Al Magnet Wire Motors

Now that my utility is calling Cu a "precious metal" in its anti-wire theft campaign what is the status of Al wound motor development?
Supposedly the WWII era Al motors burned up easily but there shouldn't be any reason why they couldn't be protected very cheaply nowdays.
If a motor costs several cents/watt and develops 1 W/gm a motor and the cost of copper is 1 cent/gm maybe a third of the cost is copper.
Bret Cahill
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One reason is no one is going to give up even a little of the 95% efficiency of Cu windings for just one cent/watt, the cost advantage of Al.
Bret Cahill
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Figure the cost of the electricity is an order of magnitude greater than the cost of the motor, maybe 30X more than the copper at current prices and even a 1% decrease in efficiency isn't worth the capital cost savings.
Al will probably never be more cost effective.
Bret Cahill
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Bret Cahill wrote:

Aluminum wire requires different connectors than copper. It expands and contracts more with temperature changes. Check with the EEs over at alt.engineering.electrical. They could give you a definitive answer.
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Al also melts a much lower temperature but these issues might all be resolved with proper design and controls.
At least one killer is the conductivity of Al is 30% less than Cu which means the coils in an aluminum motor wouldn't pack as tight for the same current & field and the motor wouldn't be as efficient as copper. Since the cost of electricity over the lifetime of a motor might be an order of magnitude more than the motor itself, the 30% increase in capital cost of a Cu motor over Al can be justified with only a 1 or 2% efficiency increase.
Copper probably can provide that efficiency increase.

OK.
I'll also ask about those "pegleg" transmission line towers that have one wood pole leg and one steel with a wood pole running across the top.
Bret Cahill
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snipped-for-privacy@peoplepc.com wrote:

Perhaps silver could be justified in this application.
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What application? Swindling the ignorant?
A 5% increase in conductivity won't result in anywhere near a 5% efficiency increase, certainly not enough to make up for an order of magnitude or so higher capital cost.
Maybe there is some really coincidencial situation where the only motor that will work must be slightly smaller that what is possible with Cu.
But that's a small market.
Bret Cahill
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It might not even be lighter than a Cu motor, Al's only major selling point besides being a somewhat less desirable target for thieves.

If the cost of electricity went way down then Al might make sense.

If it were close they would be fine tuning their spreadsheets.

Sounds plausible. No one here would waste much time sourcing a matching pole just for aesthetics. Add the cheapest support and call it a day.
Maybe they could save some ground wire with the metal poles.
Bret Cahill
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Bret Cahill wrote:

The resistivity of copper at 20C is 1.673 microhm-cm and its density is 8.96 g/cm3. Therefore if the cross section area of a copper wire is 1.673cm2 it will have a resistance of 1 microhm/cm and the mass will be 1.673 x 8.96 = 15.0g/cm.
The resistivity of aluminium at 20C is 2.655 microhm-cm and its density is 2.70 g/cm3. Therefore if the cross section area of an Al wire is 2.655cm2 it will have a resistance of 1 microhm/cm and its mass will be 2.655 x 2.70 = 7.17g/cm.
It is therefore clear that Al is a far better conductor on a mass basis. Connection is a problem but I was recently reading about a company that claims to have broken all power to weight ratio records with an Al motor. Each coil was a 3/4 turn and built up of 4 custom shaped rods of aluminium. Two of the rods where shaped to exactly fit into the holes in the magnetic laminations. These rods had threaded holes in both ends. The other 2 rods were screwed to the first two rods to connect them together on one side and to the neighbouring coils on the other side.
Sorry but I cannot find the link at the moment.
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That doesn't necessarily mean a lighter motor. The efficiency might drop a lot.

Maybe there is a future for electric airships.

Someone else will.
Bret Cahill
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Where do the efficiency losses come from? The IR losses in the wire dominate. In the example above I made the wire resistance the same in both cases.
The next biggest loss comes from eddy currents in the magnetic material. Why should there be a difference between an Al and a Cu motor? The magnetic field will have to travel a bit further in the Al motor but spinning a little faster will make up for that difference.

Of course there is. Electric motors already dominate the radio controlled aircraft business. That was probably where I read about the Al motor.
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That's not transcontinental transportation but that's not necessarily an argument against all long range turbineless flight either.
Just last week they announced that they discovered a bird that flies 7,000 miles nonstop, the world record for the animal kingdom. Maybe it eats flying bugs on the way but it's still amazing. If a bird can do it . . .
A bird might have to go 40 - 60 knots/hour to get its Reynolds number up to the magic 80,000 -- 100,000 where the drag coefficient drops precipitously. Some birds' feathers must act like dimples on a golf ball.
Have they tried dimples on radio controlled aircraft? The size and speed could designed around N re = 100,000 and dimpling could vastly extent the range of such craft.
Widebodies reach Nre = 100,000 going 0.1 knots so dimples won't work there.

If you could get the specific power up to 5 - 7 kW/kg even sacrificing some efficiency might be acceptable.
Bret Cahill
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On Tue, 4 Nov 2008 10:41:52 -0800 (PST), Bret Cahill
--
It's not "knots/hour", it's just "knots".

JF

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Well, none actually. The only thing that's been done with motors of any kind in the last 50 years is making A.I., Robots, Fiber Optics, and Digital Motor Controllers. Since that not only reduces the motor cost, it's get rid of the wiire theft problem too.

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Aluminum is used in the cast rotors of squirrel cage induction motors to replace copper where cost is more important than efficiency or where the higher resistance of aluminum is indeed more important.
What would concern me the most about aluminum is its apparent tendency to fatigue quicker than copper.
Copper prices have dropped to 40% of their value 2 months ago due to the world credit crisis.
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So there is always _some_ flexing or movement of magnet wire no matter how tightly wound?
Al has no fatigue limit. Sooner or later, with enough cycling, it will crack.
Steel would be even cheaper and the strains could be designed under its fatigue limit. It could then cycle forever without breaking.
Does copper have a fatigue limit?

Same if not a bigger drop for Al.
Bret Cahill
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On Nov 6, 4:05am, snipped-for-privacy@peoplepc.com wrote:

There are physical stresses on the coil due to the magnetic forces.

I presume you meant it HAS a fatique limit.

Unfortunately its conductivity is vastly lower; it is however common to include steel wire in the multistrand core of overhead transmission lines. Motors are however wound with single strand wire.
I understand what you mean about the lack of fatigue limit. It would no doubt be possible to make a steel wired motor as well as an aluminum unit. The question is: what will happen to the wieght, size, cost and efficiency of such a motor?

all metals do bar steel I think. Copper has greater malleability and ductility. Consider the case of copper wiring for housing which once had a reputation for starting fires (presumably becuase installation procedures hadn't been followed or developed). It can be pulled around tight bends and can be clamped into a crude and rather nasty screw terminal without wire protection. Aluminum can cause house fires if treated similarly. At the bare minimum the wire terminal needs protection from the screw (by a flat) and in reality should be ferruled within a corrosion protection paste or grease. I might add that the lastest Airbus A380 transmits its power electrically using aluminium wiring instead of hydraulically.

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On Fri, 7 Nov 2008 04:31:41 -0800 (PST), snipped-for-privacy@yahoo.com.au wrote:

--
Thanks for the info; I'll _never_ fly in an A380.


JF

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Just as worrisome is the hydraulics: there have been many total hydraulic loss incidents. The aviation industry tell you about their 3 or 4 'redundant' hydraulic systems
Japan Airlines flight 123 by failure or pressurization bulkhead bear tail apu. United Airlines Flight 232 by engine disintegration DHL/EAT A300 With No Hydraulics After Being Hit By Missile.
Basically the 'triplicated' hydraulic systems all route next to each other. Should a traumatic event damage all three then they all bleed out. At least with electrical systems circuit breakers disconnect the faulty system. In hydraulics once the fluid is gone then that's it.
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