Will the car charge if it is started but not driven?
3 Answers
When the car is started but not driven, it will charge, but the charging effect is poor and it takes a long time to fully charge the battery. The instantaneous power consumption during car startup is relatively high, and it takes a long time to replenish the battery's power. If the car is not driven for a long time, you can disconnect the negative terminal of the battery to avoid battery drain. The functions of the battery are: 1. When starting the engine, the battery supplies power to the starting system, ignition system, and electronic fuel injection system; 2. When the engine is stopped or idling at low speed, it powers the car's electrical equipment; 3. When the generator's output is insufficient, it can assist in supplying power to the electrical equipment; 4. It mitigates voltage surges in the electrical system and protects the car's electronic devices; 5. It can store excess electricity generated by the alternator.
From my personal driving experience, it's true that a car can charge the battery when idling after starting, but the efficiency is really low. I specifically tested it with a multimeter - once the engine is running, the alternator starts working, and the battery voltage slowly rises from around 12V to 14V, which indicates charging. However, when my battery was low once, I tried charging it at idle for 30 minutes and found the charge gain was minimal. Later, driving just two kilometers actually charged it significantly more. A mechanic told me that the higher the engine RPM, the faster the charging speed. At idle, the alternator only runs at about 1,500 RPM, producing at most 10A current, which might not even offset the power consumption when running the AC. Moreover, prolonged idling for charging can damage the car - exhaust can pollute the catalytic converter and easily cause carbon buildup. If you really need to charge the battery, driving is definitely the better option.
Last time I heard a professional technician use a dining analogy to explain this: idling to charge after starting the engine is like sipping milk tea with a thin straw, while charging while driving is like gulping it down with a thick straw. Once the vehicle starts, the alternator rotates with the engine via the belt, generating electricity as long as the engine is running. The issue is that the maximum charging power at idle is only around 10A, whereas daily use of the air conditioning/headlights/seat heating consumes over 15A. Previously, my car battery was aging, and in winter, I idled with the heater on while waiting, only to find the battery charge decreasing instead—this was the reason. To protect the battery, idling to charge should only be used as an emergency measure for up to 20 minutes; to properly recharge, you need to drive around for a while.
