On 26 Nov 2019 at 18:45, forrest.whitmore via EV wrote: > gearing the diff and/or transmission to a higher RPM (within set > safety-margin) allows for less required amps along with less heat? > Initially, I was under the impression that a lower motor RPM > corresponded to a "cooler" motor.
I'm not an engineer, so this is seat of the pants for me (aka "pulled out of my bum"), but I'm sure someone will correct me if I'm off base. Higher gearing means lower motor speed. (Duh.) Generally that means less voltage and more current. More current means more I^2*R heating, from the resistance of the motor and indeed everything in its circuit. Inversely, all else being equal, higher motor speed therefore means less I^2*R heating. In motors with internal fans, higher rpm also means more cooling. Finally, there is the efficiency advantage of operating at the motor's peak of the rpm-vs-efficiency curve, which also means less of the energy wasted as heat. I think you probably want to gear your drive so that your motor is operating at its peak efficiency rpm when you're at your typical cruising speed, and so that the top speed you want doesn't exceed the motor's red line. But that's not usually the gearing you get with an ICEV factory differential. That's why most single-ratio conversions I know of have either locked the stock transmission in a lower gear, or used a custom gearbox. I expect that a 3.27 final drive with no other reduction would call for either absurdly small wheels or a large, heavy, low-rpm motor. Maybe both. What vehicle are you converting? Are any other final drive ratios available for it? Maybe there's a transaxle from a FWD car you could somehow shoehorn in? David Roden - Akron, Ohio, USA EVDL Administrator = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: mail sent to "evpost" and "etpost" addresses will not reach me. To send a private message, please obtain my email address from the webpage http://www.evdl.org/help/ . = = = = = = = = = = = = = = = = = = = = = = = = = = = = = _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub ARCHIVE: http://www.evdl.org/archive/index.html INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
