3 ms·

For a capacitor to be used in charging that way it would have to have something like the same capacity as the car's battery. Supercapacitors tend to have lower

For a capacitor to be used in charging that way it would have to have something like the same capacity as the car's battery. Supercapacitors tend to have lower specific energy density than batteries do so this would require reducing the car's range by something like a factor of 5. A capacitor much smaller than the batteries acting as a buffer for rapid acceleration and braking might make sense, though.

briffle 8y ago
I could see it used for the superChargers, so they could have more chargers feeding off a smaller power connection. (especially for the ones needed for the semi).
- newnewpdro 8y ago
  This is far more plausible, where space is abundant outside the vehicle to keep a cache of supercaps to charge from. Especially if the usage pattern tends to be very bursty. But if the superchargers are (or will be) continuously near 100% utilization it's pointless, they'll need the current at the mains.
- extrapickles 8y ago
  I doubt they will be used for either side of charging. Super/Ultra capacitors cost a lot more than batteries per watt hour.
  - hinkley 8y ago
    Why not in the charge control circuitry in the supercharger? Don’t those use some pretty big caps?
  - jws 8y ago
    In the context of a Supercharger the critical metric would probably be cost per charge/discharge cycle for a given capacity bank. While a car probable averages a fraction of a charge cycle per day, a busy supercharger might be on the order 10 cycles per day. Super capacitors degrade more slowly than batteries with cycles. The use which might make sense is to use the capacitors to supplement the grid supplied power during the initial fast charge phase, then in the slower final charging phases or idle time recharge the capacitors from the grid for the next customer. This levels out the demands on the grid and can result in a lower electricity rate from the power company. It all depends on the constants if it makes sense. Or maybe it doesn't make sense and Tesla needed something out of Maxwell's patent portfolio.
stcredzero 8y ago
For a capacitor to be used in charging that way it would have to have something like the same capacity as the car's battery. Supercapacitors tend to have lower specific energy density than batteries I was under the misapprehension that they had a much larger energy density. However, my next thought is that not all charging is the same. Only the 1st 60% of a charge is in the constant current part of the charge curve. After that, the charge rate falls off. Charging the last 10% of a battery's capacity takes much longer. What if the supercapacitor bank had about 10% of the capacity of the battery? That would still be a large increase in the size and weight taken up by energy storage, though. It looks like just putting more batteries in the car is the economical thing to do.
- hinkley 8y ago
  You could go other ways and downsize the battery a little bit, or tweak the definition of 100% and 0% (they play with those to keep the batteries from damaging themselves.)
- Symmetry 8y ago
  In general capacitors have much higher power density but much lower energy densities than batteries and supercapacitors are somewhere in between. http://large.stanford.edu/courses/2012/ph240/aslani1/ http://large.stanford.edu/courses/2012/ph240/aslani1/ Using a capacitor for the last 10% might make sense, or it might not. It's all about the specific numbers. It might be that a larger battery charged up to 90% might be better than a slightly smaller battery charged to 100% with the assistance of a capacitor. If you're adding a capacitor for power reasons anyways this might be a way to get more use out of it.

For a capacitor to be used in charging that way it would have to have something like the same capacity as the car's battery. Supercapacitors tend to have lower specific energy density than batteries do so this would require reducing the car's range by something like a factor of 5. A capacitor much smaller than the batteries acting as a buffer for rapid acceleration and braking might make sense, though.

briffle 8y ago

I could see it used for the superChargers, so they could have more chargers feeding off a smaller power connection. (especially for the ones needed for the semi).

newnewpdro 8y ago
This is far more plausible, where space is abundant outside the vehicle to keep a cache of supercaps to charge from. Especially if the usage pattern tends to be very bursty. But if the superchargers are (or will be) continuously near 100% utilization it's pointless, they'll need the current at the mains.
extrapickles 8y ago
I doubt they will be used for either side of charging. Super/Ultra capacitors cost a lot more than batteries per watt hour.
- hinkley 8y ago
  Why not in the charge control circuitry in the supercharger? Don’t those use some pretty big caps?
- jws 8y ago
  In the context of a Supercharger the critical metric would probably be cost per charge/discharge cycle for a given capacity bank. While a car probable averages a fraction of a charge cycle per day, a busy supercharger might be on the order 10 cycles per day. Super capacitors degrade more slowly than batteries with cycles. The use which might make sense is to use the capacitors to supplement the grid supplied power during the initial fast charge phase, then in the slower final charging phases or idle time recharge the capacitors from the grid for the next customer. This levels out the demands on the grid and can result in a lower electricity rate from the power company. It all depends on the constants if it makes sense. Or maybe it doesn't make sense and Tesla needed something out of Maxwell's patent portfolio.

stcredzero 8y ago

For a capacitor to be used in charging that way it would have to have something like the same capacity as the car's battery. Supercapacitors tend to have lower specific energy density than batteries I was under the misapprehension that they had a much larger energy density. However, my next thought is that not all charging is the same. Only the 1st 60% of a charge is in the constant current part of the charge curve. After that, the charge rate falls off. Charging the last 10% of a battery's capacity takes much longer. What if the supercapacitor bank had about 10% of the capacity of the battery? That would still be a large increase in the size and weight taken up by energy storage, though. It looks like just putting more batteries in the car is the economical thing to do.

hinkley 8y ago
You could go other ways and downsize the battery a little bit, or tweak the definition of 100% and 0% (they play with those to keep the batteries from damaging themselves.)
Symmetry 8y ago
In general capacitors have much higher power density but much lower energy densities than batteries and supercapacitors are somewhere in between. http://large.stanford.edu/courses/2012/ph240/aslani1/ http://large.stanford.edu/courses/2012/ph240/aslani1/ Using a capacitor for the last 10% might make sense, or it might not. It's all about the specific numbers. It might be that a larger battery charged up to 90% might be better than a slightly smaller battery charged to 100% with the assistance of a capacitor. If you're adding a capacitor for power reasons anyways this might be a way to get more use out of it.