Electronics > Projects, Designs, and Technical Stuff

Making an induction motor go crazy fast.

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schmitt trigger:
As I mentioned earlier, this could well be a photonicinduction-grade experiment. Which means over stressing it to destruction to determine what would fail first.

That would be a fun video to watch.....with the proper precautions in place.

Mechatrommer:
usually the weakest point is the bearing, if it has sleeve inside, its the one usually go clunking first from inside on overheat or overspeed stress. the rotor shaft usually indestructible you can repurpose it as stone punchers for a while if shaped correctly. and good brand will balance the rotor from factory, you can hear minimal sound in OP video even several magnitude more rpm than designed, this indicates well balanced rotor.

duak:
In some BLDCs the rotor magnets are held in place with adhesive only - there's no radial restraining ring or framework.  These have a definite RPM limit.

I help out a friend who owns a CNC machine shop.  A couple of his machines have high speed spindles that run at 12 K and 20 K RPM instead of the more common 6 K to 8 K RPM.  These are induction motors rated for 10 to 15 HP continuous and usually have chillers to keep their cool.  I've never seen what's inside and don't know how they're beefed up for high RPM.

The spindles on these machines are something else.  They have matched pairs of ball bearings about 125 mm OD with 75 mm ID to clear the tool clamp assembly.  The oil is super thin and is not much more viscous than kerosene or diesel fuel.

Berni:
I would certainly love to see it spun to violent destruction just to see what it is like.

But its possible that the failure ends up being less exiting in the form of burned up windings. The resistance the fan creates goes up exponentially so the amount of power needed to spin it even faster keeps going up faster and faster. At the same time core losses get bigger and bigger as frequency is raised, causing the efficiency to begin dropping. So the required power to get it going even faster might eventually be too much for the windings and cause them to overheat.

Tho catastrophic mechanical failures are a known hazard with externally exited brushed motors where loosing excitation causes them to run away and spin faster and faster until tearing themselves apart.

jmelson:

--- Quote from: Circlotron on August 29, 2019, 01:16:19 pm ---^^ Thank you for that.
I hadn't actually considered that possibility.  :phew:
That experiment is now terminated.

--- End quote ---
A guy at a flight instrument test shop was killed some years ago when he accidentally connected a 12 V aircraft gyro to 24 V DC.  It exploded and pieces hit him in the neck.
So, it CAN happen.

Jon

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