Friday, March 30, 2012

The more things change, the more they stay the same.

So after wishing I could throw in the towel on this bb600 pack aftermultiple incidents of spewage, ground and interpack shorts that melted holes through a dozen cells, and apparent loss of capacity down to about 16 Ah, Karmann Eclectric didn't get a lot of use after a fall recommissioning of the pack, but I cycled it a few times over the winter, took a few short drives, and got the Onan range extending genset trailer working, due largely to a lack of confidence in the pack. The car seemed to be sulking, especially when I added a 2012 Mitsubishi iMiEV to the fleet! Well, it seems that the pack was actually ready for prime time once again! Tonight, with a pack temp of 50 deg and outside temps a few degrees lower, I topped off the charge and took the car for a diciplined 45 minute drive, covering a 27 mile loop with only 4 stops at intersections, for an average speed of 34.8 mph and a peak speed of 68 mph (climbed up and coasted down a 127 foot incline twice at speed, with many other smaller climbs). The 200 cell pack came off a peak charge of 333V and rested at 305V after about 15 minutes, with 0.1 Ah of parasitic consumption before takeoff. I set off with headlights blazing and pulled into the garage 45 minutes and 27 miles later, having consumed a total of 31.1 Ah, or 6.82 kwh. That's 1.148 Ah per mile, or at an estimated average V of 230, a battery-to-wheels efficiency figure of 264 Wh per mile. Next time I'll reset the EMeter to report kWh instead of Ah, and then it'll be time for some data collection with the range trailer hooked up!

Not bad, considering that this was at night in a car with a very heavy-duty transaxle and series motor, while my iMiEV consumed 257 Wh/mile during a 51 mile conservative daytime drive (though it's the current king of regen, that trip was mostly highway). Hey, guess it's time to hit the road again and drive that same loop in the i!

Back on the road, and the iMiEV made the same run in the same time with apparent consumption from the pack of 7 kwh. Sorry, the guessometer doesn't get any more accurate than the nearest kwh per bar on the graph. That would match the Ghia's performanceof 6.82 apparent kwh. (I minimized regen by shifting into neutral and coasting or braking as required to better match the Ghia driving style.)

So Mitsu, whassup with that? You produce the most efficient vehicle ever rated by EPA, and it's no better or maybe EVen a bit worse than a homebuilt drag racer cobbled together out of surplus and rebuilt castoffs and a heavy truck tranny? Time for more tests and better instrumentation!

Tuesday, March 27, 2012

To Make a Jelly Bean Fly.....

The iMiEV may look smooth, but with a Cd of 0.35,  it ain't exactly streamlined.  That round rear is not optimized for aerodynamic drag, and the slotted wheels aren't necessary when there's such little braking heat to dissipate, due to strong regenerative braking.  So, the DIY community has long cooked up little modifications like salt flat discs, fender skirts, air dams, belly pans, duckbills, rear visors, and even boat tails!  Here's a rendering of what some of those mods might look like on an i.  Here's also a link to a Dutchman who made the best DIY removeable boattail that I've seen. 
This quickie drawing shows what an iMiEV might look like with disc wheel covers, rear fender skirts, and two different options on the rear.  In black, I echoed the rear passenger window profile.  This could be done nicely in black lexan, and be semi-permanently affixed to the hatch.  A sharp rear edge would make better aero, but for the sake of buildability and artistic license, I chose a curve. 

In grey is the outline of a possible Kammback boat tail.  For you sailors, you'll recognize the concept of 'waterlining'.  Stretch out the same or even a bit more mass into a longer, more streamlined shape, and you'll reduce drag.  This one follows the rear body curves as closely as practical without actually touching, and has a sharp rear cutoff as dictated by good old Mr. Kamm

Here's a graphic of one of the few spoilers scientifically designed for drag reduction rather than downforce.  Too bad they're not commercially produced.  Time to start whittling!

And the Texas Mile winner in October 2011 chose a simple duckbill for drag reduction rather than a downforce spoiler.  If a high po Corvette doesn't lift at 245 mph, d'y'all rice boys really think that a wing's gonna help your Civic

So, the easiest among the above winners would be to simply add discs to the rims.  I went a notch up from JC Whitney's offering, but not quit Mooneyes pricing, and got the Taiwanese-made CCi brand, and am very pleased with the heavy gauge metal (yeah, adds a bit of rotating mass but doesn't dent when I push 'em on), excellent finishing, and positive lock on the wheel..  Still don't know how difficult they will be to remove, but I've got the right nylon pry tools. 
I'm thinkin it looks EVen better at night.