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

"Nigel Eaton" wrote in message


In article lgate.org,
Tom Jacobs writes

and fukky understand the tacho'

I ruv you rong time, ten dorrah!

Sorry, it *had* to be done...


Hi All,

Thank you for all the replies, both in and out of group.
I admit with red cheeks, that I did not read my post properly,
and can only say that the "k" is next to the "l" (well noticed
Nigel, must have been a friedonion slip, but don't aplol
gise, I ruv a bit of mild p taking), but I did spell tacho
correctly twice, and I also made a,mistake in the motor ratings.
The current stated should have been 4.4 A not .4, ie 1KW approx'.
Is the efficiency of the motor so low, I often see 1 HP quoted as
700 ish watts and didn't think about efficiency.

I am trying to get some schem's from the manufacturer of one
of the machines to see what the tacho' is for, and if I do, I'll
share the info.

Best Regards,

Tom.

Nunce excretia in extractum est.


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.

Tacho output voltage or tacho output frequency can be used
to sense motor speed. Early controllers used discrete transistors and
a triac output. Later boards integrated most of the control functions
into a single IC - Motorola TDA1085C is typical.

Jim