They aren't, really. They don't actually change gears, if you want to go backwards you spin the motor backwards.
Hilariously, jump starting EVs is a thing if the 12V battery dies. And no, you can't roll start them.
And no, you can’t roll start them.
I imagine you "can", it's just not very effective. Like, if they allowed you to switch it to regenerative breaking and let it roll down a hill. The problem is you can't get out any more energy than you put in. So if the battery is dead and you roll down the hill you won't be able to rull any farther up the other side than you started (even less when you factor in mechanical -> electrical -> mechanical. You'd probably better off putting it in neutral [if that's a thing for electric cars] and just let it roll)
No, you actually can't.
For safety reasons, the 400V main battery isn't hardwired to the car. There's a couple of contactors powered by the 12V battery that connect it to the car.
If your 12V battery dies, the contactors open and the car is completely dead. You have to jump it or replace the 12V battery, then the contactors pull in, then the main battery can start charging the 12V.
Even plugging it in doesn't work - the car won't take a charge if the electronics are dead.
If the main battery is dead but the 12V hasn't died yet, you can try regenning down a hill or plugging in or whatever. But if you lose the 12V, the car's bricked.
It's set up that way so that first responders can get to an accident, pop the hood, cut the 12V and then start cutting you out of the wreckage without worrying about high voltage cables.
just bridge them with a screw driver
Yeah, obviously there's technical reasons why. I was just approaching the problem theoretically. And then showing why the theory is stupid. It makes sense that they would implement other things for safety, especially if avoiding them only enabled a completely useless solution to a dead battery.
We just need to make all roads go downhill
Both ways.
Some have multiple speeds. I think the Porsche has 2 speeds for quick acceleration.
tl;dr: my PHEV does change gears when in EV mode, as weird as it sounds
So, I drive a Hyundai Ioniq Plug-in Hybrid EV (PHEV). It's a hybrid with a larger battery so you can plug it in and drive fully-EV on the battery for about 30 miles/50 kilometers or so. The freaky thing is that the EV motor is connected to the transmission, so it does switch gears sometimes and you can feel it when it does. Even freakier is that this also applies to regenerative braking: when you slow down from a high speed, you can sometimes feel it switching gears while you brake. That all isn't too bad since it's got a dual-clutch transmission and so it switches gears pretty quickly, but it can still be a bit freaky at times.
Additionally: there are some people who have converted antique cars to EVs, but to save money they didn't touch the transmission and instead elected only to replace the engine. They still have manual transmissions in them, though I suppose you could probably just find a suitable gear to leave them on 100% of them time. Still, you can, in principle, switch gears on them.
Typically I've seen people keep their car in 2nd (or reverse IIRC? That way your controller doesn't have to support reverse and you don't have to put in a new switch on the dash) in electric swaps. Also you don't use the clutch pedal to start, only to change gears, which is a bit freaky when you're not used to it.
On the highway there might be value in switching to a higher gear though, torque/efficiency curves aren't perfectly flat even on electric motors. I would be curious to know what gains would be had on a modern electric platform like an ID.3 if one was to put in a cheap two or three gears sequential/manual transmission (for all I know the efficiency gains would not offset the additional losses from the clutch and gearbox, and even if they are some gains I'm sure that they do not make up for the inconvenience/lack of comfort of a MT).
They aren't, really. They don't actually change gears, if you want to go backwards you spin the motor backwards.
Hilariously, jump starting EVs is a thing if the 12V battery dies. And no, you can't roll start them.
I imagine you "can", it's just not very effective. Like, if they allowed you to switch it to regenerative breaking and let it roll down a hill. The problem is you can't get out any more energy than you put in. So if the battery is dead and you roll down the hill you won't be able to rull any farther up the other side than you started (even less when you factor in mechanical -> electrical -> mechanical. You'd probably better off putting it in neutral [if that's a thing for electric cars] and just let it roll)
No, you actually can't.
For safety reasons, the 400V main battery isn't hardwired to the car. There's a couple of contactors powered by the 12V battery that connect it to the car.
If your 12V battery dies, the contactors open and the car is completely dead. You have to jump it or replace the 12V battery, then the contactors pull in, then the main battery can start charging the 12V.
Even plugging it in doesn't work - the car won't take a charge if the electronics are dead.
If the main battery is dead but the 12V hasn't died yet, you can try regenning down a hill or plugging in or whatever. But if you lose the 12V, the car's bricked.
It's set up that way so that first responders can get to an accident, pop the hood, cut the 12V and then start cutting you out of the wreckage without worrying about high voltage cables.
just bridge them with a screw driver
Yeah, obviously there's technical reasons why. I was just approaching the problem theoretically. And then showing why the theory is stupid. It makes sense that they would implement other things for safety, especially if avoiding them only enabled a completely useless solution to a dead battery.
We just need to make all roads go downhill
Both ways.
Some have multiple speeds. I think the Porsche has 2 speeds for quick acceleration.
tl;dr: my PHEV does change gears when in EV mode, as weird as it sounds
So, I drive a Hyundai Ioniq Plug-in Hybrid EV (PHEV). It's a hybrid with a larger battery so you can plug it in and drive fully-EV on the battery for about 30 miles/50 kilometers or so. The freaky thing is that the EV motor is connected to the transmission, so it does switch gears sometimes and you can feel it when it does. Even freakier is that this also applies to regenerative braking: when you slow down from a high speed, you can sometimes feel it switching gears while you brake. That all isn't too bad since it's got a dual-clutch transmission and so it switches gears pretty quickly, but it can still be a bit freaky at times.
Additionally: there are some people who have converted antique cars to EVs, but to save money they didn't touch the transmission and instead elected only to replace the engine. They still have manual transmissions in them, though I suppose you could probably just find a suitable gear to leave them on 100% of them time. Still, you can, in principle, switch gears on them.
Typically I've seen people keep their car in 2nd (or reverse IIRC? That way your controller doesn't have to support reverse and you don't have to put in a new switch on the dash) in electric swaps. Also you don't use the clutch pedal to start, only to change gears, which is a bit freaky when you're not used to it.
On the highway there might be value in switching to a higher gear though, torque/efficiency curves aren't perfectly flat even on electric motors. I would be curious to know what gains would be had on a modern electric platform like an ID.3 if one was to put in a cheap two or three gears sequential/manual transmission (for all I know the efficiency gains would not offset the additional losses from the clutch and gearbox, and even if they are some gains I'm sure that they do not make up for the inconvenience/lack of comfort of a MT).