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 >> <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 > <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
