Tuesday, January 19, 2016

Stuffing the KurbWatt

The original Grumman battery tray will hold 11 Group 27 batteries after removing some of the center partitions Yes, that weakens it somewhat, but in the long and strong direction, but we reinforced the floor and have reduced battery weight by over one third.  We've also found another battery donor, one of the few local users of Valence batteries, for a total of 24 U-Charge XP27 batteries available, which adds up to 39.9 kWh!   This would give the truck a 39.9 kWh pack weighing only 1056 lbs.

 Three batteries will fit in an unused body cavities ahead of the rear wheels on the passenger side, but only two behind the driver due to cable routing.  The seat platforms are nice boxes that will also hold two batteries apiece.

 Add up to five batteries in the motor compartment, and the count stands at 24.   That should be good for up to 200 miles at low speed around town, or no less than 114 miles on the highway!

Battery placement is still being decided, and we may use fewer batteries to KISS, but we also have two Valence U-Charge BMS systems, each originally set up for 12 batteries.  Running two packs in parallel would extract the maximum energy at minimum stress, while operating at safer voltages (144V nominal rather than 288V).  Power delivered by the controller would be greater at 288V, because then the motor could be fed with 170V, which the maximum voltage for decent brush life, and not sag below that 170V during high current (1000 amp) accelerations.  That 170 kW would be 240 instantaneous horsepower, probably more than the Rabbit clutch could tolerate!

144V or EVen 132V is our likely course since students are involved, but it leaves an option open for putting the sub-packs in series when daddy goes to the track!



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