kert said:
Keeping the original engine for what ? My donor actually does not have
the running engine. Im ( initally ) keeping the gearbox for easier
transmission setup and mounting.
I dont think 600v DC bus is absolutely required,
http://www.metricmind.com/inverter.htm these for example are running on
400v. I might need to go with small SLA batteries instead still.
-kert
There is an ongoing discussion with lots of good (and some really bad)
information and ideas on the group:
http://groups.yahoo.com/group/SmallEfficientVehicles/
The motor should be at least 20 HP and probably 40 HP is ideal for a 3000
lb vehicle. I am a big fan of 3 phase induction motors, and I have rewound
a few motors for low voltage (about 8 VAC). You should probably get
something like an 1800 (4 pole) or 1200 (6 pole) RPM motor for more torque,
and you can V/F it for 2x or 3x. You will need a DC bus about 1.5 times the
motor VAC rating, so a 208/240 VAC motor would require less batteries (380
VDC), but that's still about 30 12 VDC batteries, and the high voltages are
a bit risky.
It would probably cost somewhere around $1000 to rewind a 20-40 HP motor
for lower voltage, and you may be able to get 2x, 3x, or even more HP by
using a V/F drive, and you might get by with a 10-15 HP motor. However, the
controller would need to be specially designed.
Another option is to use inverters to boost 12 VDC to 120 VAC and then
rectify that to get 180 VDC. I've seen 2000 Watt (3 HP) inverters at Harbor
Freight for $149. Four of these would give you 12 HP continuous, and a 720
VDC bus, which would be perfect for a 480 VAC V/F drive. You would need
some rather large capacitors for acceleration surges of a few seconds, or
maybe a second bank of much smaller batteries. A 5 second surge of 12000
watts is 60000 W-Sec. Regular capacitors are about 0.3 cubic inches per
Joule, and this capacitor pack would be about a 4 foot cube costing about
$15,000. Super capacitors are about 0.015 cubic inch per joule, so you
would have about a 1 foot cube costing about $8000. You could make a bank
of 200 3.6V 2 A-H Lithium Ion batteries for about $3200, or 60 7 A-H 12 V
SLA batteries for about $900. These would provide additional storage
capacity of 1400 W-H and 5000 W-H respectively. The main four 12 V 100 A-H
batteries would provide 4800 W-H. You probably use an average of about 5 HP
(7 kW) at highway speeds, so you will get about 1 hour running time without
regen, and maybe twice that if you can store the energy on downhills and
braking.
I know I have reversed my original idea of a special low voltage motor and
controller, but the high voltage inverter option uses standard components.
This will save the cost of motor rewinding and controller engineering. For
a production vehicle, however, I think the low voltage design will be
better.
For some quick figures on vehicle power, torque, acceleration, top speed,
etc., try my Excel spreadsheet at
www.smart.net/~pstech/VehiclePower.xls.
There is also a more sophisticated (but harder to use) on-line calculator
specifically or EV conversions. See the SEV newsgroup for the link.
Good luck!
Paul E. Schoen
