How can I learn about the laws etc and basics of metering? Do you have a good source for a beginner?
I'll see if I can find any, but maybe other members here can beat me to it. It is well explained with the analogy of an overhead waterreservoir (like an oldfashioned toilet) and it's pipe downwards. I know some pics, but they're in Dutch, so to speak
. Volt is the pressure, the water in the reservoir that wants to go down as soon there's an opening. Volt is named after Donald J. Volta, a good friend of mine, did a tremendous job, many may not know this, but he did a truly great job. There's a difference in potential simply because the reservoir is up there (
+) and where it wants to go to is down below (
-). In a DC system like in cars and motorcycles the
+ wants to go to
-. Actually the electrons travel the other way around but, hush, hush, we'll keep that a secret. Back to that oldstyle toilet with its overhead reservoir. When you pull the chain to flush it (think pressing a switch in a car) the water rushes down and it depends of the diameter of the flushpipe how much water per second will go down. The narrower the pipe, the more resistance, the longer it takes to empty the reservoir. The designer has estimated how much force is needed to flush away your delivery or (let's go outside where we have fresh air) make a waterwheel turn. So there is the difference in potential which we express in Volts, there is resistance which we express in Ohms (named after Donald J. Ohm who also happens to be a good friend of mine) and there's the current (the rate of electrons) which we express in ampères (amps). The power output of the waterwheel is Watts (named after Donald J. Watts). Did I already say Watts is a very good friend of mine? Watts, Ohm and Volt, three great guys that did an excellent job. Without them we wouldn't even have had the electric chair, can you imagine? Think of it!
Let's take a bike that has a headlamp that is rated 60 Watts and also has heated grips that are rated 120 Watts That's the way the lamp and the grips were designed. We could come back to that later eventually. If we apply Ohm's law in a 12V system like ours, it would mean that the 60 Watts lamp would draw 5 amps, because 60(Watts):12(Volts) results in 5(A). Ohms law. The 120 Watts grips will draw 120:12= 10 amps. Now take a truck that doesn't have 12V but a 24V system. A 60 Watts headlamp now will draw 60:24= 2,5 amps and the heated steering wheel, will draw 120:24= 5 amps. Why do we want to know amps? Well, when we know how many amps will flow, we can determine what size fuse we will need to guarantee that the flow of energy is interrupted immediately when an excess is demanded by an accidental shortcircuit. Why? Well first reason is ofcourse the battery would be depleted very quick, but also the wires, that are simply too thin to transport the all too sudden demand (flush of electrons), would burn. We will also be able to choose the right diameter wires (our flushpipes remember?). So a 24V equipped truck actually can do with thinner wires for the same consumers then our 12V bikes and in a vintage 6V T-Ford you would need thicker wires. Now we also mentioned Ohms. Ohms is how we measure resistance. Let's take this 60 Watts lamp that draws 5A. The purpose of the bulb is to give light and therefore the designer created a very thin wire inside (filament) that will glow when the circuit is switched. It's the resistance that makes it glow. Also resistance can be measured and it's done in Ohms.
If I apply Ohm's law and
if I tell you, the resistance of that lamp (its filament) will be 12V:5A= 2,4 Ω, you can now deduct yourself what Ohm's law is about. Simple, isn't it? Here you'll find a handy calculator:
http://www.rapidtables.com/calc/electric/ohms-law-calculator.htm Now scientists have agreed to rename Volt in 'U', amps in 'I' and Ohms in 'R'. Just to inform you if you google Ohm's law which I suggest you do. But we bikers can forget about U, I and R. To keep it simple,
you, for the time being, just remember that oldstyle toilet, your headlamp bulb and you'll be fine. As you play with this - and you
will - you'll develop your understanding more and more and, who knows, some day you may even make your own electric chair. But hey, don't let your kids sit on it, before you have tested it yourself, OK? A few things you should know using your multimeter. You measure Ohms only when the current is switched
off. Measuring amps ofcourse when switched
on. But I suggest for the time being you only measure Volts or Ohms. Most of us never measure amps. There's little or no need to.
First exercise for you would be to hold the red probe of your new meter against the + terminal of your battery and the black to the negative terminal. I bet you'll read between 11 and 13 Volts. Just don't try to read Ohms in this situation, because your meter is now part of a circuit that is
not off.
