Seth <[EMAIL PROTECTED]> wrote: "AC doesn't fail you in the middle with a single speed it is at either end. The motor overspeed end and the roll backwards down the hill end. Either pick one of those to avoid, or buy bigger $ilicon. The motor isn't the transmission, it is the IGBTs that are the transmission, and they aren't free. And they come in multiples of 3."
I had a hard time with this note; it infers the inverter doesn't want to provide the Amps at motor stall. The inverter shouldn't care as long as its heat is under control. It limits the current much like the carburator throat limits fuel-air mixture. The motor is the analog of a transmission simply converting power from electric to torque. I think you are saying the silicon can't take the current at low rpm, but it doesn't care. The motor though is all I^2 R loss at 0 rpm and has a bigger heat rejection problem. If the inverter cuts back at low rpm, that's just because the designer wants to protect the low mass motor. The lower frequency may generate more heat I guess..... The extreme grades you mention logically would want use of a lower gear. But these loads also don't last long and the motor can store the excessive heat generated over a few seconds. Or am I missing the point ? ______________________________________________________________________
