4 ms·

If they didn’t discharge, the frame of the car could be at 400-800 volts, making it hard to safely cut the frame to free someone from a bad wreck. These batter

If they didn’t discharge, the frame of the car could be at 400-800 volts, making it hard to safely cut the frame to free someone from a bad wreck. These batteries would be much more useful for electric bikes/mopeds/motorcycles as they don’t have the same safety complications cars do.

PeterisP 6y ago
And if they did discharge, then that would unavoidably cause a fire by releasing (i.e. dumping to waste heat) a huge amount of stored energy quickly.
ampdepolymerase 6y ago
Depends on the circuit. Most batteries' voltage are <5 volts in default configurations. You can move the voltage boost/serial circuitry segment to the engine area. It will waste a lot of material and create redundant wiring but the overall structural voltage will be low. Low voltage does not mean it would not catch fire however.
- extrapickles 6y ago
  High voltage battery packs are required due to the power required to move a car. A 50hp engine[1] needs ~37kW which at 5 volts, that is 7,500 amps of current, which requires comically large bus bars (~200x10mm) and conversion electronics. Even at 48 volts[2], you still need ~780 amps, which still requires very large conductors. At 400 volts, for the same motor, the wiring only needs to be sized for 100 amps, which is reasonably practical (think wire found on welders). [1]: Let assume that 50hp is the max required steady state output for a motor in a passenger car, and lets ignore any peak/dynamic loads and HVAC as this is napkin engineering [2]: 48v is generally accepted as the highest voltage before you really need to know what you are doing, though at these power levels, you still should know what you are doing as things like to weld, melt, become bad motors and/or explode.
  - ampdepolymerase 6y ago
    You are right. However, they do have the car's entire superstructure to work with.

PeterisP 6y ago

And if they did discharge, then that would unavoidably cause a fire by releasing (i.e. dumping to waste heat) a huge amount of stored energy quickly.

ampdepolymerase 6y ago

Depends on the circuit. Most batteries' voltage are <5 volts in default configurations. You can move the voltage boost/serial circuitry segment to the engine area. It will waste a lot of material and create redundant wiring but the overall structural voltage will be low. Low voltage does not mean it would not catch fire however.

extrapickles 6y ago
High voltage battery packs are required due to the power required to move a car. A 50hp engine[1] needs ~37kW which at 5 volts, that is 7,500 amps of current, which requires comically large bus bars (~200x10mm) and conversion electronics. Even at 48 volts[2], you still need ~780 amps, which still requires very large conductors. At 400 volts, for the same motor, the wiring only needs to be sized for 100 amps, which is reasonably practical (think wire found on welders). [1]: Let assume that 50hp is the max required steady state output for a motor in a passenger car, and lets ignore any peak/dynamic loads and HVAC as this is napkin engineering [2]: 48v is generally accepted as the highest voltage before you really need to know what you are doing, though at these power levels, you still should know what you are doing as things like to weld, melt, become bad motors and/or explode.
- ampdepolymerase 6y ago
  You are right. However, they do have the car's entire superstructure to work with.