After heating charge, cooling added 7 miles

[bwilson4web]

My SR+ Model 3 is normally set for 66% SOC and typically the GOM shows 156-158 mi after L2 charging at home. The higher range is listed after the car sits on the L2 charger for a couple of hours. But something strange happened today:

• The car had been parked a week and the GOM showed ~144 mi due to parasitic losses.
• Plugging in to the L2 quickly brought the GOM to 156 mi.
• After ~30 minutes, I turned on climate conditioning and ~8 hours later, the GOM reached 158 mi.
• About 6 hours later with the car parked in a work area, the GOM showed 164 mi.

Bjørn Nyland's recent YouTube videos show his Model 3 raises the battery temperature when charging and lowers the temperature on the road. In effect, this recreated what Bjørn documented as built-in to the Model 3 control laws: heating battery during charge followed by cooling for operation.

This begs the question of what happens if charging to 100% is combined with climate conditioning to warm the battery and then letting the car cool. Would the GOM show over 240 mi?

Bob Wilson

 

[Pushmi-Pullyu]

Bob, do you think any of this is really affecting the car's actual range? Or is it merely messing with the way the car estimate range? My guess is that raising the temperature of the battery pack above normal room temperature (72° F) isn't going to help much, if at all. As one auto exec once said about li-ion battery pack operating temperature: "If you're comfortable, the batteries are comfortable."

I confess I don't get this thing about Tesla "pre-warming" the battery pack for faster Supercharging, or for "launch mode" for drag racing, unless it's cold outside. Do li-ion batteries have a higher power capacity when warmed up hotter than room temperature? Or is that true of the specific chemistry that Tesla is using in its cells, but not true of other types of li-ion cells?

And if Tesla's cells do have a higher power rating when warmed up beyond room temperature, just why is that?

Inquiring minds want to know!

 

[bwilson4web]

Actual range, I don't know but then I've not done any Guess O Meter (GOM) calibration runs. So far, it has been 'close enough' as the miles remaining get smaller and more accurate while approaching my next Supercharger. But the reason this has merit are the lawsuits claiming the Model S/X battery packs are defective.

I've read the 102 page, David Rasmussen complaint and realized his whole claim about 'lost range' is dependent upon the Tesla estimated range number, the GOM. In fact all claims are based on Tesla software reported values. I would feel much better about a lawsuit that has a 3d party, engineering team instrument the car.

As for the temperature effects, one YouTube report claims deposition of metallic lithium at the anode (carbon) is reduced by charging at a higher temperature. Discharging at 'room temperature' seems to be the Tesla approach. Sad to say, I've not studied scientific and published papers but this makes sense: charge hot and discharge cool.

Charging LiON requires the carbon anode to hold the lithium ions. A higher temperature should make ion movement easier into the graphite matrix so they don't collect on the carbon surface and precipitate as a metal. The risk is if the electrolyte decomposes leading to lithium ion capture in non-active salts and compounds.

Bob Wilson

 

[Pushmi-Pullyu]

...the reason this has merit are the lawsuits claiming the Model S/X battery packs are defective.

Isn't that just a tiny percentage of S/X battery packs made during a certain period in the past; just the ones for which Tesla used an OTA update to reduced their maximum charging rate, and the suit also claims that range is reduced? Altho, as you note, it may well be that only the way the car calculates range was changed; there may not be an actual reduction in range.

So far as I know, the lawsuit doesn't cover all Model S/X cars, just a relatively small group of them.

As for the temperature effects, one YouTube report claims deposition of metallic lithium at the anode (carbon) is reduced by charging at a higher temperature.

Interesting! I knew deposition of metallic lithium in a layer which would completely, permanently ruin the battery cells was a problem with charging the battery faster than a trickle below freezing temperature (or slightly above it), but I didn't realize that was a problem when Supercharging. I would guess the effect is much, much weaker from Supercharging, since we know that some Model S's and X's have been Supercharged hundreds or thousands of times without the pack becoming unusable. On the other hand, that might explain why Tesla programs their cars to count the number of Supercharger uses, and if that count exceeds a certain sum, then the car slightly reduces the maximum Supercharger power level. In the past that has been explained as Tesla not wanting the battery packs to be worn out prematurely, but you may be pointing to a more precisely identified cause.

I am often amazed that, despite all I've read about Tesla's EV engineering, there is still so much more to learn! So thanks again for your engineering-oriented posts, Bob. Much appreciated!

​

 

[bwilson4web]

“Bjørn Nyland's recent YouTube videos show his Model 3 raises the battery temperature when charging ...’

The YouTube videos shows during charging the two motors are in “heat generation” mode leading to a higher battery coolant temperature into the battery. This is different than ordinary battery ohmic or exothermic heating. The coolant inlet versus the battery temperature clearly shows the Tesla control laws heating the battery.

I’ll add the YouTube links and critical time stamps when I get back to the house:


Playing the YouTube frame-by-frame, I entered in a spreadsheet:

• video time stamp (mm:ss)
• vehicle clock (hh:mm)
• battery power - charging is a "-" so I converted it to positive for charting
• Cell temp mid C
• Battery inlet C
• Battery flow lpm
• F power
• R power

This is the chart, @Ed Woodrick :

• 00:00 to 2:20 - the two motors go into resistance mode generating heat they transfer to the battery coolant. This brings the battery cell temp above 41C and it quickly tapers off.
• 2:30 to 3:20 - end of heat generation becomes power to charge the battery.

Perhaps you might try the same protocol and see what you get?

Bob Wilson

ps. Yes, the GOM gives a WAG, a nice WAG, but 'your mileage may vary' (YMMV).

 

[Pushmi-Pullyu]

41° C = 105° F. I thought the battery pack "liked" to keep the cells below 100° F? And that charging cells at a temperature above 100° F was bad for them? Or does that apply only to cells with a different chemistry than the high energy-density cells Tesla uses?

Seems the more I read about battery pack tech, the less I know!

 

[bwilson4web]

Bjørn Nyland has been one of the first to get Tesla Model 3 engineering data and it has been an eye opener.

Skipping down to 6:59, charging stops at 29.8 kW and the cell temperature is 50.8 C. Now the coolant is cooler, 45.4 C, and the battery coolant flow, 12.0 lpm. I used similar engineering data from our Prius to learn how to drive the car for maximum range and efficiency.

Near as I can tell, this (my?) protocol has not been described before:

• L2 charging - reaches the limit and stops without raising the battery temperature
• pause 30 min to let it normalize and put a distinct break in the charging data
• Pre-conditioning ~6 hours - in cold weather, this turns on the heater(s) which also raises the battery temperature. But as the battery warms, there are short charging sessions that add charge to the battery. It is as if the battery voltage actually goes down as the cells warm up allowing more charge into the battery. There are at least 5, full scale, charging events with the warming load.
• stop pre-conditioning so battery temperature returns to ambient cooler temperatures
• monitor the indicated battery range which rose to 165 mile which at 66% means 164/.66 ~= 248 miles

One of the things an engineer does is be data driven. A good background in physical sciences and math is important BUT you never close your eyes to metrics. Not everyone has the self-discipline to be data driven.

I'm not sharing this data with the "Tesla Motors Club" group because they have too many ad hominem and "Read The Fine Manual" (RTFM) members ... an unfortunate pattern we both are too familiar. Rather, we are following in the path of Galileo who once complained, 'Look through the telescope.'

Bob Wilson

 

[bwilson4web]

I finished up a full session chart only to discover he'd done a little 'creative' editing. One part of the video had been moved. This coincides with some anomalies in the data. Regardless, this is the full graph:

• Initially the motors (lower two lines) are in resistance mode and as they warm up, the coolant pump (blue line) transfers the heat to the battery.
• ~28 min., the battery reaches about 41 C and the motor heating turns off. The coolant continues to flow transferring the last of the heat. There is a step increase in battery charging since the motors are no longer drawing power for the EVSE.
• ~46 min., the cabin heater was probably turned on which reduced the battery charge rate and turned the motors back into heaters.
• ~1:12 hh:mm, the charging came to an end and the car began cooling down the batteries using some of the charge.
• The battery heating and cooling are technically lost because they do not provide motive power. But they are needed for battery health and longevity.

Later today, I may try to resolved some of the data spikes with more data points. However, I doubt it will significantly change the overall results.

Bob Wilson

 

[Pushmi-Pullyu]

...as the battery warms, there are short charging sessions that add charge to the battery. It is as if the battery voltage actually goes down as the cells warm up allowing more charge into the battery. There are at least 5, full scale, charging events with the warming load.

Li-ion battery cell capacity is dependent on temperature. So, the higher the temperature, the higher the capacity. I don't know if that's why the BMS charges the battery in bursts as it warms, but at least it's capable of holding a greater maximum charge. What you don't want to do, however, is charge it to 100% or near 100% when it will be cooling down afterward. That results in overcharging... which, from what I've read, can lead to permanent damage (and reduction in capacity) to the pack.

Source of the graph above: https://www.powertechsystems.eu/home/tech-corner/lithium-ion-battery-advantages/

...they have too many ad hominem and "Read The Fine Manual" (RTFM) members ... an unfortunate pattern we both are too familiar.

Gosh yes, I'm sure that the "F" in RTFM means "Fine", just as it does in "RTFA" on Slashdot (Read The F--- Article).

I mean, what else could "F" possibly mean in that context?