Some knowledge about automobile generator and battery

2020/11/05

The car battery charging problems can be summarized as follows, after understanding these, you will have a general understanding of the car's power generation, battery charging and power consumption.

1. The motor drives the generator to generate electricity

The car engine is not only used to drive the vehicle, but also to power many systems on the car. The engine crankshaft has two ends, one end is connected with the flywheel, which needs to be connected with the gearbox to drive the vehicle. The other end is output by crankshaft pulley to drive some accessory equipment. For example, the crankshaft pulley in the above figure drives the generator, compressor, power steering pump, cooling water pump and other parts through the belt to provide power for them. So as long as the engine is running, the generator can generate electricity and charge the battery.

2. The automobile generator can adjust the power generation

We all know that the principle of the generator is that the coil cuts the magnetic induction line to generate current, and the faster the coil speed, the greater the current and voltage. And the engine speed from the idle speed of several hundred to several thousand rpm, the span is very large, so there is a regulating device on the generator to ensure that the stable voltage can be output at different speeds, which is the voltage regulator. There is no permanent magnet in the automobile generator. It depends on the coil to generate the magnetic field. The rotor of the generator is the coil that generates the magnetic field. When the generator is running, the battery will first electrify the rotor coil (called excitation current) to generate magnetic field, and then when the rotor rotates, it will generate rotating magnetic field and generate induction electricity in the stator coil. When the engine speed increases and the voltage increases, the voltage regulator disconnects the rotor current, so that the rotor magnetic field gradually weakens and the voltage does not rise.

3. Cars use fuel as well as electricity

Some people think that the automobile generator is running with the engine, so it is always generating electricity, so it is not necessary to use it in vain. In fact, this idea is wrong. The automobile generator does rotate with the engine all the time, but the power generation can be adjusted. If the power consumption is less, the generator will generate less power. At this time, the running resistance of the generator is small and the fuel consumption is low. When the power consumption is large, the generator needs to increase the power generation. At this time, the coil magnetic field is strengthened, the output current is increased, and the rotational resistance of the engine is also increased. Of course, it will consume more fuel. The simplest example is to turn on the headlights when idling. Basically, the engine speed will fluctuate slightly. This is because turning on the headlights will increase the power consumption, which will increase the power generation of the generator, which will increase the burden of the engine, so that the speed will fluctuate.

4. The electricity from the generator is used in the operation of the car

Many people have this question: is the power consumed by the car running from the battery or the generator? In fact, the answer is very simple. As long as your vehicle's electrical system has not been modified, the power of the generator is used in the operation of the car. Because the output voltage of the generator is much higher than the battery voltage, other electrical appliances in the car and the battery belong to the load. The battery can not discharge even if it wants to discharge. Even if the battery is fully charged, it is equivalent to a large one It's just capacitance. Of course, the generator control system of some cars is relatively advanced, and it will judge whether the power of the generator or the battery is used according to the situation. For example, when the battery is fully charged, the generator will stop running and use the battery power, which can save fuel. When the battery power drops to a certain degree or the brake or engine brake is applied, the generator is started to charge the battery.

5. Battery voltage

Household cars are basically 12V electrical system. The battery is 12V, but the output voltage of generator is about 14.5V. According to the national standard, the output voltage of 12V generator should be 14.5V ± 0.25V. This is because the generator needs to charge the battery, so the voltage should be high. If the output voltage of generator is 12V, the battery can not be charged. Therefore, it is normal to measure the battery voltage at 14.5V ± 0.25V when the vehicle is running at idle speed. If the voltage is lower, it means that the performance of the generator will decline and the battery may suffer from power loss. If it is too high, it may burn out the electrical appliances. In order to ensure good starting performance, the voltage of the automobile battery should not be lower than 12.5V in the flameout state. If the voltage is lower than this value, it may lead to difficulty in starting. At this time, it means that the battery is insufficient and needs to be charged in time. If the voltage still fails to meet the requirements after charging, it means that the battery is no longer working.

6. How long can the car run to fill the battery

I don't think this topic is of practical significance, because the car battery does not need to be fully charged at any time, as long as it does not affect the starting and excessive discharge. Because the car only consumes the battery power at the moment of engine start-up, it will be charged all the time while driving, and the power consumed at the moment of starting can be replenished in five minutes, and the rest is earned. That is to say, as long as you don't drive for a short distance only for a few minutes every day, then you don't need to worry about the battery charging dissatisfaction. In my own experience, as long as the battery is not scrapped, nothing will happen It's a problem that can't be solved by idling for half an hour. Of course, it's not impossible to get accurate data. For example, when a car's generator is idling, the output current is 10a, and the battery capacity is 60 A. if the actual charging current is 6a, the charging time is 60 / 6 * 1.2 = 12 hours. Multiplying by 1.2 is to consider that the battery charging current cannot be fixed with the change of voltage. But this method is only a rough result.