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Supercharging Speeds: Who, what, where, why, and when

wk057

Vendor & Senior Tinkerer
Feb 23, 2014
5,931
13,439
Hickory, NC, USA
Everyone's been asking me for details on supercharger speeds.

I think it's time to do an FAQ on this and break things down on the technical side.

Post your Model S/X supercharging questions below, and I'll update this top post with as many answers as possible. I'll also add in some additional ones.

(Hopefully can make this work with my TMC account as it sits.)

Keep non-supercharging related stuff out. No range loss stuff, lawsuit talk, NHTSA stuff, etc.

---------------------

Q/A: (Will sort these eventually. Don't worry if I skipped you, just getting simple stuff initially)

Is a kilowatt hour the same concept regardless of amps or voltage?

kWh is a measure of energy capacity. Some algebra:

kWh = Ah * nominal_voltage
Ah = kWh / nominal_voltage
nominal_voltage = kWh / Ah

(Ah = amp-hours)

kW is a measure of power. Specifically, kilojoules per second... where 1kJ = ~0.278 Wh.

kW = (volts * amps)/1000

So if you're charging at home on 240V at 40A, you're getting 9.6 kW of power into the charger (and some amount less than that into the battery after conversion losses). In 1 hour you'll have added 9.6kWh (minus losses) of energy into the battery pack.

For supercharging, the same applies. If you're getting 350V at 300A, that's 105 kW. Alternatively, you can algebra this to get amps from amps = (kW*1000 / volts).

Unfortunately Tesla hides this data on vehicles now, so you can't easily calculate current/voltage anymore without CAN tools.

For most electrical things, including batteries, things are limited by current, not by power. For supercharging, the peak is around ~375A for non-gen3 units... which means in practice most vehicles will never hit that 150kW mark.

---------------------

I have a late 2015 MS P90D. Mileage is low (20,000) battery pack is original and I get decent charging speeds (110 kW at 30% SoC). I read that some have reduced charging speeds, how can I prevent that from happening?

Buy a P100D.

Jokes aside, the early 90 packs are pretty horrible. Your low mileage is helping you, but you'll eventually get lower charge speeds the more the pack is used and/or supercharged. The chemistry of the early 90 packs is just really bad, degrading twice as fast or worse than 85 or 100 type packs (or late 90 packs that use 100-type cells).

In short, there's not much you can do except limit use and hope for the best.

---------------------

Do the cars have some way to monitor the temp of the inlet wiring from the charge port to the pack?

All cars with the automatic charge port have decent thermal sense at the port. Superchargers have sensors in the handle itself also. Older magnetic ports (2014 and older, some 2015) have only one thermal sensor and... well, it's pretty bad and no helpful.

The charge port and associated components are definitely a bottleneck for high current charging. They're original testing was for about 200A continuous, and they're now pushing 375A+ into them peak, which is pretty crazy.

In short, most likely cause of dipping from peak that doesn't fit with the battery's capability is thermals at the charge port either in the port, the handle, or the pins themselves.

---------------------

More soon as time permits.
 
Last edited:
Is a kilowatt hour the same concept regardless of amps or voltage? My Tesla home charger charges at 40 miles per hour. If I charge at a Chargepoint charger, at $.25 per KwH it won't matter how long it takes to get a KwH?

Yes. If you are billed by the kwh, that is a unit of capacity, not time, so it doesn't matter how long it takes to get a kwh.
 
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AustinP

Active Member
Apr 6, 2015
1,517
1,280
Belgium
My car seems to follow the empirical rule of thumb reported by others: kW+% around 100 up to 30% and raises gently to 110 above.
(these are not exact figures out of SMT, just what I saw on the MCU)
Some times I also would see a “super peak”, like 120+kW at very low SoC if warm, but this drops within a few seconds.

1618141391857.png


Has your tinkering allowed you to understand the algorithm dictating SuC speed on the 85 (and others) ?
Is it true that some are SuC nerfed, and other not? What triggers the nerfing/new curves ?

Thanks

Note: these are measures dating from... July 2020, not much driving requiring SuC since then for us.
 
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Yes. If you are billed by the kwh, that is a unit of capacity, not time, so it doesn't matter how long it takes to get a kwh.
Thank you beatle...that's what I was hoping. I have ordered a refresh Model X. Since I can charge it away from home for the same price per KwH as home, but put it on a hotel point charge card, it's a better deal than home charging...When/If I get the vehicle. I leave our Model S in the garage plugged in when not in use. The X will be my daily driver.
 
Do the cars have some way to monitor the temp of the inlet wiring from the charge port to the pack? Maybe indirectly by monitoring charge port temp? 18650 pack cars seem to have this little dip in the charge curve after taking in around ~10kwh at 145kw rate (Version 2 SuC). Eventually goes back up. Wondering what component might cause this typical current limit: charge handle, inlet port, car wiring, pack heat... Maybe different each time. Sometimes I can get another 10kwh at full rate by switching pedestals but sometimes the current limit follows the car.
 

aerodyne

Nose cone car in hand > 2 refresh orders?
Nov 19, 2018
4,390
7,398
Los Angeles
It has been reported by Tesla Bjorn that the reduced SuC speeds will occur after about 10000 KwH of DC charging, even on the M3.

However, many 85 packs have had the speeds reduced with much less SuC. In my case, only 30k miles and 2400 KwH lifetime per SMT. Before 2019, 30-80% was 30 min, now takes 45 min.

Question...are the 85 packs likely to see continued reduction in SuC speeds with increased SuC, or have we already been fully nerfed?
 
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- What happens in the cell chemistry that Supercharging must be throtteled over time?

- What happens if tesla didn't slow down Supercharging in that Update (or youre on old Firmware), Will it damage the Battery? What exactly will damage?

- Why did Tesla throttle all 85/70, no matter if there are 50k Miles or 200k Miles on it or DC charged very little?

- What was Tesla detecting in that "abucance of caution" Update that made them throttle the Supercharging Speed of the 85 abruptly ?

- 90 Packs had that 95kW Peak Reduction for Years (75 Packs had 82kW), that was removed by the "Holiday Update" -
What did Tesla find? May it thottle again to 95kW after some DC charging? Maybe some Fleet Testing to collect Data?

Thaks a lot, wk!
 

wk057

Vendor & Senior Tinkerer
Feb 23, 2014
5,931
13,439
Hickory, NC, USA
Added some replies to the first post. Keep an eye on that, as it's likely to get updated more frequently than my delayed posts here below.

If I didn't get to you or skipped you or whatever, no worries... will try to get to every supercharging (and probably charging in general) related question if I have an answer.
 
All cars with the automatic charge port have decent thermal sense at the port. Superchargers have sensors in the handle itself also. Older magnetic ports (2014 and older, some 2015) have only one thermal sensor and... well, it's pretty bad and no helpful.

The charge port and associated components are definitely a bottleneck for high current charging. They're original testing was for about 200A continuous, and they're now pushing 375A+ into them peak, which is pretty crazy.

In short, most likely cause of dipping from peak that doesn't fit with the battery's capability is thermals at the charge port either in the port, the handle, or the pins themselves.

Interesting. If you were to replace the charge port and wiring from early motorized ports to a newer revision such as the one in the 2020 vehicles, would you be able to speed up supercharging? Is it just a matter of temperature being lower due to higher gauge conductors or would you also need to update the software config so that the car knows it has a newer revision that can take more power?


Related question:
There is a trick to wrap the charge handle with a moist towel to increase supercharging speeds. Is this tricking the sensor and creating a dangerous situation? Or is it actually keeping the handle cooler, allowing for fast charging safely?
 
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There is a trick to wrap the charge handle with a moist towel to increase supercharging speeds. Is this tricking the sensor and creating a dangerous situation? Or is it actually keeping the handle cooler, allowing for fast charging safely?

This makes me wonder what the cabling and handle materials are actually rated for. Don't know the insulation type; EPDM maybe? Likely rated for much higher temps than what is comfortable for the hand so a towel is probably not endangering the cable integrity.
 

aerodyne

Nose cone car in hand > 2 refresh orders?
Nov 19, 2018
4,390
7,398
Los Angeles
It has been stated that it is a good idea to upload the latest updates for best pack health.

We can assume that Tesla has been busy with software improvements, and some may be beneficial, However, not all of them are pack centric, or even useful.

In today's news, here are two new voice commands. They actually work:


Given the above, how serious is Tesla in maintaining the health of our packs with appropriate updates?
 
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Reactions: SmartElectric
I’ve seen some arguments for putting a cold towel on the charge handle in the summer. Would be interesting to see the science behind anything that limits besides batteries themselves.
Interesting? I would like to see the science behind it as well :) And I am guessing you are talking about the earlier "not cooled" cables rather than the V3?
 

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