Regen limited due to cold today

[Doug_G]

I don't think it is that bad: after all, the amount of heat is exactly the same as the heat to be dissipated in the friction brakes if regen is disabled. So a resistance heater in the wheel-well (cooled by the air after it has passed through the radiators) would leave the heat distribution exactly as it is now.

Except that resistors can't tolerate the temperature levels that a slab of steel can. The brake rotors on your car get quite hot.

 

[KBF]

Ha Ha, yes we Ontarians don't have Winnipeg's superior infrastructure. But seriously, don't block heater outlets limit power and/or cycle on and off to balance load and/or only work below certain temperatures? I wonder if they would, or even could be used for EV charging?

Yes, most block heater outlets in a public parking lot (from what my electrical company father-in-law says) have two separate circuits that alternate so that a specific plug is on about half the time. They are on long enough, though, that a car can heat up properly and avoid being cold-soaked, so I would be surprised if there was an issue. Of course, looking at the above conversation, it appears as though the Model S may not be any different plugged in vs not (WRT battery temp control), so the only benefit is offsetting the battery loss. As far as charging in a parking lot, it's not like it's attached to a cheap generator, it's all grid-tied, just not on half the time.

I see the cold situation as resolving itself once Tesla gets their "custom timer" software going; I would hope that not only will it charge according to one's scheduled departure, but also heat the battery enough that the regen isn't an issue. If it is programmable we will not waste electrons keeping things toasty warm.

*edit: also, AFAIK, some cheap parking lot owners may turn off the hydro from April-November. But since we're likely only worried about offsetting what is used to heat up the car, it's a non-issue. If the government wanted to promote electric car use, they could mandate changes to the way it works now; the infrastructure is there, some might need to be upgraded, and the amperage would be low, but it exists.

At work, my boss is happy to let me plug in to a regular socket so it's no problem.

 

[arg]

Except that resistors can't tolerate the temperature levels that a slab of steel can. The brake rotors on your car get quite hot.

Well, resistors sold as precision resistors might not, but resistors for this sort of application are more like heating elements and certainly could run to similar temperatures to a brake disk. here are some resistors rated up to 100kW - the resistance material is in fact a steel alloy, though unlike the brake disk it doesn't have to have much mechanical strength when it is at operating temperature. Apparently these ones are designed to an NMEA standard for industrial controlgear, limiting the temperature rise to 375C above ambient, so not quite up to brake disk levels but not far off.

However, an example from that site quotes 60kg weight for a 25kW device (including its protective cage), so that isn't a practical solution. You could probably do better with something designed for minimal weight and higher operating temperature, but your original point that it's not worth the weight penalty is undoubtedly true.

 

[mknox]

Here's the funny part, though: I work as a senior executive at an electric utility where we are promoting EVs (we have a Volt), but no public or employee charging infrastructure! This is something I'll be tackling with the senior leadership team, and I hope to be able to promote some charging infrastructure at local malls and so forth.

Problem solved. We have re-worked our Strategic Plans, and I am now the executive sponsor responsible for promoting EVs and EV charging infrastructure. Will be presenting proposals to our Board next month.

 

[KBF]

Problem solved. We have re-worked our Strategic Plans, and I am now the executive sponsor responsible for promoting EVs and EV charging infrastructure. Will be presenting proposals to our Board next month.

Congrats! It's nice to have your "hobbies/passions" mix with work.

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For those concerned about variability in braking due to regeneration limits; I've experienced the same thing (due to full charge, haven't tested out the cold) on my Zero motorcycle. I didn't notice for a few weeks because I was being cautious, but I once I started relying on regen, one morning I was in a rush, and wasn't paying attention, and at the first stop sign (on gravel) I almost lost control due to suddenly having to slam on the brakes. After the second time I realized exactly what was happening and now I'm always prepared. It is very predictable, too. So I tend to agree that it just is something to be aware of, get used to, and is actually very useful for cleaning the brakes. That first stop sign is pretty much the only time I have to solidly use them.

It absolutely should be mentioned by the DS.

 

[jerry33]

Except that resistors can't tolerate the temperature levels that a slab of steel can. The brake rotors on your car get quite hot.

Right. It's not all that hard to make them glow red. It would have to be a heck of a resistor. If you were really going to do something like that a flywheel might be a better choice.

 

[Doug_G]

However, an example from that site quotes 60kg weight for a 25kW device (including its protective cage), so that isn't a practical solution. You could probably do better with something designed for minimal weight and higher operating temperature, but your original point that it's not worth the weight penalty is undoubtedly true.

Well yeah, I was assuming you weren't going to use industrial sized equipment here.

 

[eledille]

JRP3 re internal resistance: Aha, thanks, that seems reasonable.

Well yeah, I was assuming you weren't going to use industrial sized equipment here.

This is completely academic of course, it's not going to happen and the disc brakes need exercise anyway. But exactly this sort of electrical brakes are widely used for trains and trams, and I would bet they can be more effective per unit mass than disc brakes.

This type of resistor can tolerate up to 1000 deg C. Resistance rises with temperature, so they are somewhat self-regulating, and if you install a blower they will automatically absorb more energy due to lower resistance. How much energy you can dump into them is determined by how fast you can remove the heat, and you can arrange for them to have much more surface area and airflow than a brake rotor. Our city trams have arrays of such brakes complete with blowers on the roof.

If you heat a brake rotor at 2 kW for a while it's going to become very hot, but a cheap heat gun will happily burn off 2 kW indefinitely. Replace its tiny fan with a proper blower for five times more airflow and make it five times bigger, and you can dump 50 kW into a very small and lightweight package. Make sure the fan doesn't fail, though, that would result in some serious fireworks. But I can't imagine they would be allowed to sell a car without mechanical brakes anyway, so there's not much point. Some images here.

I think a better "regen limited" warning should be good enough and much cheaper

 

[cinergi]

Parked all day in < 40F weather. Was 34F when I left work. Regen was limited further - just below 15 kW. It quickly moved up to 30 but was in the 30's for quite a while. After I got through about 2/3's of my commute (18 miles, mostly highway), the limiter went away.

 

[hcsharp]

Parked all day in < 40F weather. Was 34F when I left work. Regen was limited further - just below 15 kW. It quickly moved up to 30 but was in the 30's for quite a while. After I got through about 2/3's of my commute (18 miles, mostly highway), the limiter went away.

Hmmm... I think I'll keep my Roadster. It was parked outside today unplugged hovering around 34 deg F (1C). The high was 35, low 30. Drove home with full regen.

I understand the MS battery has a lot more surface area exposed to cold, but it almost appears like they're limiting regen more than the Roadster. I'm puzzled. And not looking forward to this behavior in the winter months.

Is there any way to get the display to show you vitals like the battery temp?

 

[ChadS]

No way to see data like battery temp. At least not yet; I'm hoping that will come in a future update.

Today was mid-40's or so, and regen was limited when I turned the car on. Like you I'm surprised as the Roadster would definitely not have any problem there. But it goes away quickly when you are driving.

 

[huntjo]

Have noticed this a lot here, with night temps in the low 30s and days not much above 50s. Range is a bit affected due to less regen potential, but I tell myself, that the car is just smart enough to protect the battery from charging under non-optimal conditions. :smile:

 

[strider]

I understand the MS battery has a lot more surface area exposed to cold, but it almost appears like they're limiting regen more than the Roadster. I'm puzzled. And not looking forward to this behavior in the winter months.

Remember that the 85kWh packs are a different chemistry than the Roadster. Maybe they are more sensitive to being charged when cold? Perhaps JRP3 has some insight...

 

[mnx]

I wonder who will be the first to cover the bottom of the battery pack with spray foam.

 

[arg]

I wonder who will be the first to cover the bottom of the battery pack with spray foam.

Do you actually want insulation while driving, or is there enough heat to be got rid of that you are actually winning through not having to run the cooling pumps so much? Also not clear if it's just air temperature that's relevant, or if when driving in snow (city streets) the effect of slush spraying on the bottom of the pack is conducts significantly more heat away than airflow alone in cold but dry conditions..

I was wondering if a simple solution just for parking would be worthwhile - given that the underside of the car is fairly flat, you could have a bristle structure that you simply drive over and provides a bit of insulation (particularly obstructing airflow). I was thinking of something equivalent to a bunch of broom heads fixed to the floor. Obviously only works for covered parking rather than outdoors, but if it worked would be a no-hassle way to keep the temperature up after driving in and/or avoid heat loss during charging. In summer, just roll it up and put it away.

Crazy?

 

[JRP3]

I'm not aware of any cold weather specific limitations of the new chemistry over the old. It may be as simple as finding life cycle benefits from limiting regen in the cold. In other words, Roadster owners may enjoy the greater cold weather regen but it could come with a price. Personally I'd rather wear my brake pads a little more in return for a healthier pack :wink:

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Crazy?

Yes :biggrin: It might help some but you'd want an airtight system, hence the foam idea. I'd use foam board insulation, one inch thick might be enough, you could use an adhesive that allows removal, double stick tape or something.

 

[mnx]

I'd use foam board insulation, one inch thick might be enough, you could use an adhesive that allows removal, double stick tape or something.

Foam board sounds like a much better idea. My money is on KBF to do it first since he lives in Manitoba...

 

[KBF]

Foam board sounds like a much better idea. My money is on KBF to do it first since he lives in Manitoba...

Nope, I have a well-insulated attached garage, and a detached heated garage if necessary. My wife will have it outdoors 2 days a week in winter, but her job requires her to drive from one hospital to another in a nearby town at lunch, so it won't ever really sit outside for more than 4 hours at a time. And I'm thinking our winter road trips will be mainly South in nature I suppose I'll have to be careful when we're at my parents' cabin; I might have to convince them to put up a temporary car shelter for winter... not so much the regen issue, but for charging enough to get home.

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And I will only bring it to the cabin once my jumpseats are installed... So others may beat me to find "insulation solutions"

 

[efusco]

22F-24F here this morning. My DS (and this thread) had warned me about reduced output and regen in cold weather and the dashed line indicator on the dash display when this occurred. Did notice reduced regen a few days ago, but hadn't noticed the dashed line at the time. Today, though, I had my out for it.

Something interesting to note is that at 22F the line was at about 13kW, but max regen actually displayed was about half of that. Likewise, when the line moved up to 30kW I was getting maybe 15-20kW of regen. But once it got to 60kW for the line I was seeing nearly 50kW of regen...almost full It took around 10 miles of driving for the line to move from 13kW-60kw.

Despite the temps being in the low 20s my max acceleration was not limited.

Dash and touchscreen display by efusco, on Flickr
*I notice the dash says 30F, but other area thermometers were reporting ~24F when I went out at noon.

 

[cinergi]

You'll get a fraction of the max at lower speeds. I can't remember, but I suspect you'll get closer to the yellow line if you let off the accelerator at 60 MPH.