writes:

On Wed, 30 Jul 2003 21:30:05 +0000 (UTC), "Tom Jacobs"
wrote:

Many of the early UK front loading washing machines used multi
winding squirrel cage capacitor start and run induction motors. These
had typically a high power (about 1/3HP) 2 pole winding for the spin
cycle and a low power (about 1/8 HP) 6 or 8 pole winding for low speed
wash cycle. Because these were induction motors the natural speed
regulation was quite good and electronic control was not needed.

Later machines needed a lot more power for the high speed spin
cycles and these used high speed series wound commutator motors
because these can deliver much more power (1/2 to 1Hp short term
rated) for a given size and cost. The natural speed regulation of
series wound machines is inherently poor and electronic control is
essential for washing machine service. While crude form of speed
control is possible by sensing the back EMF of the motor this is not
good enough for the wide range of speed and loads needed for the
wash/spin cycles. Because of this pretty well all motors are fitted
with a "tacho" (tachometer) which is a very small (and very crude!) AC
generator which produces an electrical output directly proportional to
speed. A closed loop electronic speed control is used to adjust the
power input to the motor until it delivers the the desired speed
sensed by the tacho output.

Sorry, don't take this as a criticism or anything more extreme but why
do European washers need so much more speed for the spin than American
machines? As far as I know, we are still happily using induction motors.
And, no it's not the difference between 50 and 60 Hz.

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