[POLL] Would you prefer a bigger battery or less SuperCharger tapering?

[rdrcrmatt]

I'm surprised that it hasn't been stated yet in this thread...

The charing "taper" is something that happens as part of charging a Lithium battery.

In a lead acid 12v battery you just apply more than 12v to charge (typically 14'ish) and let'er rip. A Lithium battery needs to be charged in a different way (in short, voltage just over cell voltage until a point then "full" voltage as the battery gets fully charged).

Here's the kicker.. you can't just push more amps into the battery as it gets closer to fully charged. The "taper" you are talking about is due to the internal resistance of the battery increasing as the voltage comes up. "Pushing more amps" isn't possible. If you wanted to push more watts into the battery you'd have to do it at a higher voltage which would risk damaging the cells.

the only way to "reduce taper" would be to make a > 85kwhr battery and label it as 85kwhr.


TL,DR; You can't reduce the taper without either risking battery damage or using a larger battery.

 

[Yggdrasill]

TL,DR; You can't reduce the taper without either risking battery damage or using a larger battery.

Incorrect. You can decrease the internal resistance and increase the ability of the battery to accept current by tweaking the chemistry. Or you can switch to a completely different chemistry, like LTO, which can charge with 8-10C, and 0-80% takes ~6 minutes.

 

[clea]

you forgot a fourth option ... battery swapping.

 

[MartinAustin]

I voted for larger [capacity] batteries. It's cute that you have this poll and all, but the resulting data won't go anywhere or have any effect on Tesla's product plans. They're not going to change the tapering rate of the Superchargers. If there is any risk to the cars' batteries, they will eventually see a greater warranty claim issue re: their 8-year 80% capacity guarantee.

I think they are already charging cars' batteries as fast as they possibly can. Here is where JB Straubel discusses the issues:
Elon Musk Townhall meeting Amsterdam (HD): Firmware Version 6.0, SuperCharger Locations Europe, etc. - YouTube

Not trying to invalidate your question, but if you don't like tapering, don't stand there waiting while it does it. From flat, you get 80% charge in 40 minutes. Do you really need that extra 20% of charge? Where are you driving to? Is the last part of your journey that far from a Supercharger? Just drive to the next Supercharger.

With an 85kWh battery, the remaining 20% gets you about 50 miles (assuming some of the battery is kept for buffering etc.) and currently takes 35min to charge.
With a 110kWh battery, the remaining 20% would get you 70 miles (assuming some of the battery is kept for buffering etc.) and might take 45min to charge.

(my math could be flawed)

 

[widodh]

I voted for larger [capacity] batteries. It's cute that you have this poll and all, but the resulting data won't go anywhere or have any effect on Tesla's product plans. They're not going to change the tapering rate of the Superchargers. If there is any risk to the cars' batteries, they will eventually see a greater warranty claim issue re: their 8-year 80% capacity guarantee.

Oh, I don't have any expectations that they will change it for the current batteries.

But when chemistry changes come, what do you prefer? I bigger battery or less tampering at the SuperCharger?

The 85kWh is currently enough for me, but if it could SuperCharger quicker I'd be very pleased.

 

[Killface]

more Superchargers!

I originally voted for a bigger battery, but as always, I agree with Cottonwood.

I would love to have a 100-120kWh battery, but even more than that, I'd love to have superchargers every 80-90 miles on all major/medium highways.

 

[apacheguy]

Keep in mind that it's going to be quite a while before TM can sufficiently expand the SpC network to provide the spacing being requested here. It's nice to say we can use more superchargers because, heck, who wouldn't want that? But that's a long term strategy. Better tapering is something that can provide immediate relief to congestion at SpC and let owners get back on the road faster. It's the difference between something that can happen over the next year vs the next decade.

 

[AudubonB]

As long as we're discussing taking into account local considerations (a la Canada),

I'll have to suggest "A beefy-enough trailer hitch so as to be able to haul around a 500kWh-or-so battery bank so as to make travel here sorta-kinda practical".

'Cuz for the foreseeable future, the only way to get supercharged around Alaska appears to be by adding more pups to your dogsled team.

 

[rdrcrmatt]

Incorrect. You can decrease the internal resistance and increase the ability of the battery to accept current by tweaking the chemistry. Or you can switch to a completely different chemistry, like LTO, which can charge with 8-10C, and 0-80% takes ~6 minutes.

you're correct.. I assumed a constant chemistry.

This conversation is moot. We can't ask Tesla to increase the charge rate during the "taper".

 

[apacheguy]

This conversation is moot. We can't ask Tesla to increase the charge rate during the "taper".

IIRC, Elon mentioned an improved taper that never saw the light of day. What makes you so convinced that the taper curve is already at the physical limit of the pack?

 

[ItsNotAboutTheMoney]

That's what got me thinking as well. Model III will have a smaller battery (presumably), so you want them to charge fast.

Less queuing at the SuperChargers and shorter travel times.

I think it's a smart move of Tesla to have a 120/135kW SuperCharger already out there. A current Model S can't fully use it though, but future batteries probably will.

I'm actually of the opinion that for Gen 3 Tesla will stick close to a base size of 60kWh because they will want to keep making Supercharging faster to increase the capacity of the network at least cost to builder and that since the base size will be the most popular, improving tapering would have the biggest impact on charging. But, I'm rethinking. Since a Supercharger is actually a pair that theoretically can charge a pair of cars at constant total power, unless both cars have tapered to the point that the Supercharger is outputting less than its maximum output capability, better tapering might not make that much difference compared to increasing battery capacity in a sizable fraction of cars.

 

[widodh]

you're correct.. I assumed a constant chemistry.

This conversation is moot. We can't ask Tesla to increase the charge rate during the "taper".

Well, my point is. Do people want a bigger battery for more range? It seems so.

For me 85kWh is just fine, I just want to recharge faster at the SuperCharger.

I'm actually of the opinion that for Gen 3 Tesla will stick close to a base size of 60kWh because they will want to keep making Supercharging faster to increase the capacity of the network at least cost to builder and that since the base size will be the most popular, improving tapering would have the biggest impact on charging. But, I'm rethinking. Since a Supercharger is actually a pair that theoretically can charge a pair of cars at constant total power, unless both cars have tapered to the point that the Supercharger is outputting less than its maximum output capability, better tapering might not make that much difference compared to increasing battery capacity in a sizable fraction of cars.

50 or 60kWh is a good guess. I actually think that Model III will use slightly less energy so it can do with a smaller battery.

Charging at 1C is probably the goal. So a 120kW charger can charge two 60kWh batteries with 1C/60kW at a time.

 

[apacheguy]

Charging at 1C is probably the goal. So a 120kW charger can charge two 60kWh batteries with 1C/60kW at a time.

Hwo do you figure? Currently A batteries are the only ones to use a 1C max charge rate while the others support >= 1.75 C. Why would Tesla underrate the Model 3? Doesn't sound like something they'd do.

 

[widodh]

Hwo do you figure? Currently A batteries are the only ones to use a 1C max charge rate while the others support >= 1.75 C. Why would Tesla underrate the Model 3? Doesn't sound like something they'd do.

Oh, I meant as a overall average. So you start higher and taper down a bit and end up with 1C on average.

 

[cantdecide]

Given my driving history including a few dozen supercharging stops, a larger battery would make a significant difference, but reduced tapering would not. Considering my trips by length...

Under 300 miles... I currently supercharge near my destination from 10% to 40%. A bigger battery would save the need to charge, less tapering makes no difference as there currently isn't any tapering.
Over 300 miles... I need to stop to eat, diaper changes for kids etc... So my battery always fills regardless... So the bigger battery wins again.
Destination charging... Tapering is insignificant so the bigger battery wins.
Bigger batteries also win whenever you end up able to get free or cheap charging.

I know some people like to drive 6hours straight with no break. Not me or anyone in my family.

 

[republic]

Bigger battery, definitely. I need around 140kwh for my daily driving needs, and right now that means a midday run to the nearest supercharger.

 

[ThosEM]

We are on the horns of a dilemma here. There is no real escape from the taper without setting the battery on fire (AFIK), nor any way to fit a much bigger battery in the car. 90 and 100 are incremental changes from 85 kWh. Some are talking 130 kWh, but we aren't going to see 200-300 any time soon outside of heavy vehicles like transit buses or trucks.

One thing I have found to be helpful is to ALWAYS charge at your destination, even if it is only at 120V. Then, given an overnight or better, you avoid a stop early in your return trip and max out the first leg. So bring an extension cord and don't be shy about asking!

 

[FerraraZ]

I voted for more superchargers because I want EV's to be widely adopted. To do that, costs need to come down and if that means shipping a smaller battery on vehicles but more superchargers, that's my preferred way to go.

Not everyone can afford these vehicles. I want to see a 18k EV that can get a work commute down but would be required to charge more frequently for any real road trips. More superchargers will help this happen.

 

[apacheguy]

Hmm. Not sure about the battery catching fire part. If the cells get above 55 C, then yes I agree at 100+ kW it won't take too long before you'd get thermal runaway. Supercharging over the holidays though the compressor barely ran if at all and the battery temps were all less an 48 C. Under certain conditions, I'm convinced the taper is not thermally limited.

 

[mknox]

One thing I have found to be helpful is to ALWAYS charge at your destination, even if it is only at 120V. Then, given an overnight or better, you avoid a stop early in your return trip and max out the first leg. So bring an extension cord and don't be shy about asking!

Agree. When I drive to my daughter's place an hour or so northwest of Chicago, I try to top up at the closest Supercharger (Aurora, IL) so I can arrive as full as possible. I then plug in at 120 volts at her place and let the car trickle it's way back up to 90% before we depart. There are not a lot of Level 2 or 3 options near her house. When I leave, I can get as far as St. Joseph MI or Mishawaka, IN (depending on my route) on the way back to Toronto.