Although the earliest practical DC motor was built by Moritz Jacobi in 1834, it was over the next 40 years that men like Thomas Davenport, Emil Stohrer and George Westinghouse brought DC machines into industrial use.  It’s inspiring to realize that work-ing DC motors have been around for over 160 years. For the past century, DC machines over 30 or 40 kW have been cooled in the same manner – by mounting a squirrel cage blower directly over the commutator.

Whether an old or new design, lowering temperatures is based on the same principles. I've often commented on how fortunate we are to work on such a variety of electric motor designs. One day, you are working on a new design some designer has recently created, and the next day you are repairing a motor that could be in a museum. It's fascinating to see the different ways engineers have devised to do the same thing, and yet reassuring to see how many things remain unchanged even after a century of electric motors. One aspect of electric motors that could be placed in both categories is the way an electric motor is cooled. This article takes a look at how motors are cooled and how we can improve cooling for some of the special applications we encounter.