I had another really cold morning commute. This time it was 6 degrees F, and my average consumption for the trip was 267 wh/mi. That's over about 50 miles with a car that was charged and preconditioned overnight.
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Model 3 SR+ LFP Battery Range, Degradation, etc Discussion
- Thread starter Baluchi
- Start date
Good info, thanks.
Have you ever found yourself in a situation where it's really cold and you can't precondition to warm the battery? I'd be interested in your wH/mile under those conditions.
Did you use scheduled depurture or pre conditioned in the morning with climate control? How long would you say to pre condition before driving the car is ideal?
Not really cold. Like right now I'm about to drive home with a cold battery and outside temps at 28 degrees F. But my efficiency will be better than it was this morning with a preconditioned battery. Even though it's still cold this afternoon, the difference between 6 degrees and 26 degrees seems to make a big difference in consumption, and preconditioning doesn't overcome that difference on a long drive.
It charged from 00:30 to 04:40. Then the climate came on at 05:40. Then I departed at 06:00.
I'm sure the battery was decently warmed duringfour hours of charging. When I got in the car, the battery was at 73 degrees F. By the time got to work, it was 62 degrees F. So it actually cools down and loses regen while I drive to work every morning in this kind of weather.
Thanks. The "bench test" in Limiting Factor's video seems to indicate range isn't much affected until around -10C (14F) so what you observed seems to confirm that.
That's interesting. I'd hesitate to say it isn't much affected until 14 F, but there does seem to be a big drop in efficiency under 20 F. But I could imagine the difference between 30 degrees F and 60 degrees F may not be huge if you're just running at highway speeds over flat terrain. But throw in a bunch of hills and 60 F starts to look a lot better due to the availability of max regen. Then there's how you're using your climate controls, how heavy you are with the accelerator, etc. Lots of variables that make it all fun to play around with.
But take everything I say with a grain of salt because I'm still trying to decode it all myself.
Makes sense. I've seen regen loss while driving when it was maybe 40 F and raining. I don't have scan my tesla, but based on the decreasing regen I assume the battery was getting colder as I drove.
Yes, for sure your battery was getting cooler as heat was ported to other systems. It seems counterintuitive that your battery will cool off while driving, but it does if the outside temps are even moderately cold. I always watch the battery inlet temp when I turn on the HVAC, and it usually drops a few degrees as that warm fluid is (presumably) re-routed to provide heat in the cabin. It really gives you an appreciation for how advanced Tesla's thermal management is, and how they're trying to squeeze every ounce of efficiency out of the cars.
Just a quick comparison to yesterday. I did the exact same drive this morning, but it was 28 degrees F instead of 6 F that it was yesterday.
6 degrees F: 267 wh/mi.
28 degrees F: 217 wh/mi.
So even though temps were still below freezing today, I only needed 81% of the energy to make my drive.
One side note, I when I turned on my heater during my drive, I watched the battery inlet temperature drop all the way from 77 F to 63 F. At that point my battery started to cool down as the heat was diverted to the cabin. It's been said a million times, but if you're trying to maximize efficiency, avoid using the heater when possible.
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Sorry I didn't read the 19 pages so probably ask something already answered. But just in brief
- Do we know if it is actually healthy to regularly charge to 100%. I seemed to have read somewhere it is necessary for the battery to calibrate but not necessarily optimal in relation to degration?
- Do we know how it degrades compared to the LR batteries?
- Do we know if it is actually healthy to regularly charge to 100%. I seemed to have read somewhere it is necessary for the battery to calibrate but not necessarily optimal in relation to degration?
- Do we know how it degrades compared to the LR batteries?
For LFP batteries, it's healthy to charge them to 100%. Probably not unhealthy to have them below that, but they do not suffer cumulative damage from being charged to 100% like NCA batteries do.
Battery degradation is better for LFP than NCA batteries. They will lose a little charge over time, mostly in the first year, but after that will lose much less charge over their lifetime than NCA.
Also, they're safer (less likely to suffer thermal runaway and catch fire if punctured), but they are heavier and perform slightly worse in the cold.
No. LFP batteries are just like all other lithium batteries - the lower the average state of charge, the slower they will lose capacity over time (calendar life losses). @AAKEE has posted numerous references to this. And the more you charge to 100% (especially if you let it sit there), the faster they will lose capacity.
LFP batteries have shown to be very durable when it comes to rapid cycling - but I haven't seen anything that claims that 100% SOC is "healthy" for any lithium battery. In all cases I've seen, 100% is the worst.
Here is a link to a study which looks like 5 different scenarios to model calendar aging - the cells stored at higher states of charge and higher temperatures clearly lose capacity much faster than cells stored at lower states of charge and temperature.
This myth about 100% being OK only came about because of the flat voltage curve of LFP batteries - charging to high SOC regularly is required to help the BMS keep track of each individual cell's SOC. But that doesn't mean you should charge it to 100% and leave it there.
5 20% cycles is not the same as 1 100% cycle. Shallower cycles do less damage to a battery than deeper cycles.
Depending on the specifics of the battery, you can get quite a bit more energy in/out of the cells with shallow cycling. For example, cycling the battery between 40-60% vs 0-100% can get you somewhere between 3-10x the useful life of the battery.
Tesla Recommends Charging Model 3 RWD's LFP Battery To 100%
Tesla has issued revised charging guidance for the entry-level Model 3 RWD equipped with equipped with lithium iron phosphate (LFP) battery cells.
insideevs.com
Sooo, why does Tesla say keep them at 100%?
Tesla Recommends Charging Model 3 RWD's LFP Battery To 100%
Tesla has issued revised charging guidance for the entry-level Model 3 RWD equipped with equipped with lithium iron phosphate (LFP) battery cells.
Sooo, why does Tesla say keep them at 100%?
Quoted from Tesla Model 3 Owner's Manual | Tesla
In other words, it's all there to work around the shortcomings in the BMS because it loses track of the state of charge of each cell, over what appears to be relatively short periods of time. If Tesla truly thought 100% was good all the time - why even have a 50% SOC option?
Also keep in mind that Tesla doesn't really care how long the battery lasts - the LFP battery only has to make it 8 years / 100 k miles while keeping >= 70% original capacity. I have no doubt that with normal temperatures and driving habits, > 99% of the cars will meet that. Perhaps cars in Phoenix, Arizona might start having issues.
Tesla should make this dead-simple for LFP (and all) cars. Keep track of how long and how many cycles the car has gone without a "high enough" and/or "low enough" charge for the BMS to better estimate cell SOC and capacity. If the BMS needs more information at a specific SOC to balance the pack, then tell the user "Hey, charge to 100% this time to help the BMS out" or "Hey, run the battery down to 15-20% this time to help the BMS out". And depending on pack temperatures, start using pack energy to cool down the pack if at very high SOCs - this will slow down calendar losses by cooling down the pack as well as reducing the SOC.
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