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One of my firefighter friends says they're a little fearful of using the jaws of life on electric vehicles since cutting through a high-voltage electrical cable

One of my firefighter friends says they're a little fearful of using the jaws of life on electric vehicles since cutting through a high-voltage electrical cable would be disastrous. Luckily there are so few models right now they can memorize no-go places, but obviously this can't be counted on forever.

LatteLazy 6y ago
Edit: Cell voltage in a tesla is only 4.1V max. But there are systems with up to 375 total so I guess it's a valid question, especially as company's (not tesla AFAIK?) start putting cells into the body to squeeze as many as possible in... Original question: Isn't it all low voltage?
- stickfigure 6y ago
  Maybe if you work for PG&E. The internet says Tesla packs are 350-375 volts. Definitely has the potential to ruin your day.
- xxpor 6y ago
  Superchargers charge at 480V max, which from my understanding go directly into the cells (there's two phases in lithium battery charging, constant current and constant voltage. I'm fairly certain the constant voltage is for when the battery is low) So technically not "high voltage" as defined by the NEC (that starts at 600V), but still plenty enough to kill you. Especially if you're wet.
  - function_seven 6y ago
    > (...I'm fairly certain the constant voltage is for when the battery is low) Backwards. When the cell is low, the charging is at a constant current. The current is limited to whatever is deemed safe for the battery. Once the battery has charged to 80% or so, then the voltage will have reached the top, and any attempt to maintain the current will over-volt the cells. So the current is allowed to taper off as the voltage is held constant. For a single cell, that means the charger will apply whatever voltage is needed to deliver, say, 1 amp. Then when the voltage hits the 4.2V ceiling, it will stay there as the current naturally decays. A 100% charge is declared when the current falls below some threshold, like 50mA.
    - xxpor 6y ago
      Yeah, that makes way more sense, thanks!
- _ph_ 6y ago
  Tesla battery packs connect like 96 cells in a row to achieve the desired voltage and then many rows wired in parallel for the current. As P=U*I, you have to use 400V to keep the motor current somwhat reasonable. Still, for the performance Model S, the current at which the pyrotechnical breakers cut in ist 1500A, which is beyond scary :).
- numpad0 6y ago
  HVs are typically 200V/200A ~50kW, Nissan Leaf, Tesla, other various BEVs are 400V/1-2kA ~500kW, except I think Porsche and NIO is 800V/0.5-1kA ~500kW, higher or lower within classes depending on models/generations. They always make it into parallel blocks of series cells that each has the nominal pack voltage. By the way you don’t want 3.7V/135kA cable running next to you!

LatteLazy 6y ago

Edit: Cell voltage in a tesla is only 4.1V max. But there are systems with up to 375 total so I guess it's a valid question, especially as company's (not tesla AFAIK?) start putting cells into the body to squeeze as many as possible in... Original question: Isn't it all low voltage?

stickfigure 6y ago
Maybe if you work for PG&E. The internet says Tesla packs are 350-375 volts. Definitely has the potential to ruin your day.
xxpor 6y ago
Superchargers charge at 480V max, which from my understanding go directly into the cells (there's two phases in lithium battery charging, constant current and constant voltage. I'm fairly certain the constant voltage is for when the battery is low) So technically not "high voltage" as defined by the NEC (that starts at 600V), but still plenty enough to kill you. Especially if you're wet.
- function_seven 6y ago
  > (...I'm fairly certain the constant voltage is for when the battery is low) Backwards. When the cell is low, the charging is at a constant current. The current is limited to whatever is deemed safe for the battery. Once the battery has charged to 80% or so, then the voltage will have reached the top, and any attempt to maintain the current will over-volt the cells. So the current is allowed to taper off as the voltage is held constant. For a single cell, that means the charger will apply whatever voltage is needed to deliver, say, 1 amp. Then when the voltage hits the 4.2V ceiling, it will stay there as the current naturally decays. A 100% charge is declared when the current falls below some threshold, like 50mA.
  - xxpor 6y ago
    Yeah, that makes way more sense, thanks!
_ph_ 6y ago
Tesla battery packs connect like 96 cells in a row to achieve the desired voltage and then many rows wired in parallel for the current. As P=U*I, you have to use 400V to keep the motor current somwhat reasonable. Still, for the performance Model S, the current at which the pyrotechnical breakers cut in ist 1500A, which is beyond scary :).
numpad0 6y ago
HVs are typically 200V/200A ~50kW, Nissan Leaf, Tesla, other various BEVs are 400V/1-2kA ~500kW, except I think Porsche and NIO is 800V/0.5-1kA ~500kW, higher or lower within classes depending on models/generations. They always make it into parallel blocks of series cells that each has the nominal pack voltage. By the way you don’t want 3.7V/135kA cable running next to you!