Knowledge analysis of car battery: secondary battery & "cascade utilization" value

Two questions: How to install secondary batteries on

cars? Can

auto batteries be used for electric vehicles after being eliminated? After winter

, there are many vehicles whose batteries are "unusable", and they may lose power in just a few days. It’s always too troublesome to merge the lines; therefore, some netizens asked whether they can install a secondary battery, or whether the car’s obsolete battery can be installed on an electric car. Do you think this can be done? The answer to

is definitely not recommended, because there is a difference in the actual capacity of the battery, and many problems may occur during actual use.

basic knowledge

battery connection method:

series boost

parallel expansion

Whether a car or an electric vehicle is equipped with a battery, the "parallel" method must be adopted; because the electronic equipment in the car or the motor of the electric vehicle are all fixed voltage standards, For example, if a 12V standard car is boosted in series to 24V, the equipment and fuse may be damaged (the higher the voltage, the stronger the output current). The

parallel connection method is to increase the capacity without changing the voltage. Most of the batteries used in cars are 12V-55Ah, with a capacity of about 0.66kwh; after being eliminated, it seems to be good for electric vehicles. Even if only half of the capacity is left, it is actually Many scooters have the same battery capacity, but the problems of reverse charging and overcharging cannot be overcome.

Knowledge point 1: After batteries or lithium batteries of different capacities are connected in parallel, "reverse charging" will occur during discharging; that is, batteries of small capacity are discharged first, and it is not that large capacity batteries output current through small batteries and the circuit. , But the large battery charges the small battery. The small battery in this state is easily damaged, so the car is not suitable for mixing new and old batteries with large capacity differences.

also has problems when used in electric vehicles, because these vehicles basically have undervoltage protection systems, that is, when the battery capacity is too low, the voltage will drop, and when the voltage is too low, it will limit the current output or not allow it to be used. Once the undervoltage protection is turned on, the battery packs connected in parallel will use the battery with the lowest voltage as a reference, and the large battery cannot be discharged at this time.

Knowledge point 2: After batteries of different capacities are connected in series, there will always be an "overcharge" problem during charging; for example, a small battery will be fully charged in advance. At this time, a large battery but not full, then the charger will use a large battery. The voltage standard decides to continue charging.

At this time, the small battery is already in the limit state, and the current continues to act on the positive electrode not only can not catalyze the reaction, but also will cause the battery to heat up! The minor standard is that it will damage the battery, and the serious one is overcharge and fire. Therefore, batteries eliminated by automobiles are not recommended to be used in electric vehicles. The type and parameters of the auxiliary battery should be exactly the same, and the actual capacity difference should not be too large.

Battery capacity problem

Question 1: Why does low temperature cause the battery capacity to decrease? The reason is that temperature will affect the electrolyte and active materials. Lead-acid batteries rely on the electrolyte to react with the electrode materials to generate current. Changes in performance will affect the discharge capacity. At the same time, the capacity of lithium batteries will also decrease in low temperature environments, which is an unsolvable problem.

Therefore, the battery compartment of electric vehicles should be kept warm in winter to prevent cold air from entering the battery compartment to a certain extent, and the battery life will be improved to a considerable extent.

Question 2: Why is the battery life so short? The reason is that the plate vulcanization problem occurs during the discharge process. The reaction of lead with sulfuric acid solution will produce lead sulfate crystals. Normal reaction materials can be decomposed during charging, but some crystals with too high hardness are difficult to decompose. This phenomenon occurs every time

discharges. As a result, the reducible lead element gradually decreases during the charging process, and the concentration of the electrolyte decreases linearly. At the same time, the crystal will also affect the discharge efficiency of the plate. The problems at the two positions are at the same time Increasing, the service life of the battery will inevitably be very short, one side is scrapped after about 350 full charge and discharge. (Loss of electricity will accelerate the plate vulcanization)

Question 3: Why is there a big difference in the battery life of the same car? This is not the uneven quality of the battery, but the result of different car habits. For example, after parking, I like to listen to music in the car and make a relatively loud sound; then the power consumption per hour may reach 200-400 watts, and the battery capacity is only 500 or 600 watts.

Then suppose every time you listen to a song for half an hour, evenContinuing for 3 to 5 days is equivalent to completely emptying the battery once, which is equal to about 100 emptying times per year, and the battery may lose electricity frequently if it lasts for three years. On the contrary, if there is no such habit of using a car, it may only be emptied once in half a month, and the service life has not been reached in ten years. Therefore, there are really some vehicles whose batteries can be used for more than ten years.

Summary: It is not recommended to use the battery that is out of the car for other purposes. It is a reasonable way to replace the battery with a new one.

If you want to install a secondary battery, you don’t need to choose an ordinary battery. At present, the most cost-effective is the lithium iron phosphate battery pack; refer to some lithium battery electric vehicles, the 48V-20Ah vehicle is only 2k more, using this battery Connect it in series and then connect it in parallel to 12V or 24V, keep or install the charging module; afterwards, the charging module is led out through the battery, such a battery pack can meet the parking power of the RV.

This article comes from the author of Autohome and does not represent the viewpoint of Autohome.