Sustained regeneration performance - mountains and long steep hills?

Sustained regeneration performance - mountains and long steep hills?

I wonder how the Tesla S will perform on sustained downhills, like a down a mountain road. How much of the power used uphill will be regained?

I suspect the battery cooling in the Tesla S would help for sustained recharging. Driving in mountains, or places with lots of steep hills, this is quite important, and really where the EV is superior to fossil fuel vehicles (haven't yet heard of a car MAKING gas on a downhill ...)

How much can you brake and regenerate, before the disc brakes kick in? To me, the brakes on an EV should only be used for emergency stopping (and then every now and then, just to keep them alive and from corroding).

Thank you for your input

Teoatawki | 10 November, 2012

The battery pack can only store so much energy. Depending on the SOC, a long downgrade will allow regen, up to the limit of how fast the system can put energy back into the battery, and how much "room" is available in the pack. As the battery fills, the strength of the regenerative braking (controlled by the go pedal) will diminish, eventually to zero.

The brakes, on the other hand, are controlled by the brake pedal, and will need to be used when regen is insufficient. There is no crossover, that is, the disk brakes will never kick in for you.

I've found that in the Seattle area, most times both highway and city traffic are heavy enough that the brake pedal gets more use than I expected. I have only had the car a few days, but it is difficult to keep enough clear distance ahead to be able to rely nearly exclusively on regenerative braking. I hope I will gradually improve.

Brian H | 11 November, 2012

Yes, tailgating isn't well supported by regen! ;) Dense traffic, at least at moderate+ speeds, will be harder on brakes and range.

STEVEZ | 11 November, 2012

I've only had limited experience so far with long downhill runs in the S, but I can tell you that the rated range doesn't increase very much and thus neither does the battery SOC. The projected range goes through the roof (I saw 2463 miles at one point at the end of a long descent) but that's just a fluke of the algorithm and wishful thinking. Other posts have mentioned that the rated range/SOC numbers are only updated every three miles during descents, but I can't confirm that. The projected range is updated every few seconds.

What is absolutely wonderful is the way regen braking takes all the work out of driving downhill: you just set the cruise control and steer. I dropped about 3000' in 15 miles, on descending grades of up to 15% and with a couple of climbs thrown in, and I never had to touch the brake pedal or the accelerator. Of course, driving twisty mountain roads with the cruise control on limits the fun factor rather dramatically, but it's nice to know the capability is there.

sergiyz | 11 November, 2012

The max regen charge is at 60kw, and you have to be coasting at about 50mph to get to that level. The max output on P85 Perf is about 360kw, and with moderate acceleration you easily hit 80kw+.
Regen stops the car pretty, so I find myself keeping my foot on the accelerator most of the time even going downhill to maintain speed.
So, it may do you some good, but not a whole lot.

sergiyz | 11 November, 2012

...stops the car pretty fast that is, no way to correct your own post