Steve Heath via EV wrote:
I'm not sure that I understand what the further complications are. As far as I can see, it should be just simple math. The energy use measured at the motor should be the same as the energy consumed at the battery, minus some percentage for losses in the controller, which will vary with conditions, but can be averaged. Am I missing something?
Not really but there are other factors that come into play such as battery recovery time, regen and so on. It makes these losses very difficult to calculate as they are non-linear and condition dependent. Averaging is better than nothing.
Yes, it's better than ignoring them. However, most of these losses are non-linear. For example, resistive losses in the motor, batteries, and wiring go up as the square of the current; not linearly. Controller and charger efficiency are highly non-linear as well. The batteries have something called the Peukert effect, which means their apparent amphour capacity goes down as current rises.
The level of effect is also dependent on how much leeway you have in your vehicle. To me it is very important as I have a small battery pack - it is now around 6-7kw - and saving 10 or 20 watts per mile can make a big difference.
I agree. For most of the history of EVs, our battery packs have always been "small" compared to a tank of gasoline. It has forced EV'ers to think about efficiency.
All this is all to do with removing/reducing range anxiety. Matters are not helped when power consumption doubles when the heater is on. Why manufacturers don't have a separate battery pack for the ancillaries so that their use does not reduce the driving range, I don't know. Presumably it is cost and the amount of power needed to power all the gizmos that marketing insist must be present. Anyway getting away from the original topic.
It makes more sense to have one big battery than two smaller ones, only one of which is used to propel the car. Range inevitably drops when the heater or A/C is used. But that's true for ICEs as well (though not so much for the heater; ICE's have more heat than they know what to do with).
On the amount of power cars use: We go out of our way to have efficient home heating and cooling systems. We have portable clocks, computers, and radios that use tiny amounts of power. But cars (including EVs) are still designed for the "oil age" when power is infinite and free.
It takes more power to heat or cool a car than an entire apartment. Cars have negligible insulation, lots of air leaks, and are all single-pane windows. Most of the lights are still tungsten bulbs. A car's clock, radio, and computers use 100's of times more power than your other battery-operated clocks, radios, or computers. The automakers have simply not had to think about power.
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