ROBERT wrote:
Thanks. Lee. I need to study your reply. I need to get to work.
You're welcome! This is a complicated subject. Remember, electric motors
and inverters have had 100+ years of development by some of the
brightest minds in science and engineering -- all the way from Edison,
Tesla, and Steinmetz to Alan Cocconi and J.B Straubel today. You're not
going to pick all of that up quickly. Truly, we stand on the shoulders
of giants.
What helped me get past all the competing theories and confusing
descriptions was to do my own little experiments and tests. I got an old
4-channel audio amplifier, and an assortment of little 24vac AC motors
(aircraft motors, TV antenna rotator motors, etc.)
I generated AC waveforms with hardware circuits on a solderless
breadboard (and later, a little microcomputer). I amplified them and
applied them to the motors. I rigged a motor-generator setup with a DC
generator as the output, so I could easily load it and measure power. I
measure things with an oscilloscope and a motley collection of meters.
A few things I learned:
- You don't need expensive equipment. I probably spent less than
$200-$300 on the whole thing.
- Audio amplifiers wildly exaggerate the power they can provide.
(I blew out a lot of output transistors.)
- There is only about a 10% efficiency benefit from perfect sinewaves
vs. plain old "modified square wave" inverters.
- The benefits from "smart" inverter algorithms (that carefully
optimize the precise voltage, frequency, and waveform) are in
the "corner" cases -- starting from a dead stop, minimizing
noise or torque pulsations, etc. "Close" is good enough for
just driving down the road.
- Getting honest AC measurements is tricky. It's easy to get fooled
by cheap meters and bad measurement technique.
- Consumer-grade motors have low efficiency (like 70%), no matter
how you drive them (no magic efficiency cures).
Once I had a intuitive understanding of how it all worked, I built a big
SCR inverter and used it to drive a 15KW aircraft alternator as a motor.
I ran this in one of my homebuilt EVs. It worked, but wasn't any better
than a plain old forklift motor and PWM controller. The technology was
too early, I was too inexperienced, and I didn't have the resources
(budget) to perfect it.
--
Teaching children to program goes against the grain of modern education.
Just imagine the chaos if they learned to think logically, plan, create,
implement, test, and execute!
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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