Rick,
I for one find it educational. I don't understand much at all about car
wiring or any wiring for that matter. Keep the tutorials coming.
Thanks,
Randy Widman
79 Red B
----- Original Message -----
From: "Rick Lindsay" <rolindsay@stoolhead.com>
To: "mgs" <mgs@autox.team.net>
Sent: Monday, December 22, 2003 1:45 PM
Subject: Electricity 101
> Hello Folks,
> It's a little quiet here at work today
> and I though I would use my lunch-hour to
> write a little tutoral on electrical circuits
> and wiring. A first installment is given
> below. So here goes...
>
> The electrical systems in our LBC operate on
> direct current or DC. That means that
> current flows in one direction only, unlike
> our household power. Another way to think of
> that is the electrons flow in one direction
> only.
>
> We're going to need to define a few terms
> here and that can be perhaps done best by
> including analogys.
>
> Voltage - Voltage can be thought of as the
> PRESSURE in the electrical circuit. This is
> a good time to remember that the water in a
> hose doesn't go anywhere if the flow is off,
> regardless of the pressure.
>
> Current - This relates to the VOLUME or
> AMOUNT of current that is or CAN flow in a
> circuit. One might think of this as related
> to the diameter of the water hose.
>
> Resistance - As the word implies, this is
> the impedance to electrical flow. Think of
> the knob on the water faucet (feeding the
> water hose) as adjusting the resistance to
> flow. Cut it off, infinate resistance, and
> no current flows. Open it full, zero
> resistance, and in theory, ALL of the water
> (or current) will flow!!!
>
> The parameters merge by the simple
> relationship, E = IR
> Of course, the engineers couldn't make it
> easy so here's what that means: E is
> electromotive force or VOLTAGE. I is
> current and R is resistance. The units
> needed to balance the equations are E in
> volts, I in Amps and R is Ohms.
>
> There is another pair of relationships that
> can help. They are P=IE and P=(ExE)/R. P
> is power in watts. The other terms are
> explained above.
>
> A quick example,
>
> If a car's headlight lamp is rated at
> 55watts then given a few other knowns, we
> can solve the puzzle.
>
> P=IE is rewritten with the unknown on the
> left as, I=P/E or as stated in words, the
> current in amps is the quotent of power in
> watts divided by voltage in volts. In our
> example,
>
> I = P / E
> I = 55 / 12
> I = 4.58 amps
>
> The practical side of this is that one 55
> watt headlight bulb draws about four and a
> half amps of current at 12 volts. That is
> like saying, to make a headlight bulb
> produce light, a pressure of 12 volts moves
> 4.6 amps of volume through the (hot)
> resistance of the bulb's filament. So what
> is the (hot) resistance?
>
> E = IR is rearranged to,
>
> R = E / I
> R = 12 / 4.58
> R = 2.62 ohms
>
> For completeness and to show that it works,
> please remember that P=(ExE)/R. If we put
> that back together as such,
>
> P = (E x E) / R
> P = (12 x 12) / 2.62
> P = 54.96 watts (which is as close to 55
> watts as one ever needs to get!)
>
> So it all works.
>
> Above I put (hot) in parenthesis because
> the resistance of a lamp's filament changes
> with temperature. As the temperature goes
> up, so does the resistance. That is
> exactly backwards from the way a
> temperature sensor works for an electric
> oil or coolent temperature gauge. The
> substance in the sensor has an inverse
> resistance profile. The resistance goes
> DOWN as the sensor heats up. That's a
> topic best left for another day.
>
> We also need to discuss fuses versus the
> current expected in the circuit and as
> related to the gauge and length of the
> wire in the harness. We can do that
> later as well but the short story is that
> the fuse used on a circuit must be large
> enough to carry the component's load (and
> the sometimes much larger impulse load
> experienced when a circuit is first
> energized) but not be so large that the
> wire will "fuse" or melt before the fuse
> fuses! There are lots of guidelines for
> wire gauge and length (resistance increases
> with length) but I can't put my hands on
> them right now.
>
> We can also talk about diodes later too.
> They are devices that allow current to flow
> through them in one direction only. More
> next time if you find this of any value.
>
> Happy Holidays!
>
> Rick
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