Al Magnet Wire Motors

On Fri, 7 Nov 2008 21:11:12 -0800 (PST), snipped-for-privacy@yahoo.com.au wrote:


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I wasn't arguing electrical VS hydraulic, I was arguing aluminum VS
copper.
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A fatigue limit just means the material can be stressed an infinite number of times below that limit, i. e. a steel in a watch spring. If a material doesn't have a fatigue limit, i. e., an Al in an aircraft wing, then, no matter how low the strains, with enough cycling, it is 100% guaranteed to crack.
At first it sounds crazy to intentionally design a plane with wings that are 100% guaranteed to, sooner or later, fall off, but the stress profile over the life of a wing is hard to predict, microbursts, rough landings, etc., so using a material with a fatigue limit doesn't help a designer much in predicting reliability. Al structures can easily last longer than steel that occasionally cycles above its fatigue limit.
In actual practice aircraft designers just keep the strains so low that 99.999% of the time the wing will last ten thousand years. Do a cost/benefit risk analysis to optimize your overall odds at survival and wing fatigue failure will be at the bottom of the list.
In fact, lot of lives probably could be saved _overall_ by shifting toward fuel efficiency and away from overly robust wings. The big picture must be spread sheeted.

Alloys seem to have lower conductivities than their pure element parent metals. The conductivity of iron might be higher than a steel but it's too brittle.
What about carbon fiber?

I once rewound a fan motor with copper of the same gauge. I couldn't get the coils tight and the fan never quite had the power of the original. I'm guessing it drew even more current than the original because there was less of an inductive effect to restrict current. Basically it was a short. The number of turns was less than the original but this would also be true for a tight Al coil using the same motor frame.
The effect on the field should be similar for the tight Al as the loose Cu using the same motor frame.
Maybe this could be mitigated somewhat if a motor could be specifically designed for a lower conductivity wire, but there still is no way to avoid at least some loss in efficiency.
. . .

No one mentions it because it was so gradual but the reliability of electric motors has gone way up. It's hard to find a vehicle without power windows and the windows always seem to work.
The relative cost of electric motors for power has always been low. That's why efficiency won't be easily sacrificed for cost. The cost of the electricity passing through a stationary motor running 24/7 is easily an order of magnitude more than the motor itself.
In contrast a rechargeable battery costs at least twice as much as the electricity it will ever hold in its lifetime.
To be sure an EV doesn't run 24/7 but if an EV lasted 100 years the cost of supplying batteries to an EV might cost 20X more than the electric motors.
The place to sacrifice efficiency to reduce costs is the battery.
Either the initial cost must be very low or it must cycle tens of thousands of times.
Bret Cahill
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