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by itengelhardt
3141 days ago
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Initially ludicrous mode was not just a software update.
You could get it on your (already delivered) MS P90D, but had to bring it into service. They changed a fuse and activated ludicrous mode in software. Of course, today all Tesla P100D get built with that fuse already in place - so it's "just a software upgrade" today. There's quite a bit of electrical magic going on for a fuse to be able to handle insane current bursts while retaining a good response time in case of a catastrophic fault. |
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What's going on is that the current drawn while flooring a ludicrous vehicle is a largish fraction of the current that should cause an instantaneous fuse blow. A fuse that melts at a given temperature and heats up as I^2 R wasn't going to cut it. In the electrical distribution industry, you'd get a fancy circuit breaker with an electrical trip device and call it a day. This has two issues for Tesla. First, your average electrical trip device uses a current transformer, and those don't work for DC. Second, DC current is considerably harder to interrupt than AC, and the current the fuse needs to carry is in the kA range (I have no idea what the short circuit current is), so a circuit breaker would be rather large. Hence a fuse, with a little explosive inside, with an active circuit, presumably using a Hall effect sensor, the voltage drop across the fuse, or maybe just a reed switch.
(Hmm. It's nice when fuses and such don't need external power. I wonder if there's sufficient voltage drop across the fuse during a fault to power the circuit that blows the fuse? I bet there is. It could even be a very simple circuit like a Zener diode in series with a resistive heater that sets off the explosive.)