Author Topic: Hypermiling in electric cars  (Read 4371 times)

igthebold

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Hypermiling in electric cars
« on: September 13, 2012, 06:45:39 AM »
I'm idly curious.. what does hypermiling look like in electric cars? Efficiency is in the form of miles per kWh, I assume.

  • Pulse and glide requires.. letting off the accelerator? Is there a neutral gear in electric cars? I guess there at least needs to be a free-wheel or something so it can coast.
  • No energy usage other than for instruments when sitting at a stoplight.
  • All the factors unrelated to the engine are still in play: drafting, fast corners, rolling stops, timing lights, don't use brakes if possible
  • What about acceleration? Fast acceleration is inefficient with an ICE.. what about with an electric motor?

Seems like a hypermiler's dream.

MrSaturday

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Re: Hypermiling in electric cars
« Reply #1 on: September 13, 2012, 09:11:24 AM »
Electric motors are most efficient at low rpm, and braking generates power.

That doesn't necessarily mean it's a good idea to do a lot of starts and stops, but it won't cause the big losses you'd see in an ICE.

Jamesqf

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Re: Hypermiling in electric cars
« Reply #2 on: September 13, 2012, 01:42:04 PM »
Pulse & glide shouldn't have much effect with an electric.  The theory there is that with an IC engine, the pulse portion runs the engine at its most efficient BSFC point.  That doesn't apply to electric at all.  Likewise, there shouldn't be much of a penalty for fast acceleration, for the same reason.  (This is even true to some extent in a hybrid: I use less gas if I accelerate briskly enough for the electric assist to kick in.)

HumanAfterAll

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Re: Hypermiling in electric cars
« Reply #3 on: September 13, 2012, 02:53:06 PM »
Accessories like the heater directly consume battery power, unlike conventional cars which use waste heat from the cooling system.  So, use blankets in winter!  (I already do this in my conventional car, until it warms up.  $2.99 fleece blankets from Rite Aid)

Slow down gradually to take full advantage of regenerative braking.

Accelerating fast or slow, as well as pulse & glide, should have no effect.

Keep speeds low - aerodynamic drag still goes up with speed squared, but most electric cars have better aerodynamics than conventional cars. 

Choose routes that allow you to travel at a lower speed without stopping as much, just like you would in a conventional car.

Posthumane

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Re: Hypermiling in electric cars
« Reply #4 on: September 13, 2012, 03:21:58 PM »
Electric motors do not have a flat efficiency curve across their rpm range. There is a peak efficiency point, just like in an ICE, though the efficiency curve is generally a bit flatter. Both at no load and at stall the efficiency drops to zero. If the peak efficiency point is not matched to the power required for steady state driving, which it can't be for all conditions, then pulse and glide could certainly have some benefit with electric motors as well. Likewise, overly rapid (or overly slow) acceleration will reduce the efficiency of the motor, so there are some savings to be had be driving diligently and being aware of the motor's properties, just as with an ICE. Regenerative braking only scavenges a small percentage of the kinetic energy of the vehicle, so looking ahead and choosing your speed and following distance to reduce the use of brakes still helps.