Optimum regenerative braking

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bryand

Member
Joined
Jul 22, 2014
Messages
24
Location
Loughborough, UK
If I'm driving an i3 down a long steep hill, what's the best strategy for getting the maximum charge into the battery by the time I get to the bottom? Should I drive slowly to maximise the amount of time regenerative braking is working, or quickly to spin the system up more, but for less time?
I suspect the theoretical and actual answers will be different.
Any ideas/experiences from i3 drivers?
 
Coast...but if that causes the vehicle to speed up, release the pedal a bit to add in some regen. IOW, keep the indicator exactly in the middle or in regen going down the hill. The cruise control does a very good job of this, probably better than you can do, unless the slope varies a lot.
 
Going the speed limit (or whatever your choice is) both up and downhill is a personal decision. But, the point is, with the i3, there are three modes: using energy, coasting, or regeneration...and, you control this with the pedal. If you want to go faster, push it, using gravity is the cheapest use in energy to keep going, if coasting gets you going faster than you want, back off from coasting to start some regen, slow down, push a little harder. Regen is never going to be as efficient as coasting...there's a conversion loss...so, not using any while still moving is always going to be the smallest energy user.
 
Theoretically, going fast and having aerodynamic drag eat away more potential regen energy would be less optimal than maintaining a slower, longer regeneration.

Theoretically, a slower, longer regen would take longer and cause greater parasite draws from your heating/cooling, operating, and entertainment systems.

In reality, any difference would be imperceptible. Just drive the car. That's how its designed.
 
I live near Henley-on-Thames and to get into the town you go down a pretty steep hill a mile or so long with a 40mph limit. The cruise control on my BEV is easily capable of holding a fully occupied car at that speed and the regeneration typically adds 2 miles to the indicated range by the time I get to the bottom. Which is nice.

I find the cruise control is much better than me at maintains speed and optimal power consumption, on the i3 or an ICE car.
 
DerfSdrawd"regeneration typically adds 2 miles to the indicated range by the time I get to the bottom. Which is nice.[/quote said:
Although the regeneration will add to the range it's likely that the range estimation is looking at your recent history (going downhill) and using that in it's prediction. You may well get more or less the same increase by coasting down - provided you don't mind exceeding the speed limit!
Click to expand...
 
BrianStanier said:
DerfSdrawd"regeneration typically adds 2 miles to the indicated range by the time I get to the bottom. Which is nice. Although the regeneration will add to the range it's likely that the range estimation is looking at your recent history (going downhill) and using that in it's prediction. You may well get more or less the same increase by coasting down - provided you don't mind exceeding the speed limit![/quote said:
I'm going to try it! Although I'll be doing about 75mph at the bottom.... but then instead of using the energy of the car to charge the battery I'm just letting it go free by allowing the car to speed up, and turning it into heat when I hit the brakes on to avoid the bend.
Click to expand...
Click to expand...
 
DerfSdrawd said:
I'm going to try it! Although I'll be doing about 75mph at the bottom.... but then instead of using the energy of the car to charge the battery I'm just letting it go free by allowing the car to speed up, and turning it into heat when I hit the brakes on to avoid the bend.
Click to expand...
Coasting is usually most efficient, so long as it is not followed by brakes or accelerating. Any amount of regen that avoids additional braking OR additional acceleration than what would be used if you coasted instead will be better than coasting. When going down hill, coast only if you can use the resultant speed at the bottom, and use regen otherwise.

The optimum amount of regen is that which leaves you at the maximum usable speed following the regen. That is true for descending or climbing a hill, or just needing to slow down or approaching a stop (ending with zero speed).
 

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