On Aug 16, 2009, at 11:41 AM, Harry Veeder wrote:
----- Original Message -----
From: Horace Heffner <[email protected]>
Date: Friday, August 14, 2009 4:55 pm
Subject: [Vo]:BB motor - surprising experiments
I thought one way to validate a back emf is to drive the motor to a
higher rpm and look for an increase in the back emf measured. I
stuck a half inch buffing pad on my Dremel tool and stuck it into
the
partly exposed 1/2" shaft hole in the pulley and revved the thing
up
to at least twice normal speed. I expected the back emf to double
and that trurning on the power would slow down the motor. It
didn't
slow down when power was turned on. If anything it just ran faster
when I threw the switch than where the Dremel tool took the rpm.
It
appeared to take much longer for the filaments to heat up though,
and
the Channel 2 trace in Photo4 below bears this out, showing the
voltage across the current resistor R1 is almost flat at -7 V
throughout the run. The voltage drop across the motor, shown in
Channel 1 is nearly flat also at about 2.8 V. The prior run
stabilized at about 2.7 V, with the stopped motor voltage drop at
1.5
V. This means the back emf only increased by about 0.1 V over the
run in Photo2, even though the rpm doubled, and the motor power
output apparently doubled with no increase in overall current.
From my hysteresis model, I expected torque to increase with RPMs
to
an optimum point where the magnetized material migrates into the
current i such that i * M is at peak strength, and then to decline
as
RPMs increase beyond that point because the material doesn't have
time to be magnetized. What I would not expect is that the back
emf
would not change significantly at all even though the RPMs doubled.
It also appears *superficially* that the motor power doubled and
the
heating of the current resistor dropped significantly, even though
the voltage across the resistor is measured at pk-pk 7.20 V, not
too
different from the 8.8 V for the stopped motor.
Weird. By starting at a higher RPM, the motor runs faster, system
current is less, yet back emf is unchanged. If the motor were not
so
darned inefficient this would be a monumental discovery. The
inefficiency and quirky behavior of the hysteresis effect make
quantifying individual variables difficult.
Photo4: High rpm current start:
http://www.mtaonline.net/~hheffner/HullShuntHighRPM2.jpg
The value of efficiency should not diminish the value of the
discovery.
The sentiment that nature does everything efficiently (and we should
too) arose in the 18th century. I think the idea has come to hinder
rather than help discovery.
Harry
My point above is that the motor's extreme inefficiency masks what is
actually happening, so there is no solid discovery, or at least
discovery is made difficult. I've definitely nailed down the effect
is electromagnetic. I've hopefully provided a conventional
explanation. There is no solid evidence of anything anomalous or
"Marinov" in origin. Sill, I find it a bit curious.
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
