Not enough regen braking

[destructure00]

This time of year in Phoenix the overnight lows are in the 30s and low 40s. I garage my car, garage temp in the morning is 60-65. I typically charge to 90% each night, but recently had issues with not having full regen until I dropped into the high 70s SOC (which is halfway home in the afternoon in my daily round trip to work). Set my charge limit to 75% instead of 90 and now have full regen first thing in the morning. Will turn it back up once it starts to warm up again.

 

[Feathermerchan]

I have 'Scanmytesla' and have seen limited regen with the bat temp 57 deg F.
Preheating the interior of the car does little to warm the battery. Driving does more.
Remember that you do not get all the energy back when you regen. Probably only about 70% so unless you lose all regen and do a lot of stop and go driving, it won't affect range much.
It seems most people here are making comments because they have lost the ability to drive with only one pedal. Is that lazy?

 

[Candleflame]

this is all BS. I'm in hot climate and I dont have regen either. certainly not enough for the car to slow down enough with regen alone. I have to constantly brake now.

 

[TydalForce]

today regen was hardly working. so sad....

can they make the motor do braking without regen?
I just like one pedal driving so much..

Agreed; I wish they would.

It seems most people here are making comments because they have lost the ability to drive with only one pedal. Is that lazy?

It's not lazy, it's a combination of preference and a lack of consistency in the car - it's changing the way it behaves, changing the actions you need to take. It's disorienting, and sometimes comes as a surprise.

 

[Feathermerchan]

Surprising and disorienting. Like hitting a patch of ice. Similarly, the Lithium Ion battery is damaged by charging too fast when cold or near full charge so regen must be limited. Maybe someday, the car can utilize the brakes when regen is limited/unavailable.

 

[SlimJim]

Surprising and disorienting. Like hitting a patch of ice. Similarly, the Lithium Ion battery is damaged by charging too fast when cold or near full charge so regen must be limited. Maybe someday, the car can utilize the brakes when regen is limited/unavailable.

Or have the electricity bypass the battery if recharge is not recommended.
Make the extra regen go to heating element to warm up the cold batteries instead or something.

 

[Feathermerchan]

It's the or something. The energy has to go somewhere. Brakes are designed for this purpose.

 

[MountainRatMat]

Or have the electricity bypass the battery if recharge is not recommended.
Make the extra regen go to heating element to warm up the cold batteries instead or something.

I'll admit I'm not an expert here but I would speculate that would require extra hardware. The amount of energy dissipated would be too much for the existing heating element. Maybe a future cold weather package idea with an extra resistive heating element inside the battery for this exact purpose.

 

[SlimJim]

I'll admit I'm not an expert here but I would speculate that would require extra hardware. The amount of energy dissipated would be too much for the existing heating element. Maybe a future cold weather package idea with an extra resistive heating element inside the battery for this exact purpose.

In future models, they could also utilize moving spoilers to create extra drag when regen is turned down.


" the kinetic energy of a slowly moving car is low enough that very little energy is put back into the battery as the car comes to a stop. In fact, the last little bit of slowing the vehicle down generates such a small amount of energy that it does not even cover the fixed losses in the inverter and motor."

Therefore, in crawling traffic or near coming to a stop, regen braking wouldn't hurt the battery because regen amount is so little.

 

[MountainRatMat]

In future models, they could also utilize moving spoilers to create extra drag when regen is turned down.

Tesla tried this and ditched it already, the X used to have a moving spoiler but no longer does.

 

[Yang_H]

Or have the electricity bypass the battery if recharge is not recommended.
Make the extra regen go to heating element to warm up the cold batteries instead or something.

I always thought this a logical and brilliant idea. When battery is too cold to regen you direct regen to heat the battery. It might require some extra design and hardware, but it makes perfect sense in every way.

 

[Feathermerchan]

I think warm battery regen is limited to 60kW. That's about 80HP. 80HP of drag is like a parachute not a spoiler.
Brakes are designed for this and are already electrically operated so it will just take software.

 

[Fredneck]

Surprising and disorienting. Like hitting a patch of ice. Similarly, the Lithium Ion battery is damaged by charging too fast when cold or near full charge so regen must be limited. Maybe someday, the car can utilize the brakes when regen is limited/unavailable.

If they put some effort into the issue, they could dissipate the heat in the motor in a similar manner to what they do to heat the battery while the car is stopped. My X has electric heaters, but the 3 uses the motor. They put tons of effort into making the motors more efficient. They should also be able to make them dissipate extra heat when desired.

 

[Fredneck]

I always thought this a logical and brilliant idea. When battery is too cold to regen you direct regen to heat the battery. It might require some extra design and hardware, but it makes perfect sense in every way.

It may be practical if they do the heating directly in the motors. It's just that the system is designed to deal with some heat in the motors, but not 60 kW I don't think.

 

[Feathermerchan]

And it's probably more than 60kW. If a motor is 300 kW and 90% efficient, then it needs 30 kW of cooling max. So making it dissipate 60kW and expecting it to survive is unrealistic.

Using the motor to slow the car down is limited on RWD models and even on the AWD models I'm not sure they use the front motor for regen.

 

[Fredneck]

And it's probably more than 60kW. If a motor is 300 kW and 90% efficient, then it needs 30 kW of cooling max. So making it dissipate 60kW and expecting it to survive is unrealistic.

Using the motor to slow the car down is limited on RWD models and even on the AWD models I'm not sure they use the front motor for regen.

I wouldn't assume 10% losses in the motor. I think it is lower than that. Even so, a motor has a large thermal mass. It can take more power for a short time such as slowing a car. Just like accelerating a car is a transitory event, so the motor isn't going to be designed to get rid of the waste heat for a long period of acceleration. I know in the model S running the speed up and down will result in a power reduction for thermal reasons. I don't know much about the 3 in the same regard.

 

[Feathermerchan]

So do you want to lose regen because the motor is overheating?

OK so a 300kW motor at 95% efficiency has 15kW of losses. The cooling system is designed around 15kW. Now you have even less regen capability. Brakes are designed to stop the car. Use they should be used for that purpose. By the driver or by the software.

Overall remember that the best efficiency is no regen at all. Coast unless not practical. It will make a measurable difference in your efficiency and you will not notice the loss of regen as much.

 

[Yang_H]

I agree with the saying that regen is not just for energy efficiency, it's more about consistency of driving. Once got used to one pedal driving, it just feels uneasy if not dangerous to drive without regen. So it'll be great if they can find way to help cars maintain the same regen in cold temperature.

 

[Daniel in SD]

Tesla definitely dialed back the regen this year. Been getting down to 50F at night here and some mornings I get almost no regen at 80% charge. It starts off with only a few dots but after a couple hundred feet of downhill it's time to use the brakes. I guess they're having trouble fighting off those dendrites! I just hope I don't lose supercharging in the future...

 

[Big Earl]

I always thought this a logical and brilliant idea. When battery is too cold to regen you direct regen to heat the battery. It might require some extra design and hardware, but it makes perfect sense in every way.

It already does this. The battery’s cooling/heating system and only dissipate so much heat before it gets overwhelmed (let’s say about 7 kW). Full regen is about 60 kW. There is no way to safely dump 60 kW of heat directly into the battery pack, let alone for a period of more than a few seconds.