Originally posted by 95GS-R
Actually, I challenge you to try it. When you push the defrost button to redirect air flow to the front windshield, the A/C is on. My buddy's 90 Accord does it, so does my Integra. That's how defrosters are designed to work.
Hmm... maybe I need to check some wiring diagrams a little closer...
Are you sure about the commutator. I couldn't imagine using a brush generator in there. If carbon arcing is truly a problem why wouldn't the manufacturer be using an AC "alternator"?? Eddy currents result from simply moving a magnet near a conductor. Sooo, it could be a completely mechanical system, I'm not familiar with automobile ones, but small table top eddy current dynos measure torque based on the physical proximity of permanent magnets to a rotating conductor.
Alternators aren't the same as generators, you can't reverse flow power into an alternator and force it to turn. Regardless though, anytime you apply counter-current to the rotation of an armature, AC or DC powered, you get a high current draw which causes the contacts [brushes, loops, whatever it uses] to try to fuse with the comm and arc as it's seperated. Unless you're talking about a different style or one designed for something other than high-output car engines, carbon arcing is a problem, as well as being able to supply enough current to accurately measure the results. I've seen similar dynos on a much smaller scale, where the arcing problem is much smaller since you're dealing with less nessary amperage for the testing, but for cars, you're talking about some large and high-draw armatures to counter an engine's crankshaft.