Date: Tue, 9 Feb 2010 15:31:28 -0500
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: generators/inverters for camping
In-Reply-To: <20100209092757.CKENT.555097.imail@eastrmwml29>
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At 09:27 AM 2/9/2010, mcneely4@cox.net wrote:
>David, I thought the complaint was not that the output was NOT a
>sine wave, but that the "precision" of the wave was somehow not that
>great. That might be that the amplitude varies, and in a
>non-predictable way? Not knowledgeable enough about generator
>function to be sure, but that's what it sounded like to me. That
>might account for the ability of the thing to drive a tool motor,
>but not to support electronics (which the battery charger, if it is
>recent, almost certainly contains). Make sense?
Not really. Geometry dictates that the output of a coil rotating in
a uniform magnetic field *will* be a sine wave, as the wires in the
coil cut the magnetic lines of force at varying angles from parallel
(no output) to perpendicular (peak output), parallel again, no
output; perpendicular in the other direction, full output but
opposite polarity. At any point in the (constant) rotation the
voltage output will be proportional to the sin of the rotation
angle. I'm going to say (without going back to look it up) that this
phase relationship will always be true, so if someone knows better,
speak up. The *current* is also a sin wave, but depending on the
type of load (resistive, capacitive, inductive, combined) it will
lead or lag the voltage curve by some number of degrees up to 90.
What can easily vary in a small generator is frequency and
voltage. Typical 60-Hz gear is rated to run from 57-63 Hz, way
outside of any normal variation from the power company, and 95-125
volts which is two or three times the typical variation at the wall
plug. ISTM that the tuned-reed frequency meters I've seen on
generators run from 55-65 Hz in increments of one Hz.
This generator also has a 12vdc charging output, with a full-wave
rectifier, smoothing capacitor and output characteristics just like a
standard automotive charging circuit. I'm pretty sure that this
capacitor, #49 on the parts diagram, is the one that the tech rep
mentioned, as a failure there would cause the output to fluctuate
from 0 to full output 120 times a second, reducing charging
effectiveness. However a failure of one of the diodes would be a
bigger problem, as the input to the capacitor would then be two
pulses of one polarity followed by one of the opposite
polarity. Bear in mind, though, that this affects only the DC
charging output. The instantaneous output of the main alternator is
stabilized by the mass of the rotor and rotating engine parts, and
longer-term by the automatic 60-Hz-seeking throttle mechanism.
I'd sure like to see a scope trace of what's coming out of that thing
under loaded and unloaded conditions. I wonder if a high-resistance
connection somewhere in the generating coil and connections might
exist -- that would allow full unloaded voltage, but would start to
drop the output voltage as soon as a load was applied. And of course
would shed heat something like a toaster, but that might not be
noticed right next to a 3.5 hp running engine. 3.5 hp = 3.5 * 0.746
= ~2.6 kilowatts, incidentally.
Yrs,
David
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