So we packed it back up and sent it to a motor rewind shop, where the insulation was burned off in a kiln at high temperature. Then, the technician diagrammed the geometry of the wire connections of the various coils in the wire slots in the armature. This Jake has 47 wire slots in the armature and 94 bars on the commutator that the wire coils are soldered to. The coils were formed with flexible insulated copper “motor” wire and replaced in the slots in the armature, with the coil ends soldered to the commutator in their original geometry. Once rewound, the armature was baked again, but at a lower temperature, which drives off any moisture. The warm armature was dipped in motor-insulating “varnish,” then re-baked to set the varnish. Excess varnish was cleaned off the armature and commutator. The varnish also had to be cleaned out of the slots between the 94 bars in the commutator so that the varnish doesn’t gum up the commutator brushes. Once this was done, the armature was reassembled in the generator and the whole thing was bench-tested again to confirm that it worked as it should. Rewinding is fairly complicated—to say nothing of being tedious—and it’s best left to patient technicians who know what they’re doing. The average rewind shop would likely charge between $1,000 and $2,000—the labor is intensive and insulated copper wire is expensive.
By January, we had a freshly rewound, slightly modified armature. With one extra winding turn and 11 AWG wire instead of 10 AWG, the machine would from then on produce higher voltage at a lower rpm, but have a slightly lower current-carrying capacity. We tested the armature on the bench in Mick’s shop, then reassembled the machine and brought it back to the MREA.
Thanks to an unusually warm spring, we were able to get a crane to the MREA in early March 2012 and reinstall the machine. Mike had repainted the turbine a sparkly royal blue normally reserved for muscle cars. Not only did it look better than ever—but it worked, too!
Little Jake still requires maintenance from time to time, as all wind turbines do (being exposed to the vagaries of wind and weather is tough on mechanical equipment), but we keep it in perspective. You wouldn’t drive your car for months and months without so much as an oil change or a brake check, would you? (If you answered yes, then wind turbines aren’t for you!)
There’s really nothing we could have done to prevent an armature failure. Motion in a generator is unavoidable (if the turbine is actually turning). Heat can be dissipated in various ways, but this is taken care of in the generator design. The best thing an owner can do is to make sure that, in the case of a generator, the commutator brushes are in good shape and seated properly so they don’t arc, since this creates heat. But the environment wreaks havoc on insulated wire, just as it does for electrical wiring in an unheated garage or a chicken coop—so there’s not much you can do, unless you leave your wind turbine parked in your living room.
The other thing that can “prevent it from happening again” is to find a quality rewind shop that uses quality insulated wire and varnish. Cheaping out on these with cheap materials invariably means that you’re going to be at it again until you figure out that this is not the place to cut corners.
Today, Little Jake is nestled behind the Renew the Earth Institute at the MREA on its 100-foot lattice tower, delivering electricity to the premises. We know that it will still require some tender loving care from time to time, but if this armature lasts as long as the original, we won’t have to worry about another project of this caliber until about 2080.
Jenny Heinzen is the curriculum and training coordinator for the MREA. She is a licensed master electrician and electrical inspector in Wisconsin. She works with organizations like NABCEP and RENEW Wisconsin to promote professional installations and supportive renewable energy policies, but her favorite days are those spent on a tower.
Midwest Renewable Energy Association • midwestrenew.org