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Weak Regenerative Braking - Range loss in hilly terrain
- Thread starter Bob Denny
- Start date
Did you start it from dead cold without preheating? I've noticed occasionally in winter (on my 4th winter with this thing) if I haven't preheated I'll only get about 40kw of regen, which isn't enough on a steep grade, until the battery is all the way warm, and the car won't necessarily tell you it's reduced (no dots on the regen bar on the dashboard, but regen still limited as if I'm cahrged to 95+%) In my experience, normal highway driving isn't enough to get it back if it's cold out, and if it's cold enough, it can even get worse during a drive unless you yo-yo- it or navigate to a supercharger to warm the battery up. And regen itself doesn't warm the battery much either. I'll go whole 30-40 minute drive never getting full regen unless I take steps to warm the battery, when it's cold out and/or the battery has cold-soaked, even without a warning on the dash. The reduced regen warning seems to go away fairly quickly after starting to drive, but the regen doesn't come fully back until much later.
And I know it sounds stupid, but if you had a stiff headwind or crosswind on your downhill sections, the regen won't be able to harness much energy compared to what the prediction expects due to elevation change, because you're fighting the wind. What is the dashboard energy readout saying?
And I know it sounds stupid, but if you had a stiff headwind or crosswind on your downhill sections, the regen won't be able to harness much energy compared to what the prediction expects due to elevation change, because you're fighting the wind. What is the dashboard energy readout saying?
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In my experience in my 2017, the lack of a "dashed out" section isn't an indicator of full regen capability, at least according to my butt dyno. Sometimes, regen feels less in the morning when the garage is cold and there is no dashed line (vs summer driving), and other times, regen feels less even though the dashed lines have disappeared because the battery has warmed in winter weather (again, vs summer driving).
Exactly. You'll still get reduced regen even without an alert on the dash. I believe these cars will do up to 100kw? I stop seeing the regen reduced dashed line when it will get to the 50kw mark
Well, this isn't a new thing for me, but I see that you have AZ listed as your location. I'm guessing relatively recent updates have increased the temperature at which the battery is considered "cold." I seem to have it regularly in the 50's now where a year or two (and several versions) ago, it didn't consistently happen when it was that warm. Put another way, if I had that happen in the 50's two years ago, it was because it had been in the 30's when I parked, but this year, it happens straight from being parked in my 50 degree garage overnight even though charging occurred.
I'm not sure how cool San Diego gets, but even if San Diego is generally warmer than the temperatures I'm discussing, if there are mountains on that route where it gets cooler in addition to the grades being steeper, what I'm explaining could certainly be more noticeable now than in the past. To be clear, I don't think I ever noticed a reduction in regen with charge below 90% and consistent ambient temperature above 50 degrees F until relatively recently, but now I sometimes notice a reduction in regen with charge above 85% and/or temperature above 50 degrees F. For me, while the reduction without dashed lines has always been a thing, it used to only be noticeable when there were dashed lines that just disappeared or would soon be showing up, and this was at cooler temperatures (below 50 F) or higher charges (above 95%) until Spring 2023 (or better put, since it would be difficult to observe during the winter when there are usually dashed lines, after Fall 2022). While it is possible some change of mine is relevant, it seems more likely that Tesla changed variables/settings which also affected you in the same way. Also, keep in mind that while the ambient temperature isn't directly relevant, the battery temperature is, making "consistent ambient" an important distinction with regard to the temperature because that indirectly affects battery temperature (when it's colder while parked, dashed lines will appear even though it has warmed up, when it's warmer while parked, regen might still be full strength even though it has cooled off). Based on my observations, the points when the dashed lines will appear and disappear have changed along with this, but that doesn't detract from the abbreviated quotes above or the discussion in this paragraph where they aren't present.
It is possible, however if this is a software change, and it results in a decrease of regen, then the trip energy prediction (gray curve) should reflect the change and still give you a good prediction. Instead the prediction is off in the "optimistic" direction, not good. In my case it was probably around 50 deg, but I had been driving at freeway speeds for well over an hour (80 miles) before starting the first descent. Also climbing requires well over 400 Wh/mile in my X and the internal resistance of the battery should have provided plenty of heat to bring the battery temperature well above 50 deg.
I can't say that I disagree with this, but I can fathom that the battery management software gets updated separately and faster than the prediction software.
I agree this also sounds like enough to me (80 miles at 400 Wh/Mile seems likely to get the battery really hot unless it's well below freezing), but to be clear, when I say above/below 50, I mean something more like 50-60 vs 40-50, it's just an observational difference I've noticed over time. Actual optimal battery temperature is likely significantly higher than consistent ambient air temperature regardless, though, so for an example with no scientific or documented backing simply to explain some theory, if they now require the battery to be 100 F for max regen where they previously required it to be 90 F for max regen, it is feasible that 50 F cools it too much for it to reach max regen under those conditions where it wouldn't have done the same under the prior constraints.
Some mixed results. You were tracking very well for most of the drive. At the Mile 85 downhill your actual regen didn’t match predicted but eventually predicted and actual became aligned at Mile 100. Focus should be on that.
Is that a sudden tailwind/headwind change thing?
Like you had a headwind going downhill, driving less regen to maintain speed. But then you ended up with a tailwind reducing your energy consumption.
The slight downhill at Mile 75, actual and predicted aligned.
Tell more on this downhill portion at Mile 85ish. What is special about it? Is there a heading change?
Is that a sudden tailwind/headwind change thing?
Like you had a headwind going downhill, driving less regen to maintain speed. But then you ended up with a tailwind reducing your energy consumption.
The slight downhill at Mile 75, actual and predicted aligned.
Tell more on this downhill portion at Mile 85ish. What is special about it? Is there a heading change?
Those are some good points. I assumed it felt like you needed to use the brake more than you have in the past and didn't pay much attention to the chart. Another possible difference: were you using FSD beta this time and not in the past? FSD beta is far less efficient than a driver who is trying to be efficient, amongst other things, it brakes way more than TACC did and could potentially have an impact here. 500 miles probably isn't enough to make your front wheels extra dirty from brake dust, but if they are and weren't before that'd be fairly telling.
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