A while back, I was taking power use measurements of the Citicar at various speeds.
See thread: http://ecomodder.com/forum/showthrea...ease-1307.html
In order to get to top speed – a whopping 37 MPH – I use Field Weakening. At 37 MPH, it uses about 35 more amps than at 34 MPH (non-FW top speed). Part of the graph hinted that in certain conditions, FW might be more efficient than non-FW.
A couple of days ago, I started a new experiment with the Citicar to see if Field Weakening could be used to increase efficiency.
For reference, Field Weakening basically shunts part of the current away from the field section of the electric motor, reducing back-EMF. I use a 6” piece of ½” wide Nichrome wire as the field shunt, switched in with a solenoid.
New controller mount layout
The picture above shows the Alltrax 7245 mounted to the heat sink. The Field Weakening resistor is the curled Nicrome wire mounted on two ceramic posts at the lower right. Albright SW-202 F/R contactor mounted at top right, with Kilovac main contactor (white can on left under F/R) and weakening contactor (silver can at lower right behind weakening resistor).
In previous experiments, I determined that FW increases acceleration in my vehicle at speeds above about 2,200 RPM (roughly 19 MPH in the Citicar). For the test, I turn on FW by letting off the accelerator (turns off controller) switching on the FW contactor, and then resuming speed. I do this once I am above 25 MPH, and keep the speed around 25 MPH. The speed limit is 25 MPH on most roads in Alameda. In practice, FW is on between 19 and 30 MPH for roughly half of the trip.
Before the test, my average power use was about 230 wH/mi without the use of FW. Here are some preliminary results using FW–
Day 1 – 11.9 mi – 224 wH/mi
Day 2 – 13.9 mi – 217 wH/mi
Day 3 – 11.3 mi – 232 wH/mi
Day 4 – 23.0 mi – 227 wH/mi
Day 5 – 15.0 mi – 220 wH/mi
Day 6 – 14.1 mi – 194 wH/mi
Average for 19.55 kWh / 89.2 miles is 219 wH/mi, or about a 5% gain in efficiency. I measure kWh used at the wall plug, so the total power use includes battery charger losses, etc. I plan on continuing this test for about 30 trips to get a good average power use.