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. On Fri, Nov 8, 2019 at 5:33 AM Mark Radabaugh <m...@amplex.net> wrote: > 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 > > On Nov 7, 2019, at 2:27 PM, <ch...@wbmfg.com> <ch...@wbmfg.com> 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 <af-boun...@af.afmug.com> *On Behalf Of *ch...@wbmfg.com > *Sent:* Thursday, November 7, 2019 12:53 PM > *To:* af@af.afmug.com > *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:* af@af.afmug.com > > *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, ch...@wbmfg.com wrote: > > Yes, it is one cycle of AC. > > > *From:* Adam Moffett > > *Sent:* Thursday, November 7, 2019 11:26 AM > > *To:* af@af.afmug.com > > *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 > AF@af.afmug.com > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > > ------------------------------ > -- > AF mailing list > AF@af.afmug.com > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > ------------------------------ > -- > AF mailing list > AF@af.afmug.com > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > -- > AF mailing list > AF@af.afmug.com > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > > -- > AF mailing list > AF@af.afmug.com > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > -- - Forrest
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