Why are some transformers wound with aluminum instead of copper?
This is mostly a matter of economics in which some manufacturers try to cut cost by reducing quality. An aluminum wire of the same diameter or cross sectional area has only about 60% of the conducting properties of an equivalent size copper wire. However, aluminum weighs considerably less than copper and if you treat the two metals on a pound versus cubic inch basis, there are about 3 cubic inches of aluminum for each cubic inch of copper. Since both metals are purchased on a cost per pound basis some manufacturers use aluminum, even though the resulting transformer is substantially larger than a quality copper transformer. Not all types of windings nor all sizes of transformers lend themselves to be adapted to both aluminum and copper windings. Transformers with aluminum windings must be oversized to the load and generally have about one fourth the life of a quality copper wound transformer. Aluminum wound transformers perform best in constant load applications and should not be used
Aluminum is used on transformers for economic reasons. Equivalent resistance aluminum conductors are larger (by about 2 AWG sizes). The aluminum transformer tends to therefore be slightly larger. Modern termination methods eliminate any aluminum oxide problems. Generally, performance and life expectancy are the same for copper and aluminum transformers.
