Lots of experimenting

No pictures today, but a few interesting insights from the first few runs around the block.

Living on a fairly steep hill, we have been testing quite a bit going up the hill and then coasting back down.  Not wanting to get stranded at the bottom of the hill entering the neighborhood, it is critical that Jane can make it back home.  So far, it powers right up the 150 yard hill with little hesitation.  Still limited to about 1,200 RPM due to the lead-acid batteries being used for testing.  Three decent used batteries in series is holding  steady at 34-35 volts under load.  The Kelly controller provides a ammeter signal for an analog meter that reads as a percent of "controller maximum motor current".  The car climbs the hill at about 280 amps (40% of 700 amps maximum)  at the motor.  The motor is rates at 125A continuous and 450A maximum for 1 minute, so this seems within the reasonable range for 45 second hill climb.  We did 4 climbs yesterday before the batteries started to dip.  The motor was warm to the touch, but not hot.  The motor's operating max winding temperature is 145C and has a thermistor connected to the controller which should shut things down if it gets close to this temperature.  On a minor uphill grade, the motor is pulling about 140A at maximum RPM.  There are no flat roads in the neighborhood, so until we have enough confidence that Jane can make it home, hill testing is all that is available.

Power Booster

The Kelly controller is recommended to run above 18V, isolated from the main batteries.  The standard starting battery is still in the car to power the electronics (radio, lights, blinkers) but only provides ~12V.  Amazon sells a voltage booster based on the TI LM2577 Link for about $9.  This worked great and now the controller is powered right at 25V.  There are numerous comments that the higher supply voltage enables the controller to operate better, but I am not sure exactly how.

Battery Selection

The search and calculations continue regarding battery choice.  The CALB CA60FI are leading the pack.  They can provide 10C which means a pack will be able to supply 600A for 30-60 seconds.  The motors 1 minute maximum rating is 600A into the controller, so this seems like a good match.  Also, the CALB packs are carried by a number of resellers which adds to their credibility.  The remaining questions revolves around the total target voltage for the battery system.  The default choice is 77V (nominal) which would be 24 packs a 3.2V each.  However, every volt yields about 50 additional RPM so a 84V system will allow the motor to generate additional 350 RPM which in 3rd gear equates to about an additional 5 MPH.  Not a big deal but could mean the different between 35 mph and 40 mph, which even for city driving would be nice.  In 4th gear, it is almost a 7 mph difference.  Now pushing the limits up to 90V (2 more packs) will yield yet another 300 additional rpm and few more mph.  With the lower gearing, it may not be too big of deal.  Putting the full battery system into service at the same time enables the packs to age equally and that should help maintain balance.

A few more experiments this weekend and then it will be time to decide.