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Some technical background: in addition to the propulsion electrical system, the Tesla has a conventional 12V electrical system for running lights, radio, door l

by tlb 13y ago

Some technical background: in addition to the propulsion electrical system, the Tesla has a conventional 12V electrical system for running lights, radio, door locks, computers, etc. This system is always on, unlike the propulsion power which is disconnected by a relay when the car is off. The 12V system has a conventional lead-acid battery which is kept charged when the vehicle is running by an inverter running off the propulsion battery. Presumably, the 12v inverter failed in this story so the lead-acid battery ran down. You'd get results similar in a conventional car where the alternator failed: gradually dimming lights, then suddenly no engine power.

Tloewald 13y ago
Except the Tesla should be able to detect a failed inverter instantly. How would the conventional 12v battery failing cause a loss of engine power, and yet continue running the touchscreen and hazard lights for half an hour?
- tlb 13y ago
  Lights and touch screens will still mostly work on half their normal voltage, but the propulsion control system is fairly conservative. Rightly so. Trying to keep going on flickering power could cause the control DSPs to behave erratically. Indeed, you could imagine the system being able to give an earlier warning for this class of failure. Perhaps they'll be able to add it in a future software update.
- dangrossman 13y ago
  I've had this exact scenario happen on one of my previous cars. The alternator was somehow overcharging the battery. At some point, the battery acid would basically be boiling over (the battery case was physically bulging out), and no longer function at its job of carrying power to the rest of the electronics in the car. The throttle could no longer operate, so the car just stopped moving, spontaneously in the middle of the road I was driving on. No battery sensor would detect this as there was no voltage drop before the battery stopped functioning, and I could still run the radio and headlights for a couple minutes even though the car couldn't be moved. Replacing the battery didn't fix anything (the first shop I took it to didn't realize the battery wasn't the issue since the alternator was putting out power), replacing the alternator did.
  - weaksauce 13y ago
    It should be able to see that it was overcharging. Too high a voltage(>14 or 15 volts for a conventional 12V lead acid battery) or too high an amperage would indicate overcharging.
    - dangrossman 13y ago
      It's tricky. You don't necessarily have to exceed the voltage range that would normally be seen to overcharge the battery, just fail to regulate the output correctly. It's correct to provide a certain extra voltage/amps when the battery is not fully charged and you turn on headlights and fans; it's not correct to put out that same power 100% of the time. It's probably possible to build a sensor that tracks all this, but normal cars with the same 12V system don't have that sensor either. If the alternator goes the way mine did, you won't even see a battery indicator on the dash (even though it has such an indicator), you find out about it when your car stops moving in the middle of the road.
deleted 13y ago
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by tlb 13y ago

Tloewald 13y ago

Except the Tesla should be able to detect a failed inverter instantly. How would the conventional 12v battery failing cause a loss of engine power, and yet continue running the touchscreen and hazard lights for half an hour?

tlb 13y ago
Lights and touch screens will still mostly work on half their normal voltage, but the propulsion control system is fairly conservative. Rightly so. Trying to keep going on flickering power could cause the control DSPs to behave erratically. Indeed, you could imagine the system being able to give an earlier warning for this class of failure. Perhaps they'll be able to add it in a future software update.
dangrossman 13y ago
I've had this exact scenario happen on one of my previous cars. The alternator was somehow overcharging the battery. At some point, the battery acid would basically be boiling over (the battery case was physically bulging out), and no longer function at its job of carrying power to the rest of the electronics in the car. The throttle could no longer operate, so the car just stopped moving, spontaneously in the middle of the road I was driving on. No battery sensor would detect this as there was no voltage drop before the battery stopped functioning, and I could still run the radio and headlights for a couple minutes even though the car couldn't be moved. Replacing the battery didn't fix anything (the first shop I took it to didn't realize the battery wasn't the issue since the alternator was putting out power), replacing the alternator did.
- weaksauce 13y ago
  It should be able to see that it was overcharging. Too high a voltage(>14 or 15 volts for a conventional 12V lead acid battery) or too high an amperage would indicate overcharging.
  - dangrossman 13y ago
    It's tricky. You don't necessarily have to exceed the voltage range that would normally be seen to overcharge the battery, just fail to regulate the output correctly. It's correct to provide a certain extra voltage/amps when the battery is not fully charged and you turn on headlights and fans; it's not correct to put out that same power 100% of the time. It's probably possible to build a sensor that tracks all this, but normal cars with the same 12V system don't have that sensor either. If the alternator goes the way mine did, you won't even see a battery indicator on the dash (even though it has such an indicator), you find out about it when your car stops moving in the middle of the road.

deleted 13y ago

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