Bill wrote:
> In article >,
> "Del Cecchi" > wrote:
>
>
>>If the wire in the windings is small and cheap, you can
>>suck a lot of watts that get converted into heat and not output from the
>>motor. And if there isn't much steel in the motor, again to save money,
>>it might saturate and let the current shoot up and not do much useful
>>work. Ever wonder why an immersion blender might say to only run for a
>>minute continuous? Or why kitchen aid mixers don't want to be run too
>>long continuously? How many of the "600 watts" of my new pro 600 go into
>>making the motor and case hot? Gets pretty warm in about 10 min. What
>>is the specific heat of a kitchen aid mixer?
>
>
> Well, its all about being in the general ballpark with kitchen
> appliances, because if you are worried about 20% of performance, then
> you are probably engineering it too tightly. The variable nature of the
> material as well as the variable nature of the processes you are working
> with would indicate a higher factor of safety in selecting the right
> tool for the job.
>
> The fact that efficiency varies according to a motor's loading and speed
> indicates that you are unlikely to be driving it at its most efficient
> point of operation anyway.
>
> I agree with most of your points above, but a sheet detailing the
> details of the motor's characteristics going to be useless to almost all
> customers. Manufacturers may offer 'professional' models with higher use
> duty cycles, larger motors, or stronger construction, but even then
> there are no guarantees about performance. Thus customers will buy the
> 'standard' model or the 'professional' model and that's all they
> generally want to know (OK, so we know you're not an average customer).
>
> I would agree that labelling with VA (not power) ratings for an
> appliance do not accurately tell the purchaser how much useful work you
> can get out of an appliance, but it can get you in the ballpark in
> comparison against other models of similar appliances. If this is really
> important, you should get/measure the torque/speed curves of that
> appliance, and match it up with the expected duty cycle for heat
> dissipation and then make your decisions based on that. And even then,
> the design of that appliance may make it less desirable than another
> with a lower useful power output, especially if the other appliance can
> make this available power achieve the end result more efficiently.
>
> I fear that this discussion on motor efficiency is a bit like debating
> how many angels fit on the head of a pin.
>
> Bill

Hardly. If one reads the Cooks Illustrated mixer test one sees quite a
difference between a 5qt KA and a 5qt Hobart in performance, even though
the wattage is similar. Likewise KA makes a big deal about the 300 watt
vrs the 325 watt vrs the 350 watt.

So watts is not an especially useful measure. If that is what you were
saying above I would agree with that. The whole small appliance spec
business reminds me of cheap stereo equipment. This amp will do 500
watts peak power.

del

--
Del Cecchi
"This post is my own and doesn’t necessarily represent IBM’s positions,
strategies or opinions.”