On Nov 7, 2019, at 2:27 PM, <[email protected]
<mailto:[email protected]>> <[email protected] <mailto:[email protected]>>
wrote:
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..
*From:* Ken Hohhof
*Sent:* Thursday, November 7, 2019 12:15 PM
*To:* 'AnimalFarm Microwave Users Group'
*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.
*From:* AF <[email protected] <mailto:[email protected]>>
*On Behalf Of *[email protected] <mailto:[email protected]>
*Sent:* Thursday, November 7, 2019 12:53 PM
*To:* [email protected]
*Subject:* Re: [AFMUG] OT: Induction coil voltage
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.
*From:*Adam Moffett
*Sent:*Thursday, November 7, 2019 11:47 AM
*To:*[email protected]
*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.
On 11/7/2019 1:41 PM, [email protected] wrote:
Yes, it is one cycle of AC.
*From:*Adam Moffett
*Sent:*Thursday, November 7, 2019 11:26 AM
*To:*[email protected]
*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?
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