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Most EVs have a 12V lead acid battery for standby power and to buffer the 12V accessory system. The solenoids to the traction battery are open when parked and

by wffurr 2y ago

Most EVs have a 12V lead acid battery for standby power and to buffer the 12V accessory system. The solenoids to the traction battery are open when parked and the 12V battery closes them when the car is started. This does mean you might actually need a “jump start” for an EV if the 12V battery is drained, eg from leaving a light on or a fault in the 12V charging system.

Reason077 2y ago
Yes, EVs still have a 12V battery, but it’s not always lead acid. Tesla, for example, switched from lead acid to Li-ion 12V batteries in all their models several years ago. So have Porsche, even in combustion models I believe.
- philjohn 2y ago
  They are a lot more expensive though, at least aftermarket.
  - Reason077 2y ago
    Yes but you have to replace them much less often. Kind of like LED vs incandescent light bulbs.
    - philjohn 2y ago
      True - they're also lighter.
tzs 2y ago
I assume that jump starting an EV takes a lot less current than jump starting an ICE due to no need to crank an engine. I'd guess it just needs enough to power the control electronics and close the solenoids to the traction battery? That raises an interesting question: is the power requirement low enough that you could make a hand cranked EV jump starter?
- philjohn 2y ago
  You would be correct. It needs enough to open the contactors which allows the high voltage battery to send power via the inverter to charge the 12V My Lithium Ion jump pack is tiny, about the size of two iphones stacked on top of each other, and a single jump uses only a few %.
- ycombinatrix 2y ago
  Back to crank starting a car? We have come full circle.
marcosdumay 2y ago
That's because everything in a car is standardized into 12V, but the EV engine run on some hundreds of Volts. It would be dangerous to feed energy from the engine's battery into the rest of the car. As a sibling said, that doesn't require that you use a lead battery. The only requirement is that it's insulated from the main one.

by wffurr 2y ago

Reason077 2y ago

Yes, EVs still have a 12V battery, but it’s not always lead acid. Tesla, for example, switched from lead acid to Li-ion 12V batteries in all their models several years ago. So have Porsche, even in combustion models I believe.

philjohn 2y ago
They are a lot more expensive though, at least aftermarket.
- Reason077 2y ago
  Yes but you have to replace them much less often. Kind of like LED vs incandescent light bulbs.
  - philjohn 2y ago
    True - they're also lighter.

tzs 2y ago

I assume that jump starting an EV takes a lot less current than jump starting an ICE due to no need to crank an engine. I'd guess it just needs enough to power the control electronics and close the solenoids to the traction battery? That raises an interesting question: is the power requirement low enough that you could make a hand cranked EV jump starter?

philjohn 2y ago
You would be correct. It needs enough to open the contactors which allows the high voltage battery to send power via the inverter to charge the 12V My Lithium Ion jump pack is tiny, about the size of two iphones stacked on top of each other, and a single jump uses only a few %.
ycombinatrix 2y ago
Back to crank starting a car? We have come full circle.

marcosdumay 2y ago

That's because everything in a car is standardized into 12V, but the EV engine run on some hundreds of Volts. It would be dangerous to feed energy from the engine's battery into the rest of the car. As a sibling said, that doesn't require that you use a lead battery. The only requirement is that it's insulated from the main one.