AC motor windings using pure copper vs non copper wires ?

[BravoV]

Recently I've been looking to buy mains AC powered power tool, while browsing for product, some sellers (at least locally here), put a clear note specifically at the AC motor winding material.

From pure copper wire which is the most expensive, down to not so pure copper, like some stated they're copper alloy or brass  , and down to the cheapest variant that uses aluminum wire. 

Question is, what are affected by using pure copper vs aluminum windings ? Power / torque ? Longetivity ? Efficiency ? Etc.

[HackedFridgeMagnet]

the squirrel cage induction motor is the only one that i know of that you wouldn't immediately use copper. AFAIK this doesn't apply to wound Rotor IM.

It has very few turns in comparison it seems they actually cast it.

See the structure section on wikipedia.
https://en.wikipedia.org/wiki/Squirrel-cage_rotor

https://www.eevblog.com/forum/beginners/ac-motor-windings-using-pure-copper-vs-non-copper-wires/?action=post;last_msg=3270340

[T3sl4co1l]

These are essentially equivalent products, only the motor varies..?  I know they're all about squeezing cents from a stone but sheesh...

Needless to say, anyone selling their product based on the purported composition of their windings, is way down in the noise of products anyone wants to buy.  Why do I care what it's made of?  Does it not meet the basic specifications I expect it to?  (Not that these sorts of things give specifications at all.  Again...why do I care? )  Is this an honest signal (it's really made as stated) or just marketing? ("Brass looks shiny, maybe they'll buy brass ones today!")

On the dubious chance that it's honestly made that way:
Most alloys, and brass, have much less conductivity than copper, or even pure zinc for that matter.  Aluminum is fine if the motor is a bit bigger -- more metal (by volume) is needed, and it probably has higher inertia (due to the larger rotor, which is still steel), but it can potentially have less mass than the copper version.  Or put another way, don't expect the power density of copper, buy a few sizes up to get the same power capability.

Resistance in the windings always worsens performance.  There are intentional places to use resistance in motor design, but it is not here.

Examples: the resistance of an induction rotor, which can't be superconducting else it won't trap a magnetic field and start up at all.  Or the shorting bars in some synchronous motors, which dampen vibration (the mechanical phase of a synchronous motor oscillates against mains phase, as a startup transient; bars dissipate this energy, allowing it to settle to the in-phase position).  Or harmonics (say from the perturbation from the slots and windings in an alternator).

Also to clarify, I assume we're talking about universal motors here, as those are probably the most common type for "mains AC powered power tool".

As HFM notes, induction rotors are often aluminum, and from the above, this is one case where losses are intentional.  Copper is pretty (very?) uncommon in this application.  Indeed, the rotor isn't even fully loaded with aluminum, it's merely a "cage".  It seems very little copper indeed would be needed (but probably still not worth the labor, or balancing, of winding it?).

Tim

[David Hess]

Aluminum windings require a larger winding window so result in a physically larger motor but their lower weight is advantageous in some applications.  So it depends on if power/weight is more important than power/volume.

But it would not surprise me the unscrupulous are using aluminum wire for motors designed for copper to cheap out.

[amyk]

As HFM notes, induction rotors are often aluminum, and from the above, this is one case where losses are intentional.  Copper is pretty (very?) uncommon in this application.  Indeed, the rotor isn't even fully loaded with aluminum, it's merely a "cage".  It seems very little copper indeed would be needed (but probably still not worth the labor, or balancing, of winding it?).

They used to use copper for those too. See attached image, it's a book from 1914.

[james_s]

A lot of motors and ballasts were wound with aluminum wire when copper prices spiked during the Vietnam war. The aluminum wound stuff runs hotter and is less efficient, or has to be physically larger for the power.

[BravoV]

Thanks for replies. 

In the context common universal motors, AC mains driven, as the motor size is fixed, and as they just use the same size, when it comes to the windings using copper vs non copper, assuming they used the same wire's diameter and winding count.

Can I summarize it that motor will heat up faster as the wire's resistance is higher on the non copper ? Also when heated, apart from power efficiency which will be affected, cmiiw, also the motor's torque ?