5 ms·

You still need to convert this high supply voltage to a lower voltage to match the cell voltage for charging. The currents involved mean this converter is stil

by mbell 14y ago

You still need to convert this high supply voltage to a lower voltage to match the cell voltage for charging. The currents involved mean this converter is still likely to dissipate a lot of heat, even if it is extremely efficient.

lutusp 14y ago
> You still need to convert this high supply voltage to a lower voltage to match the cell voltage for charging. No, instead you charge the cells in series. That delivers the same power while avoiding the problem of having to produce overly high currents. > The currents involved mean this converter is still likely to dissipate a lot of heat, even if it is extremely efficient. Yes, but there are ways to minimize this loss factor. Obviously a fast-charging scheme for a car is going to involve a lot of current, but the system designers do all they can to minimize that current. The primary way they do that is by both charging and discharging the cells arranged as much in series as is practical. In the Tesla design, there are 11 modules connected in series and delivering 375 volts nominal (and requiring 375 volts to produce an optimal charging current). So there's no issue of changing individual cells at their normal cell voltage, instead the system charges modules consisting of 621 cells in an optimized series-parallel scheme: http://en.wikipedia.org/wiki/Tesla_Roadster#Battery_system http://en.wikipedia.org/wiki/Tesla_Roadster#Battery_system Quote: "Tesla Motors refers to the Roadster's battery pack as the Energy Storage System or ESS. The ESS contains 6,831 lithium ion cells arranged into 11 "sheets" connected in series; each sheet contains 9 "bricks" connected in series; each "brick" contains 69 cells connected in parallel (11S 9S 69P)"
- mbell 14y ago
  By 'cell' I meant the overall pack, not the individual unit within the pack. From your link: "A full recharge of the battery system requires 3½ hours using the High Power Connector which supplies 70 amp, 240 volt electricity" Multiply that current by 10-100 to 'charge it faster' and you have a huge problem with thermal dissipation, not to mention using truly massive cables.
  - lutusp 14y ago
    > Multiply that current by 10-100 to 'charge it faster' ... No, that can't be done without damaging the batteries. A fast charge in this context means multiplying the default charging current by roughly three, not 10, and certainly not 100.

by mbell 14y ago

lutusp 14y ago

> You still need to convert this high supply voltage to a lower voltage to match the cell voltage for charging. No, instead you charge the cells in series. That delivers the same power while avoiding the problem of having to produce overly high currents. > The currents involved mean this converter is still likely to dissipate a lot of heat, even if it is extremely efficient. Yes, but there are ways to minimize this loss factor. Obviously a fast-charging scheme for a car is going to involve a lot of current, but the system designers do all they can to minimize that current. The primary way they do that is by both charging and discharging the cells arranged as much in series as is practical. In the Tesla design, there are 11 modules connected in series and delivering 375 volts nominal (and requiring 375 volts to produce an optimal charging current). So there's no issue of changing individual cells at their normal cell voltage, instead the system charges modules consisting of 621 cells in an optimized series-parallel scheme: http://en.wikipedia.org/wiki/Tesla_Roadster#Battery_system http://en.wikipedia.org/wiki/Tesla_Roadster#Battery_system Quote: "Tesla Motors refers to the Roadster's battery pack as the Energy Storage System or ESS. The ESS contains 6,831 lithium ion cells arranged into 11 "sheets" connected in series; each sheet contains 9 "bricks" connected in series; each "brick" contains 69 cells connected in parallel (11S 9S 69P)"

mbell 14y ago
By 'cell' I meant the overall pack, not the individual unit within the pack. From your link: "A full recharge of the battery system requires 3½ hours using the High Power Connector which supplies 70 amp, 240 volt electricity" Multiply that current by 10-100 to 'charge it faster' and you have a huge problem with thermal dissipation, not to mention using truly massive cables.
- lutusp 14y ago
  > Multiply that current by 10-100 to 'charge it faster' ... No, that can't be done without damaging the batteries. A fast charge in this context means multiplying the default charging current by roughly three, not 10, and certainly not 100.