Is an induction motor a good thing for small appliances?

The one food processor that I've dismembered (Cuisinart) had a shunt-wound (universal) motor, which I thought was an ideal choice since they have such high starting torque. I'm rather surprised that someone would use an induction motor in a single-phase application that required high starting torque -- it seems particularly ill suited.

You are correct that watts and horsepower mean little in consumer appliances, and that they don't express the efficiency of the motor (efficiency is a 3rd measure). Consumers do not regularly check the shaft horsepower of their food processors, so manufacturers can make some pretty silly claims. 700 watts in and 1HP out is particularly silly, unless you're on a sci.physics.perpetual-motion.

I think an induction motor in a food processor is not a good thing, to the point where I question whether that's really what it has. Induction motors, particularly ones for single-phase service, have poor starting torque. You can improve things somewhat at the cost of running efficiency, but not much. Since food processors require _lots_ of starting torque it's hard to believe that they'd use an induction motor.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

Yet, looking at the details of a typical Kitchenaid food processor, that is the type of motor they say it is fitted with.

Ross Herbert

** Gawd - how big is this beast ??

My bench grinder is only 1/3 HP.

** Watts indicates the electrical power consumption while HP indicates the mechanical power out.

Seems that two different test methods have been used since 1 HP = 746 watts .

** Induction motors have very long, maintenance free lives - plus they are nice and quiet.

Nearly all fans, bench drills and large electrical machines use induction motors - so did an amasing Braun juice extractor I once owned.

But, their power to weight and torque /rpm curve is *much* poorer than common "universal" or AC/DC motors you find with hand held power tools, sewing machines, vacuum cleaners etc.

........ Phil

are

There is a trend toward using three phase induction motors in newer appliances, although I thought it would be mostly washing machines and air conditioners. The recent introduction of inexpensive single chip 3 phase VF controllers in the FHP and up to about 3 HP range has made it practical to use three phase motors in non-industrial environments. The motors themselves are very simple to construct, and are extremely reliable and maintenance free, with just a rotor, a couple of bearings, and a stator. No external start/run capacitors are required, and no inefficient shaded poles. No centrifugal switches or sparking brushes to break or wear out. Just a $10 IC, which includes built-in adjustable speed and torque control, soft start, dynamic braking, overload protection, and even regeneration. The system actually works on a DC "link", which could be supplied by a bank of batteries. The three phase motor is indeed an elegant work of art, pioneered by Nikola Tesla over 100 years ago.

Paul E. Schoen

Disregarding any technical aspects, an induction motor will usually last for ever and perhaps more important here is that they are quiet in operation. john

Kitchenaid is a top-of-the-line manufacturer with a well-deserved reputation for producing high performance and durable products. The induction motor and drive technology used in this particular product most likely represents the optimal solution over a feature set comprised of a myriad of factors going well beyond the simplistic prima facie engineering summary data. The modern motor control technology is quickly obsoleting most of the popular conceptions about the various motor types, and it is very likely that this device is capable of 1HP peak mechanical outputs with >90% efficiency. Here is an example of the kind of control technology available at low cost:

So I guess I need to ask KitchenAid what kind of induction motor it has?

In article , Tim Wescott wrote: [...]

You mean series motor. Shunt motors don't work for AC.

--
--
kensmith@rahul.net   forging knowledge

Aaargh. At least I got the 'universal' right.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

Having seen what happens between what I say to a marketing guy and what gets printed, I have to say that I'll believe it when I open one up and see a lack of brushes.

And from the other thread: series-wound. It's what I meant, I just got the other 's' word (d'oh).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

Well, they probably found out that a permanent-magnet motor has even worse starting torque: these are what's used in pumps for washers these days. They turn a random direction (which probably clears debris).

:-)

Thomas