|
You know we might be in trouble if the NHTSA starts mandating
shrapnel containment in future electric cars.
bp
<part15sbs{at}gmail{dot}com>
On 11/11/2019 9:39 PM, Forrest
Christian (List Account) wrote:
I go to a conference every year put on by Microchip
Technologies where a lot of us who use Microchip
microcontrollers take classes put on often by the people who are
designing the actual products we're using.
Like every other conference, a big part is to meet and
discuss things with other attendees. I always love when I
end up sitting at a table by people who do high-powered motor
control, typically brushless anymore. They always have good
stories to tell.
Apparently you've never experienced life until you have
your code unintentionally attempt to lock a rotor on a very
very big DC motor. The stories about having a motor
self-destruct on a test rig as a result are just scary. I
think I can skip that portion of my life experience.... thank
you very much. I do enough unintentional destruction of
electronics myself without needing to add shrapnel to the mix.
For our EE power class
(motors, generators, etc.) they decided we should take a lab
exam. My exam time was for the second session. When the
elevator door opened on the lab floor the burnt electrical
smell was pretty obvious. Professor comes walking out of
the exam with an armful of equipment heading for the tech
repair shop shaking his head and muttering something about
“this was a really bad idea”.
One would think senior level electrical engineering
students would know not to yank banana plug patch cords
out of DC motors running at full speed. Or not try to
uncouple a paralleled generator by adjusting the power
factor to 0 (for those of you not EE’s that leads to two
generators trying to rip themselves apart). Or measure
voltage with a ammeter.
Mark
In our motor lab someone asked the prof
something similar like reversing polarity to
a DC motor that was fully wound up.
I don’t remember the exact question or
exactly what he did but I do remember the
result.
The motor tore itself from its moorings
and launched across the room..
Sent: Thursday, November 7,
2019 12:15 PM
Subject: Re: [AFMUG] OT:
Induction coil voltage
I was an EE
undergrad long enough ago that we had a
required course called
“Electromechanical Devices”, and
popularly referred to as “Motors”. It
had a lab, and none of the professors
wanted to teach Motors Lab, so it
usually fell to the most junior prof,
who didn’t want to be there.
We had one whose
standard answer to all questions was
“Let’s find out.”
Student: What
happens if you open the field coil on a
running DC motor?
Professor: Let’s
find out.
Student: What
happens if you short the output of the
generator in a motor/generator pair?
Professor: Let’s
find out.
Who can guess what
we found out?
Hints: a high
pitched whirr, and a sudden thunk, were
involved.
I used to
have a flashlight that had a
coil and magnet just like this.
Shake it for a while and charge
a cap that is used to light the
light. Can’t remember if you
could shake it and make light in
real time.
But yeah,
you can certainly use a
rectifier and cap to make DC for
a DC motor.
Sent: Thursday, November
7, 2019 11:47 AM
Subject: Re: [AFMUG] OT:
Induction coil voltage
A
future project is going to be a
primitive motor powered by a
battery....I wonder if I can
shake this bugger to make the
motor spin.
Yes,
it is one cycle of AC.
Sent: Thursday, November
7, 2019 11:26 AM
Subject: Re: [AFMUG] OT:
Induction coil
voltage
So
by the way, this
activity works with a
4oz (800+ feet) roll of
30AWG wrapped around the
paper towel tube.
My
next point of confusion
is this:
An
LED obviously has a
polarity. If I connect
one LED to the coil and
drop the magnet through,
the LED lights for a
moment. I expected that
if I drop the magnet N
first and S first that
it would light up one
way and not the other.
Instead the LED blinks
whichever way I drop the
magnet. So does that
mean I am getting A/C
power with this? Do I
get current in one
direction with the
leading edge of the
magnetic field passing
through the coil and
then current the other
direction as the
trailing edge of the
field passes?
I
ran out of time last
night before I got to
the point of hooking up
both LED's. So if this
is A/C then the
difference would be
which color blinks first
I suppose.
The
point of this was to
teach the kids something
about electricity, but
it's turning out that my
knowledge on these
fundamentals is pretty
superficial.
-Adam
On
11/3/2019 12:19 PM,
Adam Moffett wrote:
I
wanted to do this
science experiment
with the kids. My
problem is my LED's
don't light up. It's
from a discontinued
textbook. Apparently
they sold a kit with
the materials for all
the projects, but
that's no longer
available so I'm
scrounging in the
garage.
I
put a volt meter on
the rig and I was only
getting 6mV when I
dropped the magnet. I
doubled the number of
coils on the tube and
then doubled the
number of neodymium
magnets and I'm
getting closer to 30mV
now, but I need closer
to 2V to light up an
LED, so I'm wondering
what would increase
the voltage by two
orders of magnitude.
Is it based on the
number of turns in the
coil?
<image001.png>
--
AF mailing list
[email protected]
http://af.afmug.com/mailman/listinfo/af_af.afmug.com
--
AF mailing list
[email protected]
http://af.afmug.com/mailman/listinfo/af_af.afmug.com
AF mailing list
[email protected]
http://af.afmug.com/mailman/listinfo/af_af.afmug.com
--
|
