+1 on all of that!
On electrical matters, I will always defer to RG and 2M - but just reinforce: the only way to measure current (unless you're using an inductive meter which "clamps" on the wire) is to
disconnect the circuit and
put your meter into it in series with all of the other loads. Measuring between two points in an active circuit will not give you a usable measurement of the current in the circuit.
My late Dad - who was a "
toaster" himself - always cautioned me that current measurement is a fair step-up in complication from voltage and resistance (or continuity) measurement. As RG says, you must have some sort of idea of how much current (how many amperes or amps) you expect so that you can set your meter to the proper level. Dad explained it to me (
a mere mechanical engineer - or "plumber" as he liked to call me) in this way:
- voltage is like water pressure - you can just stick a gauge into a pipe (which is like a wire) or into a water tank (i.e. a battery) and measure the pressure whether water is flowing or not. When the water flows, the pressure will drop (just like the voltage does when you start a bike);
- electrical current is like the flow of water in a pipe and the only way to measure it is to open the pipe and have a look at what is going through it.
Resistance is the relationship between voltage and current and it is called Ohms Law after
Georg Simon Ohm who was a German physicist in the 18-19th century. Ohm published his work in 1827 as a theoretical scientific treatise - and by golly, he was right on! Old Georg (no "e" on the end in Germany - its pronounced "
gay-org") was a pretty sharp fellow (
here's a photo from Wikipedia - he doesn't look like a very fun guy to me...but he does have a snazzy medal from the Kaiser around his neck):
Ohm's Law states the following in a handy graphical format (
much of which is also swiped from Wikipedia):
Ohm's law triangle
Ohms law wheel with international unit symbols
The interchangeability of the equation may be represented by a triangle, where V (
voltage) is placed on the top section, the I (
current) is placed to the left section, and the R (
resistance) is placed to the right. The line that divides the left and right sections indicate multiplication, and the divider between the top and bottom sections indicates division (hence the division bar). In
circuit analysis, three equivalent expressions of Ohm's law are used interchangeably:
Where V = voltage, I = current and R = resistance. My Dad always used the symbol "E" for voltage and I noted that RG did the same thing the other day. I guess it is a
toaster/EE" thingy but to me, it didn't make a lot of sense because voltage starts with a "V". I think they called "
electromotive force" for a while and that is where the "
E" came from.
I can add (
and this does not exactly work for AC circuits..) that electrical
power, which is measured in watts (after James Watt - a Scottish engineer who was one of the developers of the steam engine) is equal to VI or the multiplication of voltage times current. So, if you want to run a 50 Watt headlight, at 12 volts, it will take 50 / 12 = a little bit more than 4 amps of current. This means that the 200 watt alternator in our XS650 bikes can put out about 200 / 12 = 16.6 amps at full power.
That is why you cannot run a huge bank of fog lights on our bikes - without depleting the battery. They simply take too many amps of current.
Just one more thing: if you do all the math, a
horsepower (which is a unit of mechanical work in the British measurement system) is equal to
746 watts and that is why you often see the HP of bikes in Europe written as
xxx kW - or
kilowatts. A
kilowatt is 1000 watts or about 1.3 HP (just like a
kilogram is 1000 grams and a
kilometer is a 1000 meters).
So, a 45 HP Yamaha XS650 engine can produce 45 x 746 = 33,570 watts or 33.57 kW. of power. Thus, the
200 watt XS650 alternator when working at full power only consumes about: 200 / 33570 = 0.00595 or about 0.6% of the power being produced by the engine.
Some months ago somebody suggested that shutting their lights off or using LEDs would make the bike go faster because it would decrease the amount of power required to run the alternator. I guess
in principle, there
is an effect, but frankly, you would make your bike go even faster if you simply skipped that up-size on the fries and Coke at McDonald's a few times new month, because the alternator only consumes about
half of one percent of the engine power being produced. The real reason to use LEDs is that they are much more reliable than incandescent bulbs.
OK - I think that I've made your eyes bleed enough for now. Let's all crack open a frosty BEvERage and relax!
Pete
