5 ms·

New, 800V, electric cars, will recharge in half the time

12 points by martincmartin 5y ago

iknowstuff 5y ago
That's not how it works.
- errantspark 5y ago
  Hm? Double the voltage means twice the wattage for the same amperage, i.e. the same copper requirements. If the constraint is heat that it is indeed how it works.
  - kumarvvr 5y ago
    Ultimately, charging current through each battery is what matters. Too high and you will reduce life of the battery. Best case scenario is to slow charge over a long time to increase battery life. How those 800 v translate into voltage and current through the batteries is the critical factor here.
    - rcxdude 5y ago
      Battery cells generally have a rating on their maximum charge and discharge rate which is specified as a time: 1C means the battery will charge in an hour, 0.5C means two hours and 2C means half an hour. The nice thing about this is that it then doesn't really matter how you arrange the cells into a battery (whether you put them in series for a high voltage or parallel for a high current): the maximum charge time will remain the same, assuming you don't introduce any bottlenecks. It also means that larger battery packs have a higher peak charging power. It's not very difficult with modern EV batteries for the charger connection itself to become that bottleneck: this is the kind of area where higher voltages will improve charging. Higher voltages are also beneficial for other reasons: it reduces the amount of copper and weight you need in the car, enables smaller and cheaper motor designs (though you need more gearing as the motor RPM will also increase), and as power electronic devices improve, allows more efficient and cheaper electronics. Higher current systems do not at all scale in the same way, since with higher current there's basically no way other than just adding more material to carry it, and all that material tends to be heavy and expensive copper (or aluminium). High voltage, on the other hand, is getting easier and easier to handle as technology progresses.
- chipsa 5y ago
  The relevant factor for 800v vs 400v isn't the current in the battery, but rather the current in the DCFC cable hooking to the car. We can't very effectively increase the amount of current, because the cable gets too heavy. So it increase charging speeds, we need to increase the power by increasing the voltage.
  - hulitu 5y ago
    The battery pack has a working voltage. If your charger has a different voltage you need to convert that voltage to battery pack levels. So going from 400 V to 800 V says little about efficiency.
    - chipsa 5y ago
      The 400V vs 800V is nominal voltage for both the output from the charger and the battery pack. There's some trickery I've heard about with switching half the pack from parallel with the other half to series while charging. But generally the voltage across the output from the pack will be equal to the voltage coming from the charger.
jet_32951 5y ago
Yoicks. Sure hope EMTs are being advised of these. Cutting through a HVDC line started getting attention when Priuses became common and here we go making things worse. It would be interesting if a resident EMT were to write at length about these hazards.
- chipsa 5y ago
  Most HVDC lines are not going near the passenger compartment at least now (you have it in the battery compartment, but those tend to be relatively well armored now). And 800 isn’t especially worse than 400 since you need to avoid it regardless, I think.
- eliaspro 5y ago
  EMTs are trained in how to deal with gasoline leakage in accidents, now they're being trained how to handle high voltage systems. EVs have dedicated points to safely disconnect the HV system to allow for safe rescue operations, cutting through the chassis, etc.
tamaharbor 5y ago
And the high voltage chargers and plugs will kill a lot of people.
- DarmokJalad1701 5y ago
  Are existing 480V systems killing many people? If it is as bad as you say, the current 480V Tesla supercharger network with nearly 27000+ connectors worldwide should've sure killed a whole bunch of people in the last 9 years. It's not like 480V is that much safer to the body than 800V ...
- rcxdude 5y ago
  There's not much difference between 400V and 800V in terms of deadliness. Both will kill you pretty damn quick, and the systems are designed to make it very difficult to come into contact with it.

12 points by martincmartin 5y ago

iknowstuff 5y ago

That's not how it works.

errantspark 5y ago
Hm? Double the voltage means twice the wattage for the same amperage, i.e. the same copper requirements. If the constraint is heat that it is indeed how it works.
- kumarvvr 5y ago
  Ultimately, charging current through each battery is what matters. Too high and you will reduce life of the battery. Best case scenario is to slow charge over a long time to increase battery life. How those 800 v translate into voltage and current through the batteries is the critical factor here.
  - rcxdude 5y ago
    Battery cells generally have a rating on their maximum charge and discharge rate which is specified as a time: 1C means the battery will charge in an hour, 0.5C means two hours and 2C means half an hour. The nice thing about this is that it then doesn't really matter how you arrange the cells into a battery (whether you put them in series for a high voltage or parallel for a high current): the maximum charge time will remain the same, assuming you don't introduce any bottlenecks. It also means that larger battery packs have a higher peak charging power. It's not very difficult with modern EV batteries for the charger connection itself to become that bottleneck: this is the kind of area where higher voltages will improve charging. Higher voltages are also beneficial for other reasons: it reduces the amount of copper and weight you need in the car, enables smaller and cheaper motor designs (though you need more gearing as the motor RPM will also increase), and as power electronic devices improve, allows more efficient and cheaper electronics. Higher current systems do not at all scale in the same way, since with higher current there's basically no way other than just adding more material to carry it, and all that material tends to be heavy and expensive copper (or aluminium). High voltage, on the other hand, is getting easier and easier to handle as technology progresses.
chipsa 5y ago
The relevant factor for 800v vs 400v isn't the current in the battery, but rather the current in the DCFC cable hooking to the car. We can't very effectively increase the amount of current, because the cable gets too heavy. So it increase charging speeds, we need to increase the power by increasing the voltage.
- hulitu 5y ago
  The battery pack has a working voltage. If your charger has a different voltage you need to convert that voltage to battery pack levels. So going from 400 V to 800 V says little about efficiency.
  - chipsa 5y ago
    The 400V vs 800V is nominal voltage for both the output from the charger and the battery pack. There's some trickery I've heard about with switching half the pack from parallel with the other half to series while charging. But generally the voltage across the output from the pack will be equal to the voltage coming from the charger.

jet_32951 5y ago

Yoicks. Sure hope EMTs are being advised of these. Cutting through a HVDC line started getting attention when Priuses became common and here we go making things worse. It would be interesting if a resident EMT were to write at length about these hazards.

chipsa 5y ago
Most HVDC lines are not going near the passenger compartment at least now (you have it in the battery compartment, but those tend to be relatively well armored now). And 800 isn’t especially worse than 400 since you need to avoid it regardless, I think.
eliaspro 5y ago
EMTs are trained in how to deal with gasoline leakage in accidents, now they're being trained how to handle high voltage systems. EVs have dedicated points to safely disconnect the HV system to allow for safe rescue operations, cutting through the chassis, etc.

tamaharbor 5y ago

And the high voltage chargers and plugs will kill a lot of people.

DarmokJalad1701 5y ago
Are existing 480V systems killing many people? If it is as bad as you say, the current 480V Tesla supercharger network with nearly 27000+ connectors worldwide should've sure killed a whole bunch of people in the last 9 years. It's not like 480V is that much safer to the body than 800V ...
rcxdude 5y ago
There's not much difference between 400V and 800V in terms of deadliness. Both will kill you pretty damn quick, and the systems are designed to make it very difficult to come into contact with it.