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Strange question about regenerative braking

Hey. I have an odd question. I know that regen braking is reduced or eliminated when it's cold. But I've noticed something odd, that has me a little worried.
Generally, when it is cold, you'll get the warning about reduced regen braking right away. However, I park overnight in my garage, which is usually 55 degrees. I've noticed on cold mornings, it takes the outside temperature reading on the car a LONG time to get down to real outside temperature upon leaving my garage. Sometimes as much as twenty miles of driving. I also don't get the Reduced Regenerative Braking messege until about half-way through that drive.
My concern is that because the outside temp sensor is so wrong for much of the drive, that is actually allowing regen braking when it shouldn't be, until the temp sensor catches up to the real outside temp.
Thoughts?
 

jcanoe

Well-Known Member
Oct 2, 2020
6,031
6,714
Maryland
If you see dots on the left side of the power bar (the thin grey bar at the top left side of the screen then regenerative braking has been reduced based on the state of charge of the battery, temperature of the battery. The dots are an indication of how much regenerative braking is not available. If the Tesla vehicle eventually displays the notice that regenerative braking is reduced due to temperature nothing will change.
 

jcanoe

Well-Known Member
Oct 2, 2020
6,031
6,714
Maryland
Ok. I'll check for the dots in the morning. If they are not there, then I need a service visit for the temp sensor. It needs to react much quicker
The outside temperature sensor in my 2020 LRMY gives an updated reading fairly quickly. Even so, sometimes the Reduced Regenerative braking notice is not always displayed right away. I'd let it go, unless your outside air temperature sensor is giving erratic readings. (Recently there was a post about the temperature sensor giving false reading. It turned out to be that a rodent had chewed through the wire harness for the sensor.)
 
There is a separate thread about the exterior temperature indicator being slow to adjust. Seems it's a lot worse if you precondition before leaving, and park in a garage obviously. No relation to regen at all as others said, but might affect the cabin heating as some seem to report. I park in a garage but don't precondition (it's warm already) so I don't see the issue.

The regen reduced message is weird. I've sometimes left home with no regen at all (battery under freezing temps) and no warning, drove a bit, parked for an errand, and had the message when I started driving again. The battery had warmed a bit and now instead of not having any regen I had partial so the car told me :) Don't worry about the message, just look at the dots as indicated higher up.
 

Pianewman

2021 MYLR VIN 88,XXX, Rd/Wh, 12/20 delivery
Supporting Member
Oct 28, 2020
2,321
1,999
Fort Worth
Regen is based on the temperature of the battery, not the outside air. When you leave the house the battery is 55F and takes awhile to cool down closer to the temperature of the outside air. The battery is big! So the temperature changes slowly.
Is this true? I thought regen was reduced when ambient temp falls below a certain point, to keep aggressive regen from locking up the wheels.
 
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Ok. I'll check for the dots in the morning. If they are not there, then I need a service visit for the temp sensor. It needs to react much quicker
I don't think you have to worry, outside temperature doesn't impact regen braking. It is the temperature of the battery. You can use Regen in cold weather. The limited regen is only until the battery is warmed up.
 
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Regen is based on the temperature of the battery, not the outside air. When you leave the house the battery is 55F and takes awhile to cool down closer to the temperature of the outside air. The battery is big! So the temperature changes slowly.
The outside temperature sensor in my 2020 LRMY gives an updated reading fairly quickly. Even so, sometimes the Reduced Regenerative braking notice is not always displayed right away. I'd let it go, unless your outside air temperature sensor is giving erratic readings. (Recently there was a post about the temperature sensor giving false reading. It turned out to be that a rodent had chewed through the wire harness for the sensor.)

One of those Tesla quirks, the actual regenerative braking restrictions are based on battery pack temperature, but the "regen may be reduced due to cold temp" warning is triggered by the exterior temperature sensor. I am not 100% sure but I think the warning specifically says "may be" reduced, not "is" reduced... if the warning message was based on the battery pack temperature it would say "is" reduced.

Keith
 
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They could solve a lot of confusion by providing more detailed information in many situations: battery temperatures, powers, explanation of why charging is slow etc... They instead choose to reduce information and make it "just a car" so it appeals to the masses. I don't know if it's the best solution but it's the one they currently chose.
 
They could solve a lot of confusion by providing more detailed information in many situations: battery temperatures, powers, explanation of why charging is slow etc... They instead choose to reduce information and make it "just a car" so it appeals to the masses. I don't know if it's the best solution but it's the one they currently chose.

Nope, they chose to make it "just an iPhone" not "just a car"... if they were treating it like a car I would have a manual latch on my glove box.

Keith
 
To clear up any confusion, outside temperature has a large role in reduced regen. If it is cold outside (or where you store you car overnight) the battery will be cold. However, the regenerative breaking controller is not using the displayed outside temperature on your screen to control regen as others have mentioned.
 
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