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>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 con
by 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.
- Reason077 1y agoI don't doubt you could run into problems in extreme cold, but our Model Y SR (LFP pack) has been fine charging in -5C or so. The car is pretty good at managing thermals and making sure the battery doesn't get too cold.
- op00to 1y agoRight, you need a heater to keep things happy! I added a little heater to my LiFePO4 battery packs that live outside. It seems fine like that to take the edge off. Way better than exploding!