Reasons why lead-acid batteries cannot reach their designed service life

Abstract: The reasons why lead-acid batteries often fail to reach their designed service life are analyzed, and a new charger design principle is proposed.

Keywords: battery; battery charging and discharging; new charger

1 Introduction

Although today's lead-acid batteries have made great improvements in structural design and raw materials, and their performance has been greatly improved, many well-designed and well-made maintenance-free lead-acid batteries have a theoretical life of more than 15 to 20 years when used in floating charge, but there are probably very few batteries that can actually achieve such a life in use. Take the dry-charged low-maintenance starting lead-acid batteries widely used in cars and motorcycles as an example. The design service life is more than 4 to 5 years. Through investigation, it is found that few can reach the above level, and most of them die within a few months to a year. We believe that the reasons are as follows:

1) The design of the charging equipment is not perfect and it is not convenient to use.

2) The lead-acid battery is not recharged in time after discharge.

In particular, over-discharge can cause fatal damage to the battery.

3) The products of a few manufacturers are of poor quality and are sold as inferior products.

For the above reasons, we believe that 2) and 3) are technically easier to prevent and solve. Only 1) involves technical problems that are more difficult to solve. Below we will focus on the problems in this area.

2Battery charging technical requirements

The technical indicators of the lead-acid battery provided by the manufacturer to ensure the service life are given at an ambient temperature of 25°C. Since the voltage of a single lead-acid battery has the characteristic of decreasing by about 4mv for every 1°C increase in temperature, the floating charge voltage of a 12V battery composed of 6 single cells in series at 25°C is 13.5V; when the ambient temperature drops to 0°C, the floating charge voltage should be 14.1V; when the ambient temperature rises to 40°C, the floating charge voltage should be 13.14V. At the same time, the lead-acid battery has another characteristic. When the ambient temperature is constant, the charging voltage is 100mv higher than the required voltage, and the charging current will increase several times, which will cause thermal runaway and overcharge damage to the battery. When the charging voltage is 100mv lower than the required voltage, the battery will be undercharged and will also cause battery damage. In addition, the capacity of the lead-acid battery is also related to the temperature. For about every 1°C decrease in temperature, the capacity will decrease by 1%. Therefore, the manufacturer requires the users of the lead-acid battery to charge the battery in time after the battery discharges 50% of the rated capacity in summer and 25% in winter.

Obviously, the lead-acid batteries in daily use cannot be kept in an environment of 25℃ for a long time. There are temperature differences between morning, noon and evening in a day, not to mention the greater temperature differences in spring, summer, autumn and winter. Therefore, the various thyristor rectifier type, transformer step-down rectifier type, and general switch regulated power supply type lead-acid battery chargers currently used on the market cannot meet the strict technical requirements for supplementary charging of lead-acid batteries by charging the battery in a constant voltage or constant current manner. Looking at the methods used in the past to charge lead-acid batteries, and the lead-acid battery chargers developed based on these methods, it is not difficult to see that their technology is not perfect. Using these products to charge lead-acid batteries will inevitably directly affect the service life of lead-acid batteries. At the same time, these chargers also have problems such as narrow operating voltage adaptation range, large size, low efficiency, and poor safety factor.

Figure 1 Schematic diagram of the natural balance charging principle

3 Natural Balance Charger

In response to the common problems in lead-acid battery charging, Changsha Yuheng Electronics Co., Ltd. has conducted a long and in-depth study on lead-acid battery chargers. With its own unique methods and ingenious designs, it has produced a new series of charger products, which solves the complex technical problems in lead-acid battery charging. After years of experiments, it has been confirmed that the service life of lead-acid batteries has been greatly improved. (This technology has been patented)

Now let's briefly introduce a new method of battery charging - the natural balance charging method. What is the natural balance charging method for batteries? Please see the connection diagram of battery charging shown in Figure 1.

There are two power supplies EA and EB in Figure 1. When power supply EA and power supply EB are at the same ambient temperature, the positive poles are connected to the positive poles, and the negative poles are connected to the negative poles. In the closed circuit formed by them, there is the following relationship. If EA is higher than EB, EA will provide EB with a voltage of EA-EB=ΔE, and at the same time, it will provide a Δi current to flow and infuse the power supply EB according to the size of ΔE. When EB absorbs the Δi current provided by EA and makes EB rise to be completely equal to EA (in the battery, it is manifested as an increase in the battery terminal voltage and an increase in the charge storage capacity), power supply EA will stop providing current to power supply EB, that is, EA=EB, ΔE=0, Δi=0.

In the above description, we replace EB with the battery to be charged, and calculate the corresponding voltage of the battery at different discharge depths and ambient temperatures. EA is carefully designed to be a power supply that can automatically adjust the output voltage and current according to the battery charging balance requirements at different ambient temperatures, and is connected accordingly. In a completely ideal situation, the power supply EA can charge the battery according to the current that the battery can accept at any ambient temperature. After the battery is fully charged, ΔE=0, Δi=0, and the EA power supply will no longer consume power. After that, EA only provides tracking balance compensation for the charged battery as the ambient temperature changes. Since the entire process of battery charging is completely automatic, we call it the natural balance method.

The completely ideal situation of this method is: after the battery is fully charged, the voltage difference between EA and the charged battery EB is ΔE=0, and naturally Δi=0. Since EA has no power to supply the battery (EB), the battery electrolyte cannot boil, nor can the water in the electrolyte in the battery be decomposed, and it is even more impossible to increase the pressure and temperature in the battery, which would cause safety hazards. Therefore, this method provides the battery with neither overcharging nor undercharging the battery, but a more convenient, safer and more reliable charging.

From the above analysis, it is not difficult to see that this method is particularly suitable for maintenance charging of maintenance-free and low-maintenance lead-acid batteries, and is more suitable for daily maintenance charging of batteries used for intermittent discharge, which is beneficial to improving the reliability of batteries in daily use and increasing the service life of batteries.

Finally, the main technical indicators of an intelligent charger for motorcycle 12V lead-acid batteries developed according to the natural balance charging method are introduced:

1) Rechargeable battery 12V4~10Ah;

2) The input power is suitable for AC 100~240V and DC 120~370V;

3) Weight ≤ 100g; Volume 60mm×35mm×30mm;

4) Applicable ambient temperature: -10～45℃.

4 Conclusion

There are two reasons that affect the service life of lead-acid batteries:

1) Lead-acid batteries have stringent requirements on their charging equipment when the ambient temperature changes. Due to the design defects of charging equipment in the past, the normal service life of the battery was affected.

2) After the lead-acid battery is discharged, due to the inconvenience of using charging equipment in the past, users are unable to recharge the battery in time, which causes damage and greatly shortens the battery life.