4 ms·

> if it’s ever about to reach the point that it’ll no longer be able to start your car, it’ll just turn itself off. Your lights will fade out and the radio will

> if it’s ever about to reach the point that it’ll no longer be able to start your car, it’ll just turn itself off. Your lights will fade out and the radio will go quiet — but once you turn the key, everything will spring right back to life, no jump start required. How does that work? If the battery stops providing current to prevent itself from being fully drained, you're not going to have power to the car's computers to actually start anything.

chrisBob 11y ago
And will I have to reset all of my radio stations every time I leave the dome light on? With a manual I would almost rather run the battery until it is nearly dead.
shabble 11y ago
One possibility: It will know when the internal batteries are running low (the internal charge/discharge monitor IC doing battery "gas gauge" measuring). It'll maintain a reserve of a few crank's worth of energy, and trigger shutdown before that's exhausted. It can also tell if the engine is running, because the alternator will be, and charging it. It can also monitor the active discharge current. If the battery is low and there's a small but fairly constant discharge, it's probably lights/radio, and a timeout of an hour might be reasonable. It could then either cut power completely, or regulate discharge current to a couple of milliamps or something, just enough to sense teh spike when the starter motor is switched in. At that point, it switches in the supercap or goes back to full power 12v mode, and the starter gets cranked. The only downside I can see is that fully isolating the battery may have side effects that upset the ECU, radio or immobiliser system (I recall our radio would go into 'presumed stolen' mode if fully disconnected and require a PIN to work properly, I have no idea if/how that happens in modern cars though) A "dead" lead-acid battery often isn't dead enough for that to happen, just htat it can't supply the ~200A that the starter requires to crank.
- blueintegral 11y ago
  Bingo.
- devicenull 11y ago
  Is the starter even going to crank before the computer is running? Old cars, sure I can see this working.

chrisBob 11y ago

And will I have to reset all of my radio stations every time I leave the dome light on? With a manual I would almost rather run the battery until it is nearly dead.

shabble 11y ago

One possibility: It will know when the internal batteries are running low (the internal charge/discharge monitor IC doing battery "gas gauge" measuring). It'll maintain a reserve of a few crank's worth of energy, and trigger shutdown before that's exhausted. It can also tell if the engine is running, because the alternator will be, and charging it. It can also monitor the active discharge current. If the battery is low and there's a small but fairly constant discharge, it's probably lights/radio, and a timeout of an hour might be reasonable. It could then either cut power completely, or regulate discharge current to a couple of milliamps or something, just enough to sense teh spike when the starter motor is switched in. At that point, it switches in the supercap or goes back to full power 12v mode, and the starter gets cranked. The only downside I can see is that fully isolating the battery may have side effects that upset the ECU, radio or immobiliser system (I recall our radio would go into 'presumed stolen' mode if fully disconnected and require a PIN to work properly, I have no idea if/how that happens in modern cars though) A "dead" lead-acid battery often isn't dead enough for that to happen, just htat it can't supply the ~200A that the starter requires to crank.

blueintegral 11y ago
Bingo.
devicenull 11y ago
Is the starter even going to crank before the computer is running? Old cars, sure I can see this working.