A better way to measure the efficiency of the battery discharge, separate from the losses in the inverter/motor, is to monitor the battery voltage drop under load with the gid meter.edatoakrun said:Herm said:garygid said:GIDs might be 80 Wh into the battery, but you do not recover
the full 80 FROM the battery.
Since we drive with the recovered energy, not what was put in,
the "usable" 75 Wh per GID accounts for that loss.
Supposedly GIDs are WHAT IS STORED in the battery, it took a bit more than that to fill those batteries but we dont care about that.. extracting those kWh out of the battery wont be 100 percent efficient, especially if you drive aggressively.. but 75 sounds like a reasonable number with motor/inverter, tires and gearing losses. The battery itself will be close to 100% efficient while discharging, otherwise it would get very hot.
I doubt it.
Just by watching the battery temperature bars while driving, I'd expect the discharge efficiency will be found to be somewhere in the mid 90's percent, once it is accurately calculated. Both the 80/75 gid count and Carwings available battery capacity reports, as compared to Phil's calculations of total battery capacity, point to this eventual conclusion.
95% discharge efficiency would mean about 1 kWh was released as heat over a full LEAF battery pack discharge cycle.
The battery does not get "very hot", since that's not very much heat, given the thermal mass of a 600 lb battery pack, which is constantly being passively cooled, while you drive.
Data collection procedure:
record idle voltage with car at rest or in neutral.
operate car at uniform power level, 10, 20, 30, 40 kW
record voltage at each power level
return car to stop or neutral, and record idle voltage again.
Since I do not have the data-logger port (nor a lap-top to connect it to), it is difficult for me to get precise readings while driving, but here are my rough results:
Power Voltage Drop
10kW 4V
20kW 5-6V
30kW 8-11V
40kW 13-15V
(voltage drop)/(idle voltage) = the fraction of power lost in battery discharge.
The pack voltage was about 375 volts, so under most cruising conditions, where power is no more than 30 kW, battery discharge loss is no more than 3%.