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Comment by toomuchtodo | Hacker News Reader

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).

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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?

Regen braking is noticeably less powerful when your battery is nearly full, and you have to manually use your friction brakes more. Sounds like it might be a safety issue, but in any scenario where you use regen brakes you have more than enough time to switch to physical brakes if you want to.

that's correct. You don't get one pedal braking if it's not charging.

I don't think the brake pedal was being used in this test, though.

My understanding is that above 95% SOC, even if you’re not using the brake, regen will not occur and an error is presented to the user notifying them about regen limits.

Sure, so the car stops charging and still won't waste/damage its brakes in the tow.

Teslas have no resistor banks?

A great omission.

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.

> Why would a resistor bank be better than mechanical brakes?

Resistors don't wear out like frictional brakes do.

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.

Electric braking has close to no wear, and much cheaper EVs use it.

A resistor bank with liquid cooling will be few kilogrammes at most.

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.

There's a free 1000+ lb steel heatsink - the chassis of the car.

It wouldn't be, all teslas already have liquid cooling.

Few kilogrammes at most.

It isn't worth the complexity for the rare cases when it might be useful. Even if you live at the top of a mountain, the easier solution is to just not charge to 100% to account for your "free" energy gains when leaving.

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