Date: Sun, 17 Aug 2014 18:57:35 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: amps in/amps out ??
In-Reply-To: <53F00D14.5020402@colorado.edu>
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At 10:01 PM 8/16/2014, Richard A Jones wrote:
>Anyway, here's my question for the electron jockeys:
>I measure higher amps going INTO my fridge (+) than
>coming OUT (-). I'm thinking that the fridge is using
>power (and putting out heat, noise, etc) and so that
>is OK. But....
Hi Richard,
I'm curious about the specific numbers you saw, and my question is
did you zero the meter in place for each reading? DC clamp meters
are affected by external magnetic fields. If what you observed
wasn't a meter artifact then as others have said the current is
sneaking to ground by another route.
Current is a physical flow of electrons; if they go in somewhere
they're going to come out somewhere else; their quantity is
conserved. The work is done by expending voltage across some
combination of resistance, capacitance, and inductance, all of which
results in some proportionate current flowing; and the magnitude of
the work done is the summation of the instantaneous products of
voltage and current. In a DC circuit at steady state that devolves
to Watts = Amps x Volts.** Think of current as a result rather than a cause.
**In a purely resistive circuit the work appears as heat; in an
inductive and/or capacitive circuit magnetic and electrostatic
effects allow physical work to be done (which if you follow it long
enough eventually degrades to heat). All practical circuits have
some degree of inductance and capacitance; and all except
superconducting ones have resistance. Your local MRI machine
contains a massive steady magnetic field caused by a permanent
current in a superconducting coil which, once established, will
remain as long as the liquid helium is replenished a couple times a
year, keeping the coil at a temperature ridiculously close to the
theoretical minimum. If the helium runs out resistance returns and
all the work done in establishing that current reappears abruptly as
heat and other effects of the collapsing magnetic field.
DC motors operate by either mechanically (commutator on the motor) or
otherwise (electronic brushless motor drive circuit) simulating AC
such that the appearance or actuality of a rotating magnetic field is
created in the motor which acts against another one that's either
fixed or rotating. Both of those fields can be generated or one can
be derived from one or more permanent magnets. A typical small DC
motor has fixed permanent magnets in the shell and a rotating field
in the armature generated by shifting current to different windings
as the armature rotates. If three windings are employed then the
motor will be self-starting as the active winding never aligns with
the permanent field. Brushless DC motors (box fans, hard drive
spindle motors, CD/DVD drive spindle motors etc.) operate like
3-phase AC motors by arranging drive coils in some multiple of
three. The thee sets of coils are electronically driven sinusoidally
such that each set is out of phase by one third of a cycle with the
other two sets. This creates the effect of a rotating net field
which acts on a multi-pole permanent field in the armature (actual AC
motors usually generate the armature field on the fly rather than
using permanent magnets).
Yours,
David
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