On Aug 5, 2014, at 2:25 AM, EVDL Administrator via EV <ev@lists.evdl.org> wrote:
> On 4 Aug 2014 at 18:14, Ben Goren via EV wrote: > >> He says it's okay to spin the motors faster than 8000 RPM so long as >> it's not the controller that's sending the current to the motors that's >> doing the spinning. > > I wonder why this would be. Bill said that the 8000 redline was a limitation of the (Curtis 1239-8501) controllers, and not a mechanical limit of the motor itself. He suggested that the controller might or might not behave gracefully if the motor was spun past 8000 RPM, but that there's no problem in having a powered-down motor and controller spin faster. Still, the math works out such that a roughly 5.7:1 overall gear ratio for the electric motors puts the 5000 RPM peak of the power and torque curves right at 65 mph with a top speed of about 105 mph at 8000 RPM. I'm having an hard time imagining wanting to go that fast any time soon. If I ever want to go faster, at that point I can worry about changing gearing, or getting fancy with GEVCU, or upgrading controllers or motors or whatever other expensive or insane option catches my fancy. I was more interested in the question in terms of targeting an even lower gear ratio; what if that 8000 RPM were at, say, 70 mph, putting the motor's entire RPM range within almost all daily driving conditions -- and then I wanted to do a cross-country trip on some roads with 85 mph limits? Would spinning the motors to 10,000 RPM or more be a problem if I was in all-V8 mode? But that would mean that the motors would be well past their optimum 5000 RPM on the freeway at 65 mph. For a car meant primarily for surface streets with little intention of freeway driving -- the typical urban subcompact, say -- that gearing would be ideal...but not for something in a sprawling Western metropolis where you can drive over 70 miles in a straight line on the freeway and still be in the same metropolitan area (Apache Junction to Buckeye). Again, in my case, the electric motors will be mostly powered down for that sort of extended freeway driving, but there're still plenty of shorter trips where the freeway makes sense for all-electric mode...and why spin the motors so fast for no good reason anyway? The next challenge for me is going to be to pick ideal gearing for the V8. Since the electric motors are going to have all kinds of torque from zero to 65, I'm thinking this is going to be a somewhat unusual situation for a daily driver where it'll make sense to optimize the V8 not for low-end torque but for high-end power and torque -- taller gearing than one would otherwise recommend. That's also going to carry over to decisions for the rebuild of the V8 itself -- heads, intake, exhaust, all that stuff. The more I think about it, the more I'm surprised that this type of hybrid isn't already popular in the racing world. Use electric motors for low-end torque, and ICE engines for high-end power, each optimized for its own part of the spectrum. b& -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 801 bytes Desc: Message signed with OpenPGP using GPGMail URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140805/8d66f4c9/attachment.pgp> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
