Physicslawyer
Member
My 9/22 MYP is at 80% now and is showing 237 miles. The car has 3k miles on it. It's 31 F outside now.
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Is it normal for an 80% charge to show 228 miles with MYP?
- Thread starter Krakatoa
- Start date
When the battery is cold Tesla now lowers the range and SOC by 3%. Tesla does this to provide a more accurate range estimate. If you park with 80% SOC you might observe 77% SOC the next A.M. even if Sentry mode is Off.
AlanSubie4Life
Efficiency Obsessed Member
You should check and see if it is allocated to Standby drain while parked, on the Energy Screen “App.”
It’s pretty common at this time to see BMS adjustments in moderate temperatures 50-70 degrees with no temp changes which result in 3% loss of available energy.
Happened to me just this morning with my 3 (as it does most mornings). Finished charging at 175 miles (added 49 in 1:19) and less than two hours later was at 167 after a sleep cycle. Energy screen? 8 miles since last charge. Comfy 64 degrees. “Lost” 15% of the energy added!
I need to go and calculate the effective efficiency but I think it is just optimistic about how much energy it has added to the battery (possibly a bug) during charging. Also of course the car will “generate” energy later and add miles in most cases. Between the two it might make sense.
If I calculate (1:19, 240V@40A, 234Wh/rmi) with the 41 miles added I get 77% efficiency which is too low at 40A. But if I use 49 miles added I get 92.5% which is too high. Reality is probably around 88%, so hopefully my car gives me back 5-6 miles at some point then it would all work out perfectly.
Who knows. Also explains why many miss their charge targets (was not always the case)!
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Clarification requested.
A fixed 3% reduction? As opposed to how it was previously with a variable reduction (blue shaded area of battery icon plus the snowflake icon) based on actual battery temperature? The previous reduction could be anywhere from 1% to almost 10%.
As far as I am aware the blue snowflake is a cold battery indicator. This also means you can expect decreased performance (available power), reduced regenerative braking. Anecdotally after charging I and some other Model Y owners have observed a loss of 3% SOC after the Tesla Model Y has been parked overnight in cold, i.e. 40F or colder temperatures.
I have not experienced the displayed SOC dropping by more than 3%. Lots of questions remain. It appears the 3% reduction is only applied once per charge cycle. SOC does not charge drop by an additional 3% the following night in my experience. Somehow the Model Y's battery management system knows when to apply the 3% reduction. I believe if Tesla was more open about cold weather battery performance the decrease in effective capacity might be ~10%.
AlanSubie4Life
Efficiency Obsessed Member
This has little to do with cold weather as far as I can tell. Admittedly, for a Model 3.
It has been a steady 63-64 all day today here. I saw it this morning. It just takes a short sleep cycle after a charge and if it is going to take a massive 8-mile dump, it will. As illustrated above, definitively. This is quite repeatable on my car at this charge target. Every time? Maybe not. But most times.
Good news is my car just gave me 6-7 miles back, netting a loss of 2 for this cycle, which takes efficiency as calculated carefully above, to 88-89%, which is exactly where we’d expect it based on EPA documented data. This recovery is also pretty repeatable (note that the car does NOT tabulate it on the Energy Screen running total however - have to look at the graph).
It is annoying but it is basically a random BMS walk to the right answer.
In the Model 3 thread there is a rather extensive amount of data on how this behaves, which I will probably add to for posterity.
It will likely be accurate until the next software update, and then everything will change again.
This was at a normal temperature, garaged, short charge cycle, so minimal heat added to the pack (specifically about 1.3kWh of total heat losses everywhere on the car, and probably only 50-75% of that to the pack). Someone can do the math (using Green’s functions, etc.) on how much of a temperature change that would be - fairly small I would suspect. Note also miles were gained on a cooldown after driving. So deltaT not likely causative here.
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I almost never display the estimated range or miles added while charging. I only track % state of charge (SOC) when I begin charging, at completion of the charging session (up to 90% SOC), while driving and when waking from sleep mode. I don't use Sentry mode when parked at home. The 3% drop is SOC only seems to happen overnight immediately after a charging session (I usually charge my Model Y between 6:30 PM and 8:30 PM), a short 4 mile drive back home. This happens if the temperature drops below 40F overnight, inside the garage. In the A.M. the interior of my Model Y and the garage temperature are usually within a couple of degrees of each other when I start preconditioning. The 3% battery SOC drop is immediately apparent (when it happens) as the last SOC changes immediately to 3% less SOC as soon as the Model Y wakes from sleep mode.
On the drive home following charging there is a good deal of variability in consumption, i.e. +/-20%. Factors such as temperature require the HVAC to work harder, wet roads (as happened this evening) could increase consumption by an additional 15%. The efficiency can vary from ~240 Wh/mi to ~310 Wh/mi with 266 Wh/mi being the long term average. The route is always the same; traffic lights aside there are few other vehicles on the road at this time. My speed is always close to the speed limit.
On the drive home following charging there is a good deal of variability in consumption, i.e. +/-20%. Factors such as temperature require the HVAC to work harder, wet roads (as happened this evening) could increase consumption by an additional 15%. The efficiency can vary from ~240 Wh/mi to ~310 Wh/mi with 266 Wh/mi being the long term average. The route is always the same; traffic lights aside there are few other vehicles on the road at this time. My speed is always close to the speed limit.
AlanSubie4Life
Efficiency Obsessed Member
Totally fine and a good way to go.
However it prevents accurately determining (net) energy added to the vehicle.
Also will happen at other temperatures.
Yes. You’ll also see the kWh added decrease (in % mode) or miles added decrease. While still plugged in. Since these are net values for a given charging session. See pictures above showing this.
AlanSubie4Life
Efficiency Obsessed Member
Coming back to add a little piece of trivia:
In % mode, the kWh added don’t represent the kWh added! They’re just the rated miles added multiplied by the vehicle constant, so will be a value which is 1/0.955 = 1.047 (4.7%) higher than the actual energy added to the vehicle (and that is assuming zero BMS errors on this quantity, which as documented above probably is not a reasonable expectation).
In the case documented above, if I had been displaying %, the car would have claimed 12kWh (49rmi*245Wh/rmi) added (out of the 12.4kWh (235V*40A*1.32hr) available from the wall, giving 97% charging efficiency (clearly not obtainable)).
Just a curiosity; doesn’t matter at all of course.
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