Solar A/C

Interesting Idea...

But I wonder just how much energy is lost in a modern DC-to-AC invertor compared with the circuitry involved in an ECM motor..



In the old days, railroad locomotives ran with essentially DC motors on 25 cycle 11,000 volts AC. These motors had brushes on a commutator, so there were problems with brush wear, flashover, and other similar problems. Early Diesel-electric locomotives were similar: straight DC motors supplied by a DC generator (another commutator) on the locomotive. And later electric locomotives had ignitron rectifiers (later, semiconductor diodes) to convert AC from the catenary wire or alternator to DC for the motors.



Recent locomotive designs, though, have used AC from the catenary or AC from an alternator and rectified them with large semiconductor diodes to DC. But the interesting change has been the use of AC wheel motors with semiconductor invertors that are computer controlled. The computer computes all kinds of things and applies the right frequency power to each axle motor. Even the cost of running the invortor is low enough that all this pays off. And we can be talking 11,000 horsepower here.



Part of the reason is that by controlling the frequency applied to an AC drive motor is more efficient that brushes on a commutor of a DC motor. Now it could be said that an ECM (DC) motor is just as efficient, but it amounts to the same thing, at least at high power levels, Of course, on a railroad locomotive, since the computer is there anyway, they also compute wheel slip and adjust the torque on each axle to give just the most efficient level of torque. It turns out that a little wheel slip is desirable (not enough to cause premature wear of the wheels), not a problem with residential size heat pumps, I imagine.