4 ms·

From what I keep hearing, current EV acceleration is limited by the battery discharge rates. I haven't seen anyone talk about creating a multi-tiered (hybrid) b

From what I keep hearing, current EV acceleration is limited by the battery discharge rates. I haven't seen anyone talk about creating a multi-tiered (hybrid) battery. Have a comparatively small capacitor sit as a "battery cache" for short (5-10 second) bursts of acceleration, and let the battery be the slow but efficient & steady main energy store. This would mitigate many potential downsides to capacitors (e.g. cost, leakage, energy density, etc etc).

jhoechtl 7y ago
Sounds absolutely reasonable to me. Patent solution?
SECProto 7y ago
Modern EVs accelerate incredibly quickly. Tesla uses the 0-60 time as a main feature of their marketing. Once you have enough battery cells, a large power draw (acceleration) or power feed (charging, deceleration) becomes a very small amount of current for each cell.
djrogers 7y ago
> From what I keep hearing, current EV acceleration is limited by the battery discharge rates Acceleration today is mostly limited by available traction. It's not at all clear that a liveable car could get appreciably faster acceleration than we have today without a breakthrough in tire technology.
- flipflipper 7y ago
  Yep, and why every supercar's 0-60 time is limited to about ~2.6s these days. Also why tesla is claiming to be able to achieve <2.6s only with the cold gas thruster "SpaceX" package, they're no longer solely relying on the tire traction.
  - tigershark 7y ago
    No, tesla s with ludicrous mode is doing 0-60 in 2.28 today. The new roadster is aiming for 1.9 and probably less with the SpaceX package.
    - flipflipper 7y ago
      The exact number wasn't really the point + elon has a history of releasing high performance spec's before the actual technology is ready. Maybe they have special tires in the works, but the rubber that's on the market today can't do that
- etaioinshrdlu 7y ago
  Can't the tires just continue to get wider and wider until the rear tires are even about 4 ft wide? That should provide lots of traction.
  - culopatin 7y ago
    But friction is dependent on the pressure between the contact patches. More area of contact reduces the pressure per unit of area. So you’d need more pressure on said tires without augmenting mass (because then you’d need yet more friction to accelerate that mass, that’s why wings are a thing, more pressure on the tires without adding mass that you’d have to turn accelerate. Problem with wings is that they not only add drag but they are not affecting anything at launch. Maybe if you had a big electromagnet under the car and a steel path under the asphalt.
    - magicalhippo 7y ago
      Just pack a giant fan onto it, kinda like an up-side-down hovercraft.
      - LargoLasskhyfv 7y ago
        Why not going full hovercraft? Use the obsolete tire technology only for transition and slow speeds, thereby eliminating all that rubber dust!1!!
    - mox1 7y ago
      Some race cars [1] put fans under the cars, sucking upward. This effectively created a vacuum under the car and allowed it to stick to the road pretty well. It was more for cornering fast than straight-line acceleration. But modern race cars to use aerodynamic tricks to create downforce, but only to keep the car on the ground at high speeds. 1. https://jalopnik.com/brabham-bt46b-fan-car-making-lemonade-from-lemons-5442597 https://jalopnik.com/brabham-bt46b-fan-car-making-lemonade-f...
  - jacquesm 7y ago
    But you won't be turning that car around any time soon. The Flintstones notwithstanding it isn't particularly clever to have your tires run the width of the car because the inner and outer radius during a turn will cause the tire to wear rapidly. You could cut the width-of-your-car tire into a lot of slices I guess but that would be mechanically quite complex and you'd still have to drive it somehow.
- grecy 7y ago
  The new Tesla roadster coming soon(TM) does 0-60 mph in 1.9 seconds, and the quarter mile in 8.8, which is staggeringly fast even by ultra car standards. People that spend years and hundreds of thousands of dollars on their dedicated drag car never get that fast. I don't believe there's ever been a production car that runs in the nine second range, let alone into the eights. I believe with EVs, traction is not as much of an issue because the computer can adjust the torque output 1000 times per second, unlike an Internal Combustion Engine which takes eons to react and change it's power output. Obviously off the line it is, but certain as you get moving more you can dump a lot of torque into sticky rubber. Tesla are having a "battery day" soon, and I for one suspect their new batteries (maybe just for the new Roadster, maybe for all their cars) will be some kind of hybrid capacitor, or at least have some of their capacity does that way.
  - kevin_thibedeau 7y ago
    Nobody needs this performance in everyday life.
    - tachyonbeam 7y ago
      That's right, nobody really needs this, but the point of the Roadster V2 isn't to satisfy a need, it's to eradicate the perception that gasoline cars are better performing. By building a supercar that will humiliate all the Porsches and Ferraris, with no hope of gasoline cars remotely in the same price range ever being able to compete (unless they go hybrid?), Tesla will catch a lot of press. A new generation of kids will grow up with the clear perception that electric cars are superior technology. They will have Tesla Roaster posters on their walls instead of gasoline cars. The roaster is very much an expensive PR piece, but it will change the world and accelerate the transition to renewable energy in a meaningful way. Perception counts.
      - strbean 7y ago
        > Tesla Roaster posters Now I'm wondering what Elon will name his coffee roasting company.
leggomylibro 7y ago
I think that hybrid buses have been doing this for a long time. They have big supercapacitors on the roof which buffer the rapid charge from regenerative braking and use it to recharge the battery or provide energy for acceleration. The problem I've always seen with supercapacitors is that their leakage current usually seems to increase as their ESR drops. So as they gain the ability to charge/discharge quickly, they lose the ability to hold charge over time. I wonder if there are ways to mitigate that, but there are other problems like poor handling of high temperatures and mechanical vibrations / shocks; both are difficult tradeoffs for automotive parts. They are proven solutions for buffering energy in EVs, but it's harder to justify the cost/weight in light passenger vehicles. That's why hybrid solutions like this are exciting. These look cool - does anyone know if they have two or four dielectric layers? I can't quite tell from the article. IIRC Supercapacitors use four while traditional capacitors use two, and I feel like the self-discharge/ESR tradeoffs of supercapacitors might have a lot to do with the finnicky EDLC technology. If they've managed to make traditionally-structured capacitors with the Farad ratings of supercapacitors, that would be very cool.
jacquesm 7y ago
EV acceleration is not in any way a factor in normal traffic.
tigershark 7y ago
Why would you need 0-60 accelerations of less than 2.28 sec? And anyway the new roadster next year should do it in 1.9 sec.
pjc50 7y ago
Have a look at the Formula 1 "KERS" systems.
baybal2 7y ago
> limited by the battery discharge rates. Really only a problem for hybrids with only 8-16 cells. Power density of any serious EV battery pack is enough to melt car's motor.

jhoechtl 7y ago

Sounds absolutely reasonable to me. Patent solution?

SECProto 7y ago

Modern EVs accelerate incredibly quickly. Tesla uses the 0-60 time as a main feature of their marketing. Once you have enough battery cells, a large power draw (acceleration) or power feed (charging, deceleration) becomes a very small amount of current for each cell.

djrogers 7y ago

> From what I keep hearing, current EV acceleration is limited by the battery discharge rates Acceleration today is mostly limited by available traction. It's not at all clear that a liveable car could get appreciably faster acceleration than we have today without a breakthrough in tire technology.

flipflipper 7y ago
Yep, and why every supercar's 0-60 time is limited to about ~2.6s these days. Also why tesla is claiming to be able to achieve <2.6s only with the cold gas thruster "SpaceX" package, they're no longer solely relying on the tire traction.
- tigershark 7y ago
  No, tesla s with ludicrous mode is doing 0-60 in 2.28 today. The new roadster is aiming for 1.9 and probably less with the SpaceX package.
  - flipflipper 7y ago
    The exact number wasn't really the point + elon has a history of releasing high performance spec's before the actual technology is ready. Maybe they have special tires in the works, but the rubber that's on the market today can't do that
etaioinshrdlu 7y ago
Can't the tires just continue to get wider and wider until the rear tires are even about 4 ft wide? That should provide lots of traction.
- culopatin 7y ago
  But friction is dependent on the pressure between the contact patches. More area of contact reduces the pressure per unit of area. So you’d need more pressure on said tires without augmenting mass (because then you’d need yet more friction to accelerate that mass, that’s why wings are a thing, more pressure on the tires without adding mass that you’d have to turn accelerate. Problem with wings is that they not only add drag but they are not affecting anything at launch. Maybe if you had a big electromagnet under the car and a steel path under the asphalt.
  - magicalhippo 7y ago
    Just pack a giant fan onto it, kinda like an up-side-down hovercraft.
    - LargoLasskhyfv 7y ago
      Why not going full hovercraft? Use the obsolete tire technology only for transition and slow speeds, thereby eliminating all that rubber dust!1!!
  - mox1 7y ago
    Some race cars [1] put fans under the cars, sucking upward. This effectively created a vacuum under the car and allowed it to stick to the road pretty well. It was more for cornering fast than straight-line acceleration. But modern race cars to use aerodynamic tricks to create downforce, but only to keep the car on the ground at high speeds. 1. https://jalopnik.com/brabham-bt46b-fan-car-making-lemonade-from-lemons-5442597 https://jalopnik.com/brabham-bt46b-fan-car-making-lemonade-f...
- jacquesm 7y ago
  But you won't be turning that car around any time soon. The Flintstones notwithstanding it isn't particularly clever to have your tires run the width of the car because the inner and outer radius during a turn will cause the tire to wear rapidly. You could cut the width-of-your-car tire into a lot of slices I guess but that would be mechanically quite complex and you'd still have to drive it somehow.
grecy 7y ago
The new Tesla roadster coming soon(TM) does 0-60 mph in 1.9 seconds, and the quarter mile in 8.8, which is staggeringly fast even by ultra car standards. People that spend years and hundreds of thousands of dollars on their dedicated drag car never get that fast. I don't believe there's ever been a production car that runs in the nine second range, let alone into the eights. I believe with EVs, traction is not as much of an issue because the computer can adjust the torque output 1000 times per second, unlike an Internal Combustion Engine which takes eons to react and change it's power output. Obviously off the line it is, but certain as you get moving more you can dump a lot of torque into sticky rubber. Tesla are having a "battery day" soon, and I for one suspect their new batteries (maybe just for the new Roadster, maybe for all their cars) will be some kind of hybrid capacitor, or at least have some of their capacity does that way.
- kevin_thibedeau 7y ago
  Nobody needs this performance in everyday life.
  - tachyonbeam 7y ago
    That's right, nobody really needs this, but the point of the Roadster V2 isn't to satisfy a need, it's to eradicate the perception that gasoline cars are better performing. By building a supercar that will humiliate all the Porsches and Ferraris, with no hope of gasoline cars remotely in the same price range ever being able to compete (unless they go hybrid?), Tesla will catch a lot of press. A new generation of kids will grow up with the clear perception that electric cars are superior technology. They will have Tesla Roaster posters on their walls instead of gasoline cars. The roaster is very much an expensive PR piece, but it will change the world and accelerate the transition to renewable energy in a meaningful way. Perception counts.
    - strbean 7y ago
      > Tesla Roaster posters Now I'm wondering what Elon will name his coffee roasting company.

leggomylibro 7y ago

I think that hybrid buses have been doing this for a long time. They have big supercapacitors on the roof which buffer the rapid charge from regenerative braking and use it to recharge the battery or provide energy for acceleration. The problem I've always seen with supercapacitors is that their leakage current usually seems to increase as their ESR drops. So as they gain the ability to charge/discharge quickly, they lose the ability to hold charge over time. I wonder if there are ways to mitigate that, but there are other problems like poor handling of high temperatures and mechanical vibrations / shocks; both are difficult tradeoffs for automotive parts. They are proven solutions for buffering energy in EVs, but it's harder to justify the cost/weight in light passenger vehicles. That's why hybrid solutions like this are exciting. These look cool - does anyone know if they have two or four dielectric layers? I can't quite tell from the article. IIRC Supercapacitors use four while traditional capacitors use two, and I feel like the self-discharge/ESR tradeoffs of supercapacitors might have a lot to do with the finnicky EDLC technology. If they've managed to make traditionally-structured capacitors with the Farad ratings of supercapacitors, that would be very cool.

jacquesm 7y ago

EV acceleration is not in any way a factor in normal traffic.

tigershark 7y ago

Why would you need 0-60 accelerations of less than 2.28 sec? And anyway the new roadster next year should do it in 1.9 sec.

pjc50 7y ago

Have a look at the Formula 1 "KERS" systems.

baybal2 7y ago

> limited by the battery discharge rates. Really only a problem for hybrids with only 8-16 cells. Power density of any serious EV battery pack is enough to melt car's motor.