. Protons? Protons are electrons’ positively-charged counterparts (yay, team!). They act the same, except they have an equal, but opposite charge. So, given that electricity, in reality, is the flow of either electrons or protons, it stands to reason that current can flow in either direction. With the importance of semiconductors increasing throughout the years, it was necessary to come up with a convention to define current flow. As I said, metallic conductors are a small portion of material science and, consequently, represent a minority of how electricity actually flows. Majority ruled and the convention of electric flow was standardized to go from (+) to (-) and we’re left with a somewhat puzzling situation.

Understand? Great! We’ll get back to the restoration next time…