On 1/22/2013 1:01 PM, hr(bob) wrote:
On Jan 22, 12:26 pm, wrote:
On Tue, 22 Jan 2013 07:36:49 -0800, Jon Danniken





wrote:
On 01/21/2013 07:22 PM, wrote:
Why do Microwave ovens that have a rotating platter, change direction?
The platter seems to usually spin counter-clockwise. However, if I turn
it off to stir or check the food, the platter begins to turn clockwise.
It dont change direction once it's running, only when I stop it and
restart. This is the second microwave I've had that does this, and they
were different brand names.

Not only do I wonder *why* they change rotation, but *how*? I'm
guessing they use a shaded-pole motor (I'm not sure), and as far as I
know, those motors only turn one direction. Either CW or CCW.
Unless there's a belt driving them, there is not much room for any other
type of motor in the base of the oven.

They're just little sync motors, like you'd find in a clock. To save
money, they don't have any provision to determine which way they spin,
so direction of travel is determined by pole proximity.

Jon

Thanks for the info. That makes sense. The direction should not matter
as far as how it cooks, since the cooking is done by the magnetron. The
rotation is just so it cooks evenly. That much I knew. Now I know why
it changes direction.- Hide quoted text -

- Show quoted text -

And in the similarly-designed clock motors, there is a little
mechanical gizmo that won't allow the motor to run the clock
backwards. The motor will try to run backwards, the try forward, and
then the gizmo lets it proceed.


A sprag clutch. ^_^

http://en.wikipedia.org/wiki/Sprag_clutch

TDD