5 ms·

It will ultimately be limited by it's cooling, as all Teslas have been. Can it manage long, steep grades while towing? Downhill, ICE motors can be driven by the

by sawjet 7y ago

It will ultimately be limited by it's cooling, as all Teslas have been. Can it manage long, steep grades while towing? Downhill, ICE motors can be driven by the wheels to preserve both fuel and brakes.

kube-system 7y ago
If regenerative braking is good enough technology for trains, it ought to be good enough of a technology for a light truck. https://en.m.wikipedia.org/wiki/Dynamic_braking https://en.m.wikipedia.org/wiki/Dynamic_braking
- arghwhat 7y ago
  Note that trains are a very different scenario due to not being battery powered. Many (most?) trains dump excess charge into the grid, meaning that it has no limitations on brake power nor capacity. Battery-powered vehicles have to protect their battery, limiting brake power to keep the battery cool, and brake duration as it cannot overcharge the battery. To compete with a train, a battery powered vehicle would need to implement rheostatic braking (i.e. brake resistors). Of course, conventional engine braking is not worth comparing to any of this, but I thought it was important to emphasize that trains ≠ cars.
  - kube-system 7y ago
    Of course there are many differences between a train and a car. But the technology is exactly the same: apply an electrical load to a motor/generator and it will generate a braking force. The source of the load doesn’t really make a difference as long as it meets implementation requirements. (Perhaps maybe the most ironic way they could dump excess electricity could be by running the onboard air compressor — literally the same thing an ICE vehicle does to dump energy when engine braking: compressing air.) My point is that the technology is definitely a good fit for braking large loads.
    - arghwhat 7y ago
      Of course, except that normal cars have no component to dissipate the load. The battery is the only way, and it has significant limitations. A resonable auxillary air compressor won't make a difference. With a heavy trailer going down hill, you'd need to at least dissipate tens of kilowatts, maybe even touching triple digits if you also need to slow down. Nowhere to dissipate the power → no regenerative braking.
      - organsnyder 7y ago
        My PHEV minivan (Chrysler Pacifica) does close to 100 kW of regen in hard braking. I imagine the Cybertruck could easily double that, probably a lot more.
        arghwhat 7y ago
        Peak dissipation is not particularly interesting in this context.
        organsnyder 7y ago
        That current is charging the battery—not dissipation. I have no idea what kind of energy the friction brakes dissipate (that's not reported on the dash like regen braking is).
        arghwhat 7y ago
        From the perspective of braking a motor, charging a battery is just a way to dissipate energy. A bad one at that, considering that there must be ample room for charge, and the charge rate must be limited. Sports cars dissipate several hundred kilowatts in their friction brakes (for reference, the Porsche Taycan which can almost do with only regen braking can regen ~270kW). A hard-braking truck will exceed this significantly, but of course distributed over many more brake discs. However, for the trailer scenario, I assume that if you go up a certain slope using N kilowatt of propulsion to maintain a stable speed, you'd need somewhere in the ballpack of N/2 killowatt of braking power when going down during the full duration (unlike hard braking, which is only for a few seconds).
- deleted 7y ago
  [deleted]
arghwhat 7y ago
Engine braking with ICE is practical, but is pretty much pointless to compare with regenerative braking capabilities of an electric motor. Not only does regenerative braking recharge the battery, it is possible to apply entirely arbitrary reverse torque should need be, where an ICE has a pretty fixed resistance.
- bluedino 7y ago
  It's not very useful on gas engines but it is for diesel
- Goz3rr 7y ago
  >where an ICE has a pretty fixed resistance. That's what the gearbox is for
  - arghwhat 7y ago
    Apart from inertia on initial clutch-in, there are diminishing returns from increasing the gear ratio when it comes to compression losses.

by sawjet 7y ago

kube-system 7y ago

If regenerative braking is good enough technology for trains, it ought to be good enough of a technology for a light truck. https://en.m.wikipedia.org/wiki/Dynamic_braking https://en.m.wikipedia.org/wiki/Dynamic_braking

arghwhat 7y ago
Note that trains are a very different scenario due to not being battery powered. Many (most?) trains dump excess charge into the grid, meaning that it has no limitations on brake power nor capacity. Battery-powered vehicles have to protect their battery, limiting brake power to keep the battery cool, and brake duration as it cannot overcharge the battery. To compete with a train, a battery powered vehicle would need to implement rheostatic braking (i.e. brake resistors). Of course, conventional engine braking is not worth comparing to any of this, but I thought it was important to emphasize that trains ≠ cars.
- kube-system 7y ago
  Of course there are many differences between a train and a car. But the technology is exactly the same: apply an electrical load to a motor/generator and it will generate a braking force. The source of the load doesn’t really make a difference as long as it meets implementation requirements. (Perhaps maybe the most ironic way they could dump excess electricity could be by running the onboard air compressor — literally the same thing an ICE vehicle does to dump energy when engine braking: compressing air.) My point is that the technology is definitely a good fit for braking large loads.
  - arghwhat 7y ago
    Of course, except that normal cars have no component to dissipate the load. The battery is the only way, and it has significant limitations. A resonable auxillary air compressor won't make a difference. With a heavy trailer going down hill, you'd need to at least dissipate tens of kilowatts, maybe even touching triple digits if you also need to slow down. Nowhere to dissipate the power → no regenerative braking.
    - organsnyder 7y ago
      My PHEV minivan (Chrysler Pacifica) does close to 100 kW of regen in hard braking. I imagine the Cybertruck could easily double that, probably a lot more.
      - arghwhat 7y ago
        Peak dissipation is not particularly interesting in this context.
        organsnyder 7y ago
        That current is charging the battery—not dissipation. I have no idea what kind of energy the friction brakes dissipate (that's not reported on the dash like regen braking is).
        arghwhat 7y ago
        From the perspective of braking a motor, charging a battery is just a way to dissipate energy. A bad one at that, considering that there must be ample room for charge, and the charge rate must be limited. Sports cars dissipate several hundred kilowatts in their friction brakes (for reference, the Porsche Taycan which can almost do with only regen braking can regen ~270kW). A hard-braking truck will exceed this significantly, but of course distributed over many more brake discs. However, for the trailer scenario, I assume that if you go up a certain slope using N kilowatt of propulsion to maintain a stable speed, you'd need somewhere in the ballpack of N/2 killowatt of braking power when going down during the full duration (unlike hard braking, which is only for a few seconds).
deleted 7y ago
[deleted]

arghwhat 7y ago

Engine braking with ICE is practical, but is pretty much pointless to compare with regenerative braking capabilities of an electric motor. Not only does regenerative braking recharge the battery, it is possible to apply entirely arbitrary reverse torque should need be, where an ICE has a pretty fixed resistance.

bluedino 7y ago
It's not very useful on gas engines but it is for diesel
Goz3rr 7y ago
>where an ICE has a pretty fixed resistance. That's what the gearbox is for
- arghwhat 7y ago
  Apart from inertia on initial clutch-in, there are diminishing returns from increasing the gear ratio when it comes to compression losses.