Regen limited due to cold today

[wycolo]

> The energy is in the system (your car) and needs to be dissipated somehow during braking. Currently, with limited regen, you heat up your brake discs, which are almost always up to the job. This suggests that the total amount of power we're talking about isn't vast. [Robert.Boston]

Either/Or would require a heavy (high voltage!) contactor. Not insignificant.

You could turn on HEAT full blast even before you leave home to possibly hasten return of REGEN. So if you live up-mountain it would minimize heat wasted to atmosphere by brakes.
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[Lloyd]

I left my Rav 4 EV outside last night to cold soak in the spirit of this thread. I only got about 50% of the normal amount of regen this am. 34 Degrees F with ice on the windows. I drove 15 miles and normal regen did not return, but it was hardly noticable. Toyota did a good job here!

 

[arg]

The energy is in the system (your car) and needs to be dissipated somehow during braking. Currently, with limited regen, you heat up your brake discs, which are almost always up to the job. This suggests that the total amount of power we're talking about isn't vast.

Well, we know exactly what the power is - up to 60kW. One saving grace is that it's not continuous - but could easily be 50% duty (drive max acceleration/max regen alternately).

In any case, a variant of my proposal is to make sure that existing systems to heat the cabin and the battery are fully used, providing more regen capability.

I don't think we know exactly what the ratings of those systems are, but it's unlikely to be more than 10kW total (I think I read 7kW for the cabin heat, but I am not sure of the source of that info). And heating the battery is only possible for the temperature-limited regen case [where I admit it would be extremely sensible to do!], not for the range-charge limited case. So it could move the regen limit a little bit, but not really solve the whole problem.

 

[eledille]

The energy is in the system (your car) and needs to be dissipated somehow during braking. Currently, with limited regen, you heat up your brake discs, which are almost always up to the job. This suggests that the total amount of power we're talking about isn't vast.

Even if the total energy isn't large, it comes in powerful bursts, which complicates the task of putting it to good use.

In any case, a variant of my proposal is to make sure that existing systems to heat the cabin and the battery are fully used, providing more regen capability.

Using the regenerated energy to warm the battery seems like a good idea to me. It just might be doable too - a heater immersed in the coolant should be able to absorb enough power to provide some regen.

Model S has the capability to warm the battery coolant already, doesn't it? If so, it shouldn't be all that expensive to increase the size of the existing equipment a bit.

 

[jerry33]

I always think it's curious when people in mild climates like Vancouver and Halifax refer to "black ice", because I've never seen black ice under those conditions. Must be some other differences in the climate.

The black ice we get here happens when its -20C or colder and windy enough to blow around dry snow. The previously completely dry road - no snowfall is required for this - gradually and incrementally accumulates a ridiculously thin layer of ice. Passing vehicles actually help polish it up nicely. Once it's formed the only clue that it's there is that the road looks a little blacker than normal. If you're not watching out for it you suddenly discover that you have no traction whatsoever. The stuff is incredibly slick.

In Vancouver, the rain can freeze on the road and it looks no different than the wet pavement. Other than black ice, I don't know what you'd call it. It's always very slick because there is a film of water on top of it--and yes, you have no traction.

 

[brianman]

For those with a panoramic roof, it could be opened 1% and excess heat vented out.

 

[Slackjaw]

The first time my Roadster turned off Regen due to cold (and I mean completely OFF), I didn't notice the light on the console. There's a yellow REGEN with X through it light. I didn't notice it because whenever it's cold you get that stupid "ICY" symbol lit up yellow (hate those things - like I don't already know it's cold???), so with a quick glance I didn't notice anything out of the ordinary.

Anyway, completely unaware I drove to the parking lot exit, took my foot of the pedal, and HOLY CRAP the car is rolling! It was so frictionless, and so different a feel, that it almost seemed like it was taking off on me. Naturally I immediately hit the brakes, and a split second later I realized what happened and looked at the console to confirm.

So for a novice user, it would probably be a good idea to have a more "vocal" warning if the regen is lowered by more than half. But that's a feature I'd really want to turn off once I was used to the car.

Exactly the same happened to me yesterday - Roadster was outside at work at around 17F or ~ -8C and had zero regen when I took off. A first for me - although I'm hardly a novice drive in this car (got 27K miles on it), this is the first really cold weather we've had since we got this car. After the first stop light I tuned my driving and won't be caught out again, but a more aggressive warning would have been nice. I've done a few range mode charges (maybe five) but that's different just because you have all those other warnings about range mode etc., and you're expecting something. So +1 to what Doug said...