Date:         Mon, 6 Aug 2007 10:45:40 -0700
Reply-To:     David Kao <dtkao0205@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Kao <dtkao0205@YAHOO.COM>
Subject:      Re: LVC: Learning Electricity & Testers
In-Reply-To:  <c4e7c5f90708061006x31bedca4t2a06576839050af8@mail.gmail.com>
Content-Type: text/plain; charset=iso-8859-1

One simple but overlooked equation in electricity is:

    E = I x R

It is simple but it is the thumb of the rules for electrical stuff
even when capacitors and inductors are involved.

The units involved in this equation are:

Volt (E), Amp (I) and Ohm (R).

Voltage is always measured over two leads of something, such as the two
leads of a battery, the two terminals of a bulb, the two leads of a fuel
injector, the two leads of a fuel pump, a starter, an alternator, etc.

Current (amp) is the electric current flowing inside a wire. To measure
it you need to cut the wire and connect a current meter to the opened
two leads. The current flow into a starter when you crank the engine
could be over 100 amps. The current flowing through an LED light bulb
in the instrument cluster could be less than 0.1 amp.

Never use a current meter to measure voltage. It would be like shorting
the two points that you are trying to measure. If you try to use a current
meter to measure the voltage of a battery that's instant short. You would
experience burn, fire, shock, and smoke. The meter would be destroyed
instantly.

If you try to measure a current in a wire using a voltage meter it would
be like an open circuit. No (actually very little) current would be flowing
through the meter. The meter will show a voltage across the opened two
leads of the wire.

Playing with a current meter is potentially dangerous. Never use it to measure
voltage.

David








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