321–330 of 399 posts
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Teslas have no resistor banks? A great omission.
A resistor bank of the required wattage would simply be a big lump of dead weight most of the time. And it would need its own cooling fan which would add even more weight.
Few kilogrammes at most.
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You can get this sort of benefit with a gas car with a manual transmission too. Engine braking uses no gas, its just your wheels turning your pistons and the friction from all of that slows the car down. Most of the time I only hit the brakes to go from 5mph-0mph in a manual car thanks to this.
This is commonly called power braking, usually called up in an emergency. It's a good technique that preserves handling. If you have RWD, your front suspension will remain more unsprung, in any case you can quickly apply the throttle to maneuver. The friction isn't what's working here, it is the compression of the cylinders in the engine draining momentum from the wheels, think of it as negative torque. As the forwar…
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Why would a resistor bank be better than mechanical brakes? Both get rid of excess power as heat, and you probably need the mechanical brakes anyway.
What is implied by the GP is that the cost of ownership for regenerative brakes is lower per joule. That's obviously true when that joule is "reused" and not so obvious when it's dissipated. Mechanical brake pads have to be replaced but I assume there is wear on the (more expensive?) parts in a regen system too.
A resistor bank with liquid cooling will be few kilogrammes at most.
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Teslas will switch to friction brakes when regeneration limits (peak current or battery SOC) are exceeded. I’ve sustained constant 50kw regen while downhill through Appalachia passes, no issues, with the caveat that regen current is limited if the pack is cold until it approaches operating temperature (yellow dashed lines on the regen current display indicate your reduced regen capability).
Does this mean that when the battery is full you must use the brake pedal? Or does the software automatically apply the friction brakes when you back off the accelerator?
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> However, towing for awhile ... is something that could presumably be done by just about any passing car A Tesla model 3 weighs over 4000 pounds. A base model Toyota Tacoma isn't even rated to tow that weight, there's no way any passing sedan could. Now remember that for regenerative _braking_ to work, the tesla's brakes have been on! Definitely not something any passing car can handle.
The weight of the Tesla is moot. The majority of the load experienced by the pulling vehicle is in the incredible drag of the Tesla’s wheels. They’re extremely difficult to spin and this for pace far exceeds any others that would normally be encountered when pulling a traditional load.
Having at least some regen braking all the time seems like kind of a benefit, since there's less risk of the rear car hitting the front car if the front car stops abruptly and the driver in back doesn't step on the brakes fast enough.
I can agree though that if the EV being towed really thinks it's supposed to try to stop as hard as it can, it would take a pretty powerful engine/motor or low gearing in the lead car to drag it along.
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I love this measure of charging speed. I'm wondering now why I haven't ever seen it used before.
It is getting more popular, also because vehicles charging at same energy input (say, 100 kW) can show larger kmh value (or mh) depending on how efficient the car is: the more efficient car can go further on the same energy input.
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The idea of pumped storage is pretty simple, but compared to lithium batteries the energy density is ridiculously small. If you already have an area that can be used for it (abandoned mine or reservoir) then it's pretty simply technology to build, but otherwise it's probably not worth it. As an example of how low density it is, imagine having a 1000l IBC tank, filled with water, on your roof at a height of 10m. That…
Density isn’t everything. It’s likely a lot cheaper and less environmentally destructive to dig a big hole in the ground than to manufacture a lithium battery.
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Sure, but it would be worth it. The cost is that you'd have to re-engineer maybe ten or twenty percent of major freeways and interstates (like have two miles of charging per every ten to twenty miles of regular road), and you'd need to establish a standard for trucks and passenger vehicles and get automakers to adopt it. (Or make it simple enough that it can be added as an aftermarket kit.) You'd also need to install…
> Sure, but it would be worth it. Are there really no better investments in electric than tearing up 17,000-35,000 miles of highway to make them slightly more efficient?
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> Most vehicles have virtually no braking power with the engine off You just need to press the brakes harder. Like 3 times harder, not 30. If you park in a slope and turn the engine off you can try braking after pumping the vacuum out - it works just fine.
If you’ve always used power assisted brakes and you’re not expecting to have to press really hard on the brakes it could easily lead you to rear end the car towing you if it stops suddenly. Also, without power assisted steering, modern cars are surprisingly difficult to control.