Quote:
Originally Posted by zamler
The battery acts as a giant capacitor, without it you are feeding half wave AC into the system. The various electronics are protected and filtered as well, but that does not mean they can't be damaged. As for what voltages a car will function under, it's surprising how low the voltage has to go before the car won't run at all. I've seen cars run (although poorly) with about 8 volts. 18 volts is the upper end the car can tolerate without possible damage. Proper regulation is 13.8-14.2 Volts.
As for boosting a car with the engine running, it has risks. It can put maximum load on the alternator, and initially connecting the jumper cables can put voltage spikes into the system, which is very hard on electronics. The best way to boost a car is to connect with both cars not running, wait a few minutes, pull the cables, start the car, then reconnect the cables. This will put some charge into the dead battery, so when you connect things with the engine running, the load will not be so severe.
Another thing to remember is, a block heater will make a huge difference in getting a car started. Even with a 100% charged battery, in very cold weather the engine oil is getting close to a solid state, which means turning the engine over will put a huge strain on the battery. 100% synthetic oil is worth every cent in bitter cold weather, it flows better in extreme conditions.
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Batteries are not, and do not function, as capacitors. Capacitors block DC current at full charge, and then release their charge as the voltage across them drops. They, along with the battery, are in parallel with the alternator, not in series, which is what I think you are visualizing (that's how one would conclude a battery is functioning like a big capacitor).
All you people worried about voltage spikes have clearly not given any thought to the enormous electrical noise generated by your starter motor, which is a DC motor with enormous high current electromagnetic coils.
As I've already said, if voltage spikes and dirty voltage regulation were a concern for your vehicles electronics, simply starting your car each trip would be fatal.