Electric Motor Windings

Yep, it's used. It's a lot cheaper, but it does take more room (or builds up more heat - take your choice). They're a bear to repair.

The critical factor is the electrical conductivity of the metal. At room temperature Copper has conductivity of 59.6*10^6, Aluminum has 37.8*10^6 but the highest is Silver at 63*10^6 all with a unit of Siemens/meter. (Remember to convert a certain amount of wire made from each of these metals into the conductance [inverse of resistance] you multiply the appropriate number by the cross sectional area of the wire and then divide by the length of the wire.) So with copper being cheaper than silver, by a lot, there's little advantage to using silver instead of copper because its less than a 10% difference between the two electrically. Now with the notable exception of the winding for the shaded pole in a motor, aluminum will only rarely be used for motor windings.

Next time when ever you witness a dis-assembled motor, please closely examine its rotor.

The squirrel cage rotor ought to have flushed with the rotor surface alluminium or alloy rods (use of copper is rare).

Thanks all. I got my daily dose of knowledge.

Mr. Ronseto, its not new to me and the Nigerian people. High cost of copper in this case was not the issue but that of the griddy Nigerian importers and their Far East cohorts.

Electricity in Nigeria for the passed 10 years and up till now can not be relied on for any thing, industrialist bought things in the name of generator (that turned around to witch hunt them) to sustain their production. Some of these generators imported from Far East and cannot sustain a four hour production; has aluminium coils in the field and exciter slots.

For most of them the name plates were falsified to assume a desired value. So many of these machines gave up on commissioning test.

There is no way same casing with same slot type can serve for copper and aluminium on equal rating. This is what I saw importers colluding with outsiders to doup my country men. No apology as a 25KVA ganarator will look a like out side but with copper or aluminium inside and no different in cost.

Actually there is nothing bad with using aluminium wires, but people should be informed to enable them make their choice ahead of time rather than the manufacturers keeping quite on important issues as that.

Motors with aluminium conductors are bigger in size when compared with an equivalent copper wound type. The sound and heat level is also very reduced when compared with copper type motors and generator.

Aluminium wound motors has some few advantages over that of copper. The major disadvantage is the outrageous size when compared with copper wound motor of equal rating.

Dickson

Yeah, I wouldn't want one if i could help, but they are being built, and it's gonna get worse. Doit Industrial in Zhejiang Province does it for pump motors.

Aluminum windings have been around for several decades in electric motors, generators and transformers.

The big welder manufactures Miller and Lincoln, and a few others, use aluminum windings in many models of their welders and have for several decades now. Same with many of the lower end electric motors made by all motor manufactures.

They use a colored enamel so that they look like copper until it gets stripped off. Lincoln and Miller went so far as to copper clad the ends of their welder windings so that they could solder them and claim copper used though out in their advertising in the 70's and 80's.

Due to that little cover up I have a good friend who got stuck with several semi loads of "copper wound" welders both made by Lincoln and Miller that are not cost effective to scrap out due to the "copper windings" being nothing more than copper plated aluminum which is worthless in recycling!

A 100 pound secondary winding of all copper may be worth around $150 - $300 when processed but that same winding in aluminum is worth less than 1/10 of that at best.

tcmtech,

In your experience, have you noticed a "fatigue factor" with aluminum windings?

Failure due to movement of the conductors during high inrush (starting)?

I have not seen so much failure from physical fatigue but when I worked for Praxair as a welder service tech every model of welder that used aluminum windings had problems with the ends of the windings getting loose and burning up at the connection points.

The other common problems are the enamel insulation breaking up and pealing off of the wire from the higher heat and greater expansion levels that aluminum has associated with it. Plus it tends to be far more sensitive to corrosion from air born moisture and other common airborne chemicals found in commercial and industrial locations.

There is now a copper clad aluminum wire that is supposed to be good for that. It is also able to be soldered. It has greater conductivity than solid aluminum but not quite as good as solid copper. It is also being used as voice coils in speakers.

I presume that in the case of speaker coils its use is beneficial in lowering the mass of the coil which gives a dynamic performance increase . Copper in motor windings is always the best choice and it has a a greater fatigue factor than aluminium.

Agreed that copper is best choice- however my arc welder(WIA) has alum coils & has never let me down-as with any welder observe duty cycle. Our State owned electricity supplier has always used alum wire wound around steel centre wire for distribution lines. All commercially available tv antennas use alum tubing. My own antenna is made of copper rods(6) & is far superior to any commercial design, also being multi band & also analogue & digitally capable- & is about a foot long. Alum has better weather resistance than copper, so my ant is painted with red enamel(Icall it Red Antler)- there's a clue!.

Would a copper clad aluminum wire exhibit a "skin" effect due to the difference in resistance that would result in a greater percentage of current being carried by the copper cladding?

Probably something like a skin effect will happen with different current densities will happen. While I clearly underestimated the use of aluminum in my first post here, the conductivity numbers are still valid. Since aluminum is about 2/3 the conductivity of copper, if the cross sectional area of the aluminum is 2/3 of the wire conducting area and the rest is copper, then the currents though each of these will be roughly equal. But I would not expect that copper cladding to be that thick. So I would expect that most of the current will be through the aluminum.

Hmmm maybe the ratios will not be precisely what I conjured, but I think the conclusion will still hold. I'd have to go back to some skin effect equations to be certain of the ratios.

The "skin effect" is really only a factor to consider when the frequency of the current is rather high, at audio frequencies and below it is virtually non-existent except for very large diameter conductors. That said, the difference in conductivity between the copper and the aluminum will give you a certain amount of "layering" of current densities.

The problem with Aluminum wiring is the Coefficient of Thermal Expansion. Aluminum expands nearly twice as much as copper does for a given temperature rise. This expansion poses issues for connections, since bare aluminum cannot be soldered easily and copper clad aluminum will eventually experience issues of the cladding separating due to the shearing forces created by the expansion and contraction. There are connection systems that can be used with aluminum but they are usually for connecting aluminum to aluminum. This expansion and contraction is what caused thousands of house fires back in the 1970's. Copper became extremely expensive so home builders used aluminum wiring. but the screw type and friction type connections were not compliant enough to deal with the expansion. the conductor expanded and since it was constrained by the head of the screw it flattened out. then when it cooled there was a gap that led to arcing, then fire. in large windings, this expansion will lead to chafing of the insulation leading to shorts. this can be dealt with but it takes a lot of design ingenuity to do so.

It would be negligible at the mains supply frequencies. Also the amount of copper would be fairly thin compared to the overall cross section.

Its use in welders is ok as the style of winding is open for cooling so there is plenty of room for the larger cross section. However the big problem area is where connections are made and failure at these points due to overheating metal distortion ,oxidisation and fracturing of the aluminium due to vibration. carefully assembly can avoid most of these problems but as Murphy's law goes!!

Long time back there was one the small scale mfr. of electric motors who had introduced aluminum wires for the stator windings of the smaller motors. His motors were performing well but they had bigger frame sizes and hence bulky.

Occasionally we run into the changes in the way things used to be, But recently I was giving a young man all my abused motors to strip for the copper windings and had accumulated a number of Appliance Motors, Washer/Dryers/air cond. and so on. I got the idea he was getting rich so with my cutoff saw I sliced one in half. I slung alluminum all over the shop and even wondered for a moment where did all the solder come from. I told him and was informed that most all newer appliance motors were copper clad alluminun windings. As Mama Cass would say," Theres a new day dawning"