Ask to Tesla, Upgrade 85KW pack SC speed?

[Screwbal]

Hey All, Maybe this has come up before and I haven't seen the info but if not I figured I'd touch on it. After our last road trip taking a bit longer than normal I noticed my SC times were no where near the posted charts on the Tesla site. Their site had a chart that showed 0-80% was 40 min and 70 min from 80-100. My assumption which may be incorrect was the 70 min for 100% was the net total not the difference from 80% to 100% taking an extra 70 minutes. Our trip from 11%-80% took 47 minutes basically however the estimate from 80% on was another 40 minutes. Right there is ~90 minutes and we didn't get there with 0 which would have added time making it even longer and further from the 70 minute target.

Back on topic to my thoughts about increasing SC speed I've watched a number of videos and read many things for months and all things seem to say the new 90KW packs are charging at higher rates for longer times. The battery cooling compressor runs longer and harder on the 90KW packs than on the 85 packs (I don't have experience with smaller packs) and this had me wondering... Would it make sense to just do a firmware update to the 85KW pack cars which runs the compressor harder/longer during SC sessions which would allow more power in a shorter period?

Does anyone have any info on this as to maybe why it could or couldn't be done?

 

[David99]

Here is the charging data of the 90 battery before the software update. The 85 is very similar.

P90D Supercharging Data

The 90 battery is a newer, better chemistry/design. It's not as simple as just changing the firmware.

 

[No2DinosaurFuel]

There has been some issues with the supercharger lately. So it might not be just the car itself. The newer 90Kwh does charge faster for longer but you are still going to recover similar % as the 85kwh. So in theory the 90kwh should recover more miles faster. But as you have observed it depends on a lot of things. I would say the 40 minutes tesla advertise is the best you can get. Not the worst or even the average.

Tesla tends to advertise the best case scenario not the average or worst case. Just know how tesla's marketing machine works and you will adjust your expectation to meet it.

Going forward I expect more issues with the superchargers. I think tesla is focus on expanding as oppose to fixing current problems with the charging stations.

 

[apacheguy]

There has been some issues with the supercharger lately. So it might not be just the car itself. The newer 90Kwh does charge faster for longer but you are still going to recover similar % as the 85kwh.

Actually with the improved taper the 90 will recover % and miles substantially faster than the 85.

Tesla Ups Supercharger Charging Rate For Refreshed Model S 90D & P90D - Video

Here is the charging data of the 90 battery before the software update. The 85 is very similar.

P90D Supercharging Data

The 90 battery is a newer, better chemistry/design. It's not as simple as just changing the firmware.

Actually, before the firmware update the 90 charged noticeably slower than the 85.

At any rate, we know that Tesla is being very conservative with the taper. The 85 kWh can certainly handle higher charge rates further into the taper without much thermal stress.

 

[Screwbal]

I imagine if they let the cooling run harder and longer on the 85s the rate could stay up higher unless the battery cooling loop is just less efficient and it can't keep up. Hopefully if it's possible they do update it some time and not just leave it unoptimized because it's not the new pack that has their attention.

 

[henderrj]

It's not just the cooling, lithium ion simply cannot accept ss much current as the state of charge increases. Once it gets just so high it locks on a constant voltage and the current flow (amps) continues to drop until the battery is "full". The chemistry has to change to allow faster charging.

 

[David99]

I imagine if they let the cooling run harder and longer on the 85s the rate could stay up higher unless the battery cooling loop is just less efficient and it can't keep up. Hopefully if it's possible they do update it some time and not just leave it unoptimized because it's not the new pack that has their attention.

I have watched the temperature while Supercharging using data from the CAN bus. It doesn't seem to be the temperature that is the limiting factor. First the battery temperature goes up, but the taper hits before the temp gets critical and I saw the battery temperature drop as the battery gets fuller. So the taper curve is very conservative and unless you are sitting in the car using the AC, the car will not start the AC compressor to cool the batteries. It just uses the radiators and runs the fans at high speed. When you get back in the car and turn on the AC, you can hear the fans slow down as there is better cooling available from the AC compressor now. So based on that observation and theory, the battery could be cooled more aggressive with the AC unit cooling the battery down better.

 

[apacheguy]

I imagine if they let the cooling run harder and longer on the 85s the rate could stay up higher unless the battery cooling loop is just less efficient and it can't keep up. Hopefully if it's possible they do update it some time and not just leave it unoptimized because it's not the new pack that has their attention.

It definitely isn't the cooling. The battery only tends to get really hot at the lower end when it is charging at 120 kW. They could probably push the 90 kW cross over point out to 60% and be fine in terms of cooling. This is because the cells at higher SOC generate less heat compared to those at lower SOC.

It's not just the cooling, lithium ion simply cannot accept ss much current as the state of charge increases. Once it gets just so high it locks on a constant voltage and the current flow (amps) continues to drop until the battery is "full". The chemistry has to change to allow faster charging.

Actually, @wk057 has charged the same cells used in the 85 packs at a significantly faster rate than what Tesla is doing while supercharging. Let me see if I can dig up the post.

 

[apacheguy]

This thread has some good info:

At around 0.6- 0.7C (equiv 50-60kW DC charge) the cell seems pretty happy. Doesn't heat up significantly, but does get warm. However I'm sure Tesla's cooling loop can handle that easily. At supercharger speeds, ~120kW (1.41C) the cells heats up quickly, but slowly enough that I believe the liquid cooling loop could slow the pace substantially. My assumption is that the taper is designed more around this than actual rates the cells can take because I pushed 1.4C into a cell at 75% SoC without much issue, although the heating seemed more rapid.

I plan on doing a post with my findings on all of this once I get the data together a bit better, but, I think I have enough data to conclude that the supercharger taper below ~90% is more temperature related than anything. The cooling loop in the modules only touches each of the cells at one point on one side. If the cell is heating rapidly it only has a small portion of the overall surface area to sap away the heat, which would be impractical with rapid heating at high charge rates at a high SoC, and I'm sure the design considers and calculates this thermal data using actual internal resistance numbers for the cells.

1.4 C at 75% is 120 kW so there is no issue with the cells accepting that charge rate. However, Tesla could still be conservative with the taper, which they always will be since it is good for battery health, and probably get away with 0.9 C at 75% (76 kW on the 85).

 

[Zextraterrestrial]

Here is a 12-98.5% Supercharge w/ temps for a p85 with a B battery w/ 26k mi (march '16, fw7.1, 46~48F ambient temp)

 

[David99]

Here is a 12-98.5% Supercharge w/ temps for a p85 with a B battery w/ 26k mi (march '16, fw7.1, 46~48F ambient temp)

That matches exactly what I saw. The temps climb in the beginning but then actually keep dropping. There must be other things happening inside the battery that made Tesla decide to taper the power down regardless of temperature. One of their highest priority was longevity of the battery.

 

[apacheguy]

Well remember that the current taper algo on the 85s dates back 3 years. So, yeah, obviously they were being very cautious and did not want to impact long term battery health. I think now though Tesla should have sufficient data to know that they can relax the taper a bit.

 

[wk057]

The cells I've tested from the 85 packs can handle some pretty crazy charge rates. Even as high as 2C for a bit is possible.

The problem is thermal vs degradation vs cooling capacity. The cooling loop in the battery simply can't handle the heat generated in the cells during high speed charging. It mitigates it by slowing the increase, but it can't do that forever... hence the taper.

The supercharging curve is not a normal lithium-ion charging method. It's basically tailored to the pack's thermal properties with regard to cooling. I think the algorithm could use some tweaking to squeeze some slightly faster charges in some situations, but overall, I don't think it would make a lot of sense to change it substantially. Theoretically, they could hold the cell at a slightly higher temperature, and thus shift the taper, but that is a terrible idea with these cells from a degradation perspective. High temps are the biggest factor in degradation in my testing. The higher the temperature as the SoC rises, the more degradation.

I've only limited data on the 90 cells, but enough to see that internal resistance doesn't change as drastically during high C charging like in the 85 cells... thus less heat generated, thus faster charging would be possible.

Lots of other factors with supercharging, also. For example, the older non-motorized charge ports can't handle the high currents for as long as the newer ones without getting dangerously hot... and a good amount of 85's would have the older charge ports. (And the newer port can't really be retrofitted without changes to the body of the car... I tried. )

 

[David99]

Thanks Jason for the info. That explains why they let the temperature drop as the SoC gets higher. I never thought of the charge port being a limiting factor. That sucks. One way or another it seems though that Tesla has a rather rigid curve programmed rather than adjusting to real conditions. I noticed the charge rate and taper is the same weather I'm in the desert at 110 degree or in the winter at 14 degree.

 

[Canuck]

Lots of other factors with supercharging, also. For example, the older non-motorized charge ports can't handle the high currents for as long as the newer ones without getting dangerously hot... and a good amount of 85's would have the older charge ports. (And the newer port can't really be retrofitted without changes to the body of the car... I tried. )

Interesting! If an old 85 vs new (charge port doors) arrived at a Supercharger with say 10%, what is the difference in time to get to about 80%?

Maybe I don't want the answer given your... since I doubt it's insignificant.

 

[Zextraterrestrial]

can't retrofit a charge port .....but Autopilot retrofit /baffled/
most interesting

 

[apacheguy]

Interesting! If an old 85 vs new (charge port doors) arrived at a Supercharger with say 10%, what is the difference in time to get to about 80%?

Maybe I don't want the answer given your... since I doubt it's insignificant.

Pretty sure there would be none at all. I guess in theory Tesla could have a switch in the firmware that would detect the charge port capabilities and adjust to an appropriate taper, but based on what @wk057 said this is not how it's done. All 85s have the same taper curve regardless of charge port revision.

I think what they could do is have something like Intel Turbo Boost where the processor (in this case the battery) checks the thermal overhead and determines whether it is safe to sustain a faster rate. But I agree with @David99 in that the taper curve is rigid and is not flexible toward environmental factors. I've definitely supercharged before where it is obvious that the cooling loop is not running at 100% and in this case the pack could easily buffer the extra heat generated by faster charging.