What's more efficient - coasting or regen?

[Sesamecrunch]

Is there scientific or conventional wisdom about whether it's more energy efficient to coast or to use battery regen in normal driving?

For example, if you're on a slight downhill stretch of road, is it more efficient to put the car in neutral, or in L mode?

My bet is on coasting. There's no loss of energy in converting kinetic energy to electric. Sure, you don't get to charge the battery, but you're rolling a lot further without consuming any energy.

What do you think? What do y'all normally do?

 

[ecilopaveht]

Is there scientific or conventional wisdom about whether it's more energy efficient to coast or to use battery regen in normal driving?

For example, if you're on a slight downhill stretch of road, is it more efficient to put the car in neutral, or in L mode?

My bet is on coasting. There's no loss of energy in converting kinetic energy to electric. Sure, you don't get to charge the battery, but you're rolling a lot further without consuming any energy.

What do you think? What do y'all normally do?

There would be many variables to this question to properly answer it. It would be situation specific. For example I have a hill that I drive down everyday on my way to work. about a 6% grade for 2 miles, at the bottom there is a tunnel and traffic always slows to a crawl. If I coasted down the hill and just used L at the last min to stop I would only get a quick high power charge, but If I used D all the way down I get a constant 11 KW for 2 miles this charges my battery a few extra miles. Now one could assume that if you had perfect conditions with a good grade, straight road and level ground at the bottom you may be able to coast farther then the energy gained from regen, but I think regen is better. I am definitely no scientist, this is just my opinion based on my observations.

 

[rbroders]

I guess the first question is how does our transmission work. Since motors can operate forwards and backwards and have very little friction when being backdriven, there is really no need for F, R or Neutral. Just a single gearing locked in place is all that is required.

I'm pretty sure Chevy just used the normal Spark transmission after throwing away most of the gears. Do we still have a true F, R and N?

If you are in true N, the regen braking system will be disabled and if you touch the brakes at all you will be wasting energy.

If you can go down the hill without needing brakes or power then I suppose there would be a tiny mileage improvement from using N (because it doesn't spin the motor and a few of the gears in the gearbox). The friction of these things are quite negligible though and I doubt you could measure the difference...

If you are talking about using the regen system to modify your speed then it is a different story and generally slower is better as far as mileage is concerned...

--Bob

 

[REB]

This has been discussed a number of times at the Chevy Volt site with the basic physics answer that you will always loose a percentage of energy due to frictional losses going one form of energy, kinetic (motion) to electric to battery back to electric to the motor and back to the energy of motion.

A road situation with no interfering traffic would be most efficient coasting rather then any regen but since that doesn't happen very often the variables come into play.

It is still debated but I'm of the opinion that L in the Volt and Spark would garner the most regen.

Having someone on your bumper might require D however so you minimize your chance at getting rear ended with regen.

Ross

 

[kevin]

...

Having someone on your bumper might require D however so you minimize your chance at getting rear ended with regen.

Ross

Don't forget that you can control how much regeneration (and how much the car slows) with the accelerator pedal. The power indication on the dashboard shows how much regeneration you are getting. If you control the power to indicate zero you are effectively coasting.

kevin