real electric motors work
Taking motors apart.
is not an exhaustive list. Always take extreme care when
working around machinery. Wear protective glasses and think
before you act. Below are a few safety tips that are important
to observe when working with electric motors.
Before disassembling an electric motor, make sure you have
owner's permission. This is really important – especially
if you don't succeed in getting it back together again before
they find out.
Disconnect the motor from the source of electricity. In
necessary, cut wires off to ensure there can be no accidental
reconnection. Never fool about with the mains.
In the case of permanent magnet motors, the magnets can
be extremely powerful. Parts of the motor can unexpectedly
slam together, trapping fingers and other sensitive body
parts, or striking the eyes with metal splinters.
In many permanent magnet motors, simple disassembly and
reassembly, even if you do it 100% right, will result in
the magnetic field being weaker than before. Paradoxically,
the motor will now spin faster than it did previously.
This could lead to alarming results if, for example, the
motor is part of your grandmother's electric wheel chair.
This one applies to any large inductor, including the windings
of an electric motor. If you suddenly interrupt a current
that is passing through an inductor (for example, if you
are testing a winding with a battery and then disconnect
the battery) a high voltage will appear briefly across the
winding (V = -LdI/dt). This can kill you. Really. Ensure
that you are not holding the bare wires when you are experimenting,
even if the DC voltage is only 12 volts or so.
All rotating shafts are potentially dangerous - never be
complacent where exposed shafts are concerned. Even a clean,
smooth shaft can easily grab hair or clothing and cause
serious injury. An induction motor inside a vacuum cleaner
is pretty harmless (unless you're a mouse), but the same
motor sitting on a bench is potentially lethal. For a start
it's more powerful than you. Second, it has no common sense.
Finally, remember that the torque the casing exerts on the
rotor is exactly equal (and opposite) to the torque the
rotor exerts on the casing. So, if the rotor is heavy (and
it usually is), when you first switch the motor on the rotor
tends to stay put while the casing rotates. Bolt it down