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First recorded activity by BoatBanter: Jul 2006
Posts: 1,445
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17' Mahogany runabout just completed
wrote in message
...
On Thu, 29 Nov 2007 12:21:27 -0600, Vic Smith
wrote:
On Thu, 29 Nov 2007 13:12:52 -0500, wrote:
On Thu, 29 Nov 2007 12:05:58 -0600, Vic Smith
wrote:
On Thu, 29 Nov 2007 12:59:14 -0500, wrote:
Rare earth magnets?
Excuse my ignorance on this, but is that like Kryptonite?
--Vic
No.
Another big breakthrough in electric motor efficiency is PWM, or
"pulse width modulation" used for controlling the speed. In the old
days, you slowed down a battery powered motor by using a resistor. PWM
slows down the motor without wasting nearly as much energy. It offers
no savings at full throttle, but anything below that, it conserves
power rather than simply converting it to heat. This was a big deal
when they started using it for electric trolling motors about 20 years
ago.
That may well be what I read about. I was going to mention something
about "resistor" or "rectifier" but since I am so unversed on electric
components didn't want to muddle it up.
I do recall that the use of the innovation went beyond trolling
motors, and that it basically applied to all motors, but the article
gave emphasis on industrial use because of power cost savings.
--Vic
It's actually a pretty simple concept. Rather than reducing voltage
with a variable resistor to slow the motor, you maintain the voltage,
but pulse it on and off very rapidly. You vary the motor speed by
varying the duty cycle of the pulses between longer or shorter bursts
of power "on" or "off". The motor is pretty dumb and can't tell the
difference.
Silicon Controled Rectifier or "SCR". Two basic types ... phase angle fired
or zero crossing. The zero crossing type generates less EMI and is
electrically "quieter".
They replaced the old variable resistance "rheostats" for light dimmers and
induction motor speed control (such as in ceiling fans, etc.)
Going back to Vic's question .... I think it was GE that introduced a super
efficient induction motor years ago for use in refrigerator compressors,
etc. I don't remember what made them more efficent though.
Eisboch
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