3 ms·

Yup, last I checked the P90DL was around 500kW(!) at peak, that's 1,250A @ 400V. Someone accidentally steps on the brake pedal while your near a HV line(400V c

Yup, last I checked the P90DL was around 500kW(!) at peak, that's 1,250A @ 400V. Someone accidentally steps on the brake pedal while your near a HV line(400V can jump a bit) to one of the two motors? Yikes.

mikeash 11y ago
The Ludicrous version was enabled by fancy computer-controlled pyrotechnic fuses, because traditional melty-wire fuses have trouble past about 1200A. I think the new ones are good for up to 1500A.
- vvanders 11y ago
  Yeah, I was being a tad conservative. Either way that's a hell of a lot of power. I'm surprised we haven't seen someone killed yet with a few of the battery pack teardowns that's happened.
  - mikeash 11y ago
    I think the (very small) mismatch between your numbers and the 1500A figure may be a partly due to power going beyond 500kW, and partly due to voltage sag when drawing that much current. In any case, I didn't even mean that to be a correction, just an interesting related note. As for people getting killed, I think the pack is hard enough to get into that people who don't know what they're doing are mostly discouraged before they get to the dangerous part. Maybe.
deleted 11y ago
[deleted]
makomk 11y ago
The Tesla has contactors in the battery that isolate the HV and a facility to lock them out - and they'd better be reliable even if someone accidentally steps on the brake pedal and the car's in pieces, because rescue workers have to rely on them in order to avoid electrocution when extracting people from crashed and mangled Teslas. Besides, a lot of the failures are in low-voltage systems like door handles that are covered by a much shorter warranty than the drivetrain and HV.
- mikeash 11y ago
  There are two wiring loops you can cut which will cut power to those contactors and isolate the battery. If the car is sufficiently mangled, the first responders' first order of business will be to cut those loops, which will render the car safe no matter what controls people activate. But if you haven't cut those loops and you're taking the car apart and haven't isolated things yourself, there's nothing preventing the car from closing those contactors and energizing the high-voltage system while you're elbow-deep in it.
- vvanders 11y ago
  Not quite... When you step on the brake(with weight in the seat) you can hear the HV contactor engage(it's a soft thunk). In the case of emergency workers there's one of 3 specific places they must cut through in order to close the contact, otherwise the car is live. I think the chances of some random joe forgetting to safe the system are higher(I'm just doing a door repair, I don't need to safe the system).
mrfusion 11y ago
A standard car weighs 4000 lbs, that's a lot of weight to crush you if it falls on you while you're working on it. People shouldn't be allowed to go under vehicles to repair them. In fact changing a tire with a jack is very dangerous too.
- vvanders 11y ago
  Oh come on now. Your car doesn't go from weighing light as a feather to 4000lbs at the speed of light when two pieces of metal that you can't see connect. There's a reason you should have a healthy respect of high voltage lines, there's no visual indicator that they are energized. At 400V anything that's unshielded will also jump a non-trivial distance.

mikeash 11y ago

The Ludicrous version was enabled by fancy computer-controlled pyrotechnic fuses, because traditional melty-wire fuses have trouble past about 1200A. I think the new ones are good for up to 1500A.

vvanders 11y ago
Yeah, I was being a tad conservative. Either way that's a hell of a lot of power. I'm surprised we haven't seen someone killed yet with a few of the battery pack teardowns that's happened.
- mikeash 11y ago
  I think the (very small) mismatch between your numbers and the 1500A figure may be a partly due to power going beyond 500kW, and partly due to voltage sag when drawing that much current. In any case, I didn't even mean that to be a correction, just an interesting related note. As for people getting killed, I think the pack is hard enough to get into that people who don't know what they're doing are mostly discouraged before they get to the dangerous part. Maybe.

deleted 11y ago

[deleted]

makomk 11y ago

The Tesla has contactors in the battery that isolate the HV and a facility to lock them out - and they'd better be reliable even if someone accidentally steps on the brake pedal and the car's in pieces, because rescue workers have to rely on them in order to avoid electrocution when extracting people from crashed and mangled Teslas. Besides, a lot of the failures are in low-voltage systems like door handles that are covered by a much shorter warranty than the drivetrain and HV.

mikeash 11y ago
There are two wiring loops you can cut which will cut power to those contactors and isolate the battery. If the car is sufficiently mangled, the first responders' first order of business will be to cut those loops, which will render the car safe no matter what controls people activate. But if you haven't cut those loops and you're taking the car apart and haven't isolated things yourself, there's nothing preventing the car from closing those contactors and energizing the high-voltage system while you're elbow-deep in it.
vvanders 11y ago
Not quite... When you step on the brake(with weight in the seat) you can hear the HV contactor engage(it's a soft thunk). In the case of emergency workers there's one of 3 specific places they must cut through in order to close the contact, otherwise the car is live. I think the chances of some random joe forgetting to safe the system are higher(I'm just doing a door repair, I don't need to safe the system).

mrfusion 11y ago

A standard car weighs 4000 lbs, that's a lot of weight to crush you if it falls on you while you're working on it. People shouldn't be allowed to go under vehicles to repair them. In fact changing a tire with a jack is very dangerous too.

vvanders 11y ago
Oh come on now. Your car doesn't go from weighing light as a feather to 4000lbs at the speed of light when two pieces of metal that you can't see connect. There's a reason you should have a healthy respect of high voltage lines, there's no visual indicator that they are energized. At 400V anything that's unshielded will also jump a non-trivial distance.