| Electronics > Projects, Designs, and Technical Stuff |
| Making an induction motor go crazy fast. |
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| Circlotron:
Got a small 3-phase 6 pole induction motor that normally runs at 1000rpm @ 50Hz. Generated two sine waves 60 deg apart with the function generator and fed them to a pair of class D audio amplifier modules running on +/- 65VDC, then to three toroid step up transformers with 28V primaries in delta and 240V secondaries in star. One corner of delta primary is grounded. Gradually wound up the frequency and voltage until the speed would increase no further. 860Hz and 16,800rpm. Showed it who's boss! Steady speed https://youtu.be/nZZi1qC4d_c Rundown to stop https://youtu.be/SVhdQFP8hGA |
| Ian.M:
Are you trying to get a Darwin Award? You are <expletive> lucky the motor rotor didn't grenade. It only takes one rotor bar to bow by a couple of mm or break at one end or a bearing to catastrophically fail and the rotor will seize inside the stator, and tear the motor apart. Assuming a 2" dia 2" long rotor, at 16800 RPM, the rotor rim speed is 100 MPH, there's over 8000 g of centripetal acceleration, and 500 J of kinetic energy. At the very least, a sane person would want containment round the motor that could safely withstand half the motor rotor mass hitting it at half the rim speed, and trap any high speed bouncing small parts. Edit: corrected assumed rotor diameter - I did the math for 1" radius (and assumed a uniform steel cylinder for the K.E. calculation, so somewhat of a spherical cow). |
| Circlotron:
^^ Thank you for that. I hadn't actually considered that possibility. :phew: That experiment is now terminated. |
| Ian.M:
No need to terminate the experiment. Simply put the motor in a stout cardboard box with plenty of sand bags round it to a thickness of at least 10 times the rotor diameter, and a viewport of 1/4" or thicker clear polycarbonate (don't use acrylic or polystyrene as they aren't shatter resistant) in line with the motor shaft and well anchored to the box and sand bags with gaffer tape. Why cardboard, not steel, plastic etc.? Well you want any fragments to rip through it and dissipate their energy in the sand, not bounce and try to take out the viewport. |
| schmitt trigger:
This appears like an experiment which Youtuber Photonicinduction would love to do. Another solution would be to watch the experiment thru a remote tv camera, while you shield yourself behind concrete walls and/or LOTS of distance. I like Ian's cardboard idea. A large water tank would also be effective in absorbing the shrapnel's energy. |
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