Hacker News Reader

Comment by tbrownaw | Hacker News Reader

> Effectiveness of regenerative braking depends on having an extremely large battery that can sink enough current to stop the car. An EV can do that, hybrids at best help the brakes out some. You just can't charge the battery fast enough doing anything but a very slow rolling stop.

This seems a bit exaggerated. Staying regenerative-only does require sticking to about half or so of how fast I could stop, but so far that seems to work fine unless a light turns right in front of me or traffic acts up. Usually it says it gets high 90's or 100%, and it didn't go below 50% even when a stoplight did turn at exactly the wrong time. (2022 Ford Escape non-plug-in hybrid, recently bought used.)

View on HN

It's just that Tesla didn't spend skill points on brake blending tech unlockable. Some people confuse it as being a piece of technology of its own.

Every other EVs and HVs assign first half of brake pedal for regen and bottom half for mechanical brakes. Tesla uses bottom half of gas pedal for the same, which eliminates the need to accurately determine the appropriate pedal force that corresponds to intended braking force to be added up with regen to match intended deceleration. Mapping regen to gas is `set_motor_torque(1.25 * gas_pedal - 25);` and that's much simpler.

They didn't spend skill points because back when they did it they wanted to lean hard into the "oooh, fancy futuristic EV, look at this cool new driving experience" brand image. Same reason performance cars get loud exhausts even thought they could have quit ones with no decrease in performance.

This is something that's always baffled me about Teslas. I have a Prius, and regenerative breaking being tied to the break pedal is easy and intuitive. It also means I can easily lift my foot of the gas pedal to coast. IDK it just seems like a much better design to have one "stop" pedal and one "go" pedal, vs one "stop" pedal and one "go/stop" pedal.

Counterargument is that it's even easier to have only one pedal you use to accelerate and decelerate. Having owned a Prius and a Y, the Tesla is actually smoother to control, by a very significant margin. It's actually a superior way to drive, though it is surprising the first time you see it.

100% of possible system capacity to accept regenerative charge on a smaller battery system will be a smaller absolute number than 100% of possible on a larger battery. If you assume everything else is constant, motor, inverter, battery C-rating etc.

The manual says it's energy recovered (ie, not something relative to system capacity), and this seems consistent with the other indicator that shows instantaneous braking power with a distinction between what the regenerative system is doing vs what (if anything) the traditional brakes are doing.

which car? i think the number you're referring to is relative to electrical system capacity.

It's NOT relevant to overall (tyre, brake system & engine braking & regen braking) braking system performance since that's a dynamic value variable over many factors constantly.

I'm not sure what you're arguing here.

Bigger battery is more capacity sure. But their point was that even without a big battery they have enough capacity to get close to maximum effectiveness, contrary to ajross saying that a hybrid's capacity is "not really" effective and "at best" helps "some".

just mistaken about maximum effectiveness

braking system = circa 1G of deceleration possible (depending on tyres, coeff of friction, temperature, ... etc etc)

So max effectiveness is unreachable for any regen system on a consumer car hybrid or ev, by a factor of around 6x i believe?

With recognition of the mistaken framing (near max effectiveness) we're back to the larger ev pack has a greater ability to sink current, a larger ability to slow the vehicle than does a smaller battery (obvious considerations about inverter capability, wire gauge etc etc aside)

I think you might be using a very different definition of "effectiveness" than they are.

Their definition of effectiveness is the percentage of braking force that turns back into electricity and goes into the battery. If your regen system can only do .15G, but 90% of your braking is under .15G, then you'll have about 94% effectiveness by that definition. 94% is not max but it's near max.

It's not about what happens during peak braking, it's about what happens over entire drives.

And when they say "half or so of how fast I could stop" they're underestimating, that's a comparison to a normal but aggressive stop, not pushing the pedal into the ground.

I won't speak to your '22 Escape, but I've driven countless hybrids going back to a '04 Prius and none of them were brake-free in general use. EVs really are.

That's because the regenerative braking is applied on the brake pedal, not by lifting up the accelerator. My '14 Prius has a dashboard option to show how much of the regenerative breaking capacity is being used, and it's very easy to stay well below that limit by just gradually slowing down. The friction brakes are only really used when you suddenly stop, which is something you want to avoid anyway.

And when regenerative breaking is not enough, a series hybrid can still apply compression breaking, before resorting to brakes.

Reply on news.ycombinator.com