3 ms·
Tesla brakes are conventional. Yes, the driver has to push harder if the hydraulics fail, same as any car. There's nothing unique to the failure here, normal
by ajross 1y ago
Tesla brakes are conventional. Yes, the driver has to push harder if the hydraulics fail, same as any car. There's nothing unique to the failure here, normal cars run their boosters off of the power train too (via belts or vacuum usually, also some have 12V pumps and would be subject to exactly this kind failure).
As to whether the booster is run off of the 400V or 12V bus I don't actually know. My guess would be the latter, honestly, since the parts would be more generic. But in any case it probably doesn't matter if the main battery fails as the 12V battery is tiny and would probably not provide enough power to run the hydraulics without the DC/DC converter.
- waffletower 1y agoSeems really odd to me to have 400V brake regeneration and run the brake booster off of 12V, but quick searches don't reveal the answer for a Tesla or even a Prius.
- rconti 1y agoCommodity auto industry supply chain parts? 400v is probably way overkill, and dealing with it is more complicated and expensive?
- ajross 1y ago"Regenerative braking" is a feature implemented by the drive motor and controller, it's got nothing to to with the brakes. Again, Tesla brakes are very conventional hydraulic devices and they work (and fail) like brakes in any other car you're going to drive.
- Reason077 1y agoThe most recent Teslas (Model Y Juniper) have gotten a bit less conventional as they now have blended braking. ie: the brake pedal controls both regenerative and friction brakes, with the brake pedal "feel" effectively implemented by software.
- xxs 1y ago>12V battery is tiny and would probably not provide enough power LiFePO4 is capable of providing massive amounts of current for its size (way higher than a conventional acid one). 100A is not that high amount of current to run even with 4s4p setup. A 10kg battery would be beyond sufficient (should be able to fully power the brake system for 1h use). Note: jump on the brakes is expected to consume around 1200W
- Reason077 1y ago> "A 10kg battery would be beyond sufficient" I don't have the exact weight, but Tesla's LFP low-voltage batteries weigh far less than that. Around 2kg at a guess. Rating is 12.8V nominal, 12Ah, 153.6Wh. Not all that much bigger than a laptop battery!
- ajross 1y agoBecause it fundamentally is just a laptop battery. The job of the 12V bootstrap battery is to bring the main control hardware (not even the MCU, I don't think) online so that the DC/DC converter can power the 12V bus from the main battery. There are a few other systems that expect to be powered in the event of a main battery failure, like door locks and charging. But I really don't think hydraulics like power steering/braking are on that list. The fallback for hydraulic failure is manual pressure, just like it is on any car. It's a naturally redundant system.
- xxs 1y ago2kg would be a monster of a laptop battery of course, esp since it's regular Li-Ion (not the one w/ Fe/P). LiFePO4 should be ~150Wh/kg. So indeed, the battery is 'tiny', like 1kg only. Yet, it'd have no issue supplying the brakes - it's less than 10C discharge rate. LiFePO4 tends to have much higher discharge rate which is the important part not the total capacity. Either way, the battery is indeed 'tiny'
- op00to 1y agoLiFePO4 can't really be charged and don't like being discharged below freezing.