Does regenerative braking work above 90% charge?

Does regenerative braking work above 90% charge?

At this risk of Volker.Berlin pointing out that "this has been discussed extensively elsewhere..." (I searched and couldn't find it, really!)...

In this post ( Teoatawki talks about the car 'protecting itself' by not using regeneration when the battery is already charged, and Rod and Barbara suggest regeneration not working above 90%.

One of the things I really like about the Tesla is the regenerative braking. Many of my journeys will be relatively short and the car will be plugged in when it is at home, which means most of the time it will be >90% charged. Does that therefore mean I'll have no regenerative braking?

Or there will be regen braking but it doesn't charge the battery unless it is below 90%?

Confused of Boca Raton...

Brian H | 4 août 2012

Charging to above 90% should be rare, only done when you need the range for a long trip. That's "Range Mode". In Standard Mode, it will stop charging at 90%, and your regen will be unaffected.

Rod and Barbara | 4 août 2012

Just to be clear, when you charge in Standard mode the State Of Charge (SOC) of the battery at the end of the charge cycle will read 100%. However, the battery will only contain 90% of its max charge capability and regen will function normally. When you charge in Max Range mode the SOC of the battery at the end of the charge cycle will read 100% and regen will likely not work until the SOC drops to about 90%.

Michael23 | 4 août 2012

Strange, wouldn't they want to provide the regen feel so drivers have a consistent experiience when taking the foot off the accelerator? You could be driving and all the sudden it would change when you get to 90% too.

BYT | 4 août 2012

How about if the Model S lowers the volume of the radio for 3 seconds to allow for a soft female voice that say's, "Regen is now activated...ENJOY!"

nickjhowe | 4 août 2012

+1 Brian H and Rod and Barbara. Thx for the explanation.

Theresa | 4 août 2012

I am assuming the regen will work the same as the Roadster. It does not all of a sudden turn on. When you charge in range mode regen is non existent for the first several miles. As the state of charge gets lower the regen slowly increases until it gets to its normal operation.

In standard charge mode even though the battery is "fully" charged it is as Rod and Barbara state and the regen is fully functional.

SMOP | 4 août 2012


On all my Roadsters after a range mode charge, regen is disabled; after a few miles it comes on fully and normally. There is no "slow increase." Does your Roadster slowly increase regen after a range mode charge?

The REGEN being off is quite scary as the Roadster (at least) has very little rolling resistance. The roadster is relatively light, REGEN being disabled on a large 4600 lb sedan could be quite scary. I am sure Tesla could replicate the brake pedal feel of REGEN after a range mode charge without actively capturing energy.

Theresa | 4 août 2012


Yes on my Roadster (1.5) the regen slowly ramps up from a range mode charge. And I agree the first time that you don't have regen it is very scary. Once you realize it is going to happen you just plan for it. You still have brakes on the car.

As an example within about 4 miles I will start getting about 2 amps of recharge, As I get more miles on the car it slowly raises to 5,6,7,8, etc until it finally regens at the full rate. That rate of course is dependent upon the amount that you release the accelerator and the speed that you are going. I am fairly easy on the car as I try to get maximum mileage from every charge so the most I normally see is about 40 amps or regen. But I know I have had it over 100 amps when I first got the car and was having fun.

Teoatawki | 4 août 2012

Simulating regen when there's no room in the battery is problematic. Regen converts kinetic energy, which can neither be created or destroyed, into battery charge (and waste heat). So simulated regen converts kinetic energy into heat. So I suppose they could wire in a toaster heating element where excess energy is "burned off". Just seems like a really bad idea to me.

jkirkebo | 4 août 2012

The Leaf is the same. At 100% there is no regen. At 98% there is a little bit, and continually ramping up from there as the battery depletes. Full regen is not available until SOC is at 75-80% or thereabouts, depending also on temperature.

You quickly adapt to this, and there is no hazard. If you get no regen you quickly start braking instead. The brakes are so much more powerful than regen anyway so you have loads of margin.

Brian H | 4 août 2012

Yeah, simulated regen is almost nonsensical. Though I suppose the regen control s/w could use braking to "emulate" it in that range, without using the motor as a generator.

Might be a future role for ultra-caps?

jcadman22 | 4 août 2012

This variability on braking has got to be unnerving at the least and downright dangerous if you don't know about it. I saw at least a couple or three roadster owners use the word "scary" to describe this behavior. I don't know if that's something that I could get used to.

jkirkebo | 5 août 2012

I haven't driven a Roadster, but it's not at all scary in the Leaf. Also, the "regen circles" in the middle of the dashboard indicated how much regen is available. I am quite sure the Model S will have comparable instrumentation to indicate regen level available.

Brian H | 5 août 2012

Also becomes an issue if the battery is too chilled, until it warms. Not sure if the S allows that to happen.

Sparrow | 5 août 2012

Losing regen in the Leaf isn't scary because there isn't much regen when you let off the accelerator anyways, most of it is on the brake pedal. In the Roadster, there is enough regen that you don't really use the brake pedal to slow down thus when it is missing it might take a moment to realize, I have to push the brake pedal down or I won't slow down normally. It can be scary if you aren't thinking about it.

BYT | 5 août 2012

In the test drive event, the regen. felt very subtle to me! I don't feel the strong breaking in regen, like shifting from 2nd gear to 1st at 30 MPH, felt very subtle. Maybe I'm used to violent slowdowns based on my typical driving habits. My wife tends to get carsick a lot... :)

Brian H | 5 août 2012

Watching the testdrive vids, most people went through the full drive without touching the brakes except for the last 5 mph 'stopping' bits. Several of the passengers remarked or double-checked on that.

So, indeed it must be your violent driving. You're just naturally one of those "G-force addicts", I guess!

Brian H | 5 août 2012

Apparently it was the violence-prone like yourself at the first Fremont Amped event that caused the speed to be limited to 80mph for the rest of the drives.


BYT | 5 août 2012

GUILTY! :) I tend to ruin things for everyone, I'm sorry! I can't help it, I guess I really am a G-force addict? I actually think there should be a stronger selectable regen. setting. Much stronger! :)

Side Note: I test drove the standard but am buying the performance. I purposefully wanted to see the full potential of the car with less performance then what I was getting. I also would be very interested in taking my car out on the Tesla Motors track to open her up in a CHP free environment!

Volker.Berlin | 6 août 2012

nickjhowe, from the top of my head I cannot think of any thread where this has been explicitly discussed. Thank you for creating this thread! ;-)

I share the worries of the regen unexpectedly not working, to some degree. I think I would still hit the brakes quickly enough when this behavior gets me by surprise, but it is an accident waiting to happen. That's in my theory, and it does not help one bit that experienced Roadster drivers use the "s" word (the other one) to describe what they feel when this happens.

"Simulating regen" certainly does not mean to generate and waste electricity. It is surely a better idea to apply the regular disc brakes in this case (which, of course, end up converting kinetic energy into heat, anyway). The problem here, I suspect, is to precisely model the feel of the regenerative braking with friction brakes. If the braking is too strong, the surprise might be similarly dangerous as the regen unexpectedly not kicking in. I'm really not sure what the best solution to this problem is, but I do think it is a problem that needs attention.

Teoatawki | 6 août 2012

Actually, you have discussed this here.

gianni.terragni | 6 août 2012

I think is better and more symple "Simulating regen" generating and wasting electricity in a resistor than waste regular disc brakes, OF CORSE ONLY WHEN THE BATTERY IS OVER 90%.At the end we are always converting kinetik energy into heat but we don't downgrade the brakes and I think they can get the same risult they get with "real regen"

ItsNotAboutTheMoney | 6 août 2012

(I drive a Prius and very occasionally fill the battery to 8 bars and lose regen. The Prius, has an engine and that allows B mode to be used in this case.)

I think the biggest reason for not trying to simulate the same feel as regen braking is safety. When you've switched to the physical brakes you really need to know that you're using them because using the same braking has the potential to damage the brakes: you can comfortably regen down a long hill without concern other than filling the battery; if you ride the disk brakes down a long hill you risk overheating and damaging them.

Volker.Berlin | 6 août 2012

Teoatawki, indeed. Thanks for filling in! :-)

SMOP | 6 août 2012

Something else that Tesla could implement is charging based on location with respect to topography/traffic.

For example:

If I am doing a full range mode charge at my house (which is on top of a hill), the car could look at my location on a topo map and cross tab with potential REGEN captured from my location to the bottom of the hill. Or if I am doing a full range charge, it could cross tab with traffic in the area and only charge to x% taking into consideration a full REGEN supplemented range charge could be accomplished by the amount of energy while braking in heavy traffic etc. If something like this was implemented, then disabled REGEN would not be necessary. The goal should be for the brakes to act the same regardless of SOC

ggr | 6 août 2012

Having the regeneration disabled after a range charge is really not a problem in practice. There's a light on the dash reminding you that it's disabled, and the brakes work just fine. I don't understand all the fuss.

BYT | 6 août 2012

@SMOP, it maybe easier and better if the Model S learned your driving habits and adjusted the charge for Regen accordingly over time. Then maybe a way to reset it's cached memory if you move or travel to a vacation home for several months.

SMOP | 6 août 2012


Yea there is a cluster icon that has an X through the REGEN but some of us feel it is scary on the relatively light Roadster. I am sure it would be even scarier on the 4600lb Model S! Personally I would rather have the same brake/regen feel all the time rather than have REGEN disabled and retrain myself with regards to stopping distances. I have almost rear ended someone with REGEN disabled in the roadster.

FYI regen is also disabled when recalibrating the tires not just range mode

Teoatawki | 6 août 2012

This is the first time I've heard the phrase "recalibrating the tires." what is that and why?

SMOP | 6 août 2012


When you replace your tires you must re-calibrate the tires so that the traction control/speed readouts etc are accurate and work properly. There is a "New Tires" option where you have to drive in a line for 10 seconds with T/C turned off. REGEN is disabled during this calibration process.

jerry3 | 6 août 2012


You actually recalibrate the systems that tire revs per mile have an effect on to the new tires. The tires themselves don't get any calibration.

Brian H | 6 août 2012

Indeed. Tires are way too stupid to know from calibration, much less recalibration! ;)

SMOP | 6 août 2012

ok fine you guys got me with my nomenclature but you know what I meant ;) OT: you can retread tires...does this count as recalibration?

Brian H | 6 août 2012

No, but it probably throws off the speedometer/odometer. Or maybe it recorrects them if your tires were worn down:

Retreading starts with a safety inspection of the tire. The old tread is then buffed away, and a new rubber tread is applied to the bare "casing" using specialized machinery.

Retreads are significantly cheaper than new tires. As a result, they are widely used in large-scale operations such as trucking, busing and commercial aviation. They are also the most environmentally friendly way of recycling used tires - in some applications, a tire can be retreaded up to 10 times.

jerry3 | 7 août 2012


Ideally a tire's casing and the tread would have the same life, and this is true with car tires so retreading isn't viable.

With truck tires, in order to carry the load (4000 to 9000 lbs at 120 psi), you automatically have a casing that will last about 500,000 miles. Current tire technology can only make the tread last around 375,000 miles in the very best cases. It's usually more like 150,000 to 200,000 miles. So the typical highway truck tire can be retreaded once or twice.

Wikipedia sometimes pulls its information from out of... well, you know.

Brian H | 7 août 2012

Heh. With 21" stickies, some are suggesting about 10K lifespan for the treads. That would mean 15 - 20 retreads possible!

BYT | 7 août 2012

Retreading of tires end up littering the highways and roads. I hate this practice personally. We don't want to pollute the air with our cars, how about rubber on the streets?

Slindell | 7 août 2012

BYT: normal use of tires by everyone leaves far more rubber on the streets than the occational retread blow out.

jerry3 | 7 août 2012

About 80% of the material in a tire is in the casing and belts. Recycling tires is extremely expensive because the equipment is very expensive. You need something like 500,000 tires per day to make a tire recycling plant profitable. So getting the most tire life out of each casing is a worthwhile goal.

Brian H | 7 août 2012

So, the Tesla Retread Service is born!
Coming soon ...