Supercharging: Twice is nice

The car would require a larger wiring harness to deliver ~600A to the battery from the existing connector, and/or would require another connector.

Also, stepping up from 90 to 120kW seems to be coming close to what the battery can handle without degrading in the process. I know what you're thinking - "split" the battery in two partitions and charge each half at 120kW. It's just that then you're not charging av 85kWh battery but two 42.5kWh batteries (that can't handle 120kW). There is a reason the 85kWh can charge faster than the 60kWh, and the same reason why the 40kWh (at least the planned one) couldn't supercharge at all.

jeff_adams said:

That's interesting to know. Elon just said that all future Teslas will be able to use the superchargers. I guess that means that GenIII has to have at least a 60kWh battery?

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That's not what I read into it. What I read into it is that the chemistry will support (without absurd degradation) that rate of charge. It says nothing about battery capacity.

Edit: Well maybe not nothing. It suggests that the battery won't be something trivially small like 1kWh.

There is no technical reason why the 40 kWh battery could not be Supercharged. Nissan, Mitsubishi, and GM all offer DC fast charging on 16-24 kWh batteries (even less for the Mitsubishi Outlander PHEV, somewhere in the 5-12 kWh range). I suspect the reason that Tesla did not offer it would be that the number of Supercharging stations required would "increase with the square of the range reduction" (Elon - from today's supercharger Q&A). Probably other reasons as well, as speculated on in the 40 kWh thread.

Jeff's idea of two 120 plugs could work. Nothing would have to change about Tesla's current plug and socket. One could be installed in each taillight with the appropriate duplicate wiring to the battery (twin SuperCharger option). If two adjacent supercharger bays were available, just plug one into each charge port. The rest is "just software." The biggest issue would be the effect on battery life when charging at 4-5C. This is a fast, but very likely possible, charge rate. Many batteries can do 4-5C charging, and even much higher, today. The only question is what is the limit of the cells that Tesla is using.

This could easily be the "charge faster than a gas fill-up" technology. Not really faster in true mph, but with a little "Tesla math" the actual wait time for 0-50% SOC "Twin SuperCharge" could be the same as gas fill-up, counting the time to pay. There are multiple advantages to free Supercharging!

It would be really cool if this is the June 20 announcement.

GSP

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jeff_adams said:

That's interesting to know. Elon just said that all future Teslas will be able to use the superchargers. I guess that means that GenIII has to have at least a 60kWh battery?

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I think you are right. The small battery entry level Gen3 will have about 60 kWh. It could be a little less, as long as the range is 208 EPA miles, like the Model S. That way the planned supercharger spacing and number of locations will work for both cars.

GSP

My understanding is that the charging rate is limited by the battery chemistry and cooling so I'm somewhat doubtful that two Supercharger connections could be utilized to anything close to their full capacity.

OTOH, I've long been in favor of dual Level 2 charging connectors so you could plug one car with dual chargers into two 30A J1772 connectors simultaneously.

The SC limits the car to 120kW which means about 1.5 C. The 1.5 C limit probably is battery specific. The Gen 3 cars will limit the C rate of charge to the lower of 120kW or the limit for its battery. This is software controlled.

@GSP - I suggested something similar on the Tesla forum (5/22/13):


"Since we're brainstorming...

Split TM battery into 2 "banks" (like on my sailboat) with charge ports on both sides of MS. Redesign SC bays to have cables from both sides (similar to gas pump islands). Plug in both cables. Charging time halved.

Considering SC installed numbers are still low, changes could probably be made & implemented relatively soon. Hardware upgrades to MS not so quickly, but doable.
Anyone have any idea about impact on other MS electrical components?"

I assume the questions being raised here with this approach are 1) Will battery coolant be adequate at this level, and 2) will twin charging exceed battery limits. I don't know answers to either, but I figured it might when amperage was 90kW.

The idea of splitting batteries into two banks will not address any charging speed bottleneck at the battery. The peak charging speed of a battery scales by size, so if you split a battery into two, all you will end up with is two smaller batteries each with half the peak charging speed. Add them together and you end up with the same speed as charging one battery as a whole.

The two connector idea however would solve a bottleneck at the connector.

jeff_adams said:

Lots of hints about it seem to point to the demonstration having to do with charging or battery swapping (He said "there is a way to recharge faster than filling a tank of gas). There will be lots of crazy ideas about what he's going to do, so let me throw out another one for discussion.

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Going on a road trip with a gasoline car, you have to stop at a pump, wait 5 to 10 minutes while the car fills up, move to a parking spot, then go to the rest room and get something to eat.

With a Model S, you stop at a parking spot, plug in, go the the restroom and get something to eat. This is "...faster than filling a tank of gas[oline] (sic)". Nothing more to it.

GSP said:

There is no technical reason why the 40 kWh battery could not be Supercharged.

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Disagree completely. Been rehashed a dozen times. Not doing it again.

Ok so good discussion here guys. While I think the double connector idea won't happen since it would be a very clumsy design and not in line with the way Tesla operates, I think Jeff and GSP may be right that it is in fact a technical possibilty. So then I guess it boils down to where the bottleneck is: the battery pack or the connection to the battery pack? It's true that my MiEV with it's 16kWh battery can accept almost 50kW og charge rate for a period of time given optimal conditions. However, Mitsubishi does actually state that frequent CHAdeMO charging will degrade the battery (as are Nissan with the LEAF). Tesla has basically said that you can Supercharge all you want, it won't degrade the battery.

My belief on the matter is that with the current pack design and chemistry of the 85kWh battery it would probably be possible to charge it at 240kW from 0-50% SOC which corresponds to a C of 2.8. This would require a very large diameter cable and connector (somewhere around 700A?), or a complex design as suggested in the OP with dual charge ports and dual wiring to the battery (and a more complex controls system). Also, charging at those rates would probably be detrimental to the battery and Tesla want even Supercharging to be a "no brainer" and without worries for the customer - they don't want to go in to the whole "yes, you can supercharge but not more often than 4 times a month or 20 times per year, not when the temperature outside is above 28,5 celcius, no more than twice in a single day, etc. etc." and how this would or would not void your battery guarantee for example.

J in MN said:

Going on a road trip with a gasoline car, you have to stop at a pump, wait 5 to 10 minutes while the car fills up, move to a parking spot, then go to the rest room and get something to eat.

With a Model S, you stop at a parking spot, plug in, go the the restroom and get something to eat. This is "...faster than filling a tank of gas[oline] (sic)". Nothing more to it.

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I would grant you that can interpret Elon's tweet like that. You can't do that with Javier's comment:

"Charging technology is only going to improve with time. Charging times will decrease significantly and range will increase accordingly. In the very near future, the argument that internal combustion automobiles are more convenient than electric vehicles will be a moot point. You will be able to arrive at a charging station with an empty battery and drive off with a full charge faster than you can fill up a gas tank."

He's crystal clear regarding the time between arrival at the charging station to driving off, vs. filling up a gas tank. Add a slow payment process to the gas tank if you want, but that's it.