Using Ev Mode

[BlueValour]

I have been adopting the practice of driving up and down my cul-de-sac in EV mode to save fuel, switching to normal mode only when on the main road. It will do a return trip by the time the Battery reaches the red. Is this sensible or might it be causing other problems?

[Grumpy Cabbie]

Hmmm occasional use is ok but you don't really want to be running the Battery up and down deliberately too much - esp to extremes.

Just let the car sort itself out. It is tempting to impress with EV though, but just not to run it right down.

[timberwolf]

How do you know that your EV mode strategy is saving fuel?

The energy stored in the HV Battery has to come from burning fossil fuel. Even when you use regenerative braking, it can only capture back some of the energy that has previously come from some of the energy originally stored in the fossil fuel. There are also the losses from storing and then converting back the energy from the HV Battery into motion e.g. fuel -> petrol engine -> mechanical -> electrical -> chemical then back again Battery -> chemical -> electrical -> mechanical. Each of the steps involves losses otherwise I think we would have perpetual motion.

I can think of a simple example where it is easy to see that EV mode makes sense, moving the car a very short distance e.g. moving the car off a drive way but you don't want to start the petrol engine just to run it for such a short period.

You've also got to factor in the warm up time of the petrol engine and a little quirk of the Gen 2, i.e. whether your journey has a stop to allow the Prius Gen 2 to reach the most efficient stage of operation (see http://www.techno-fandom.org/~hobbit/cars/five-stages.txt).

Personally, I don't bother with EV mode in regular driving and I think my limited driving time is better spent on trying to drive smoothly and using the brakes as little as possible - my objective is to try to use the HV battery as little as possible and if I can keep it between 50-60% for the whole journey then I think I've done well.