Each car owner asks himself what device is needed to measure battery capacity. The measurement of this value is often carried out during a routine maintenance, but it will be useful to learn how to determine it yourself.
Battery capacity meter
Battery capacity is a parameter that determines the amount of energy given off by a battery at a specific voltage in one hour. It is measured in A / h (Ampere per hour), and depends on the density of the electrolyte, which is determined by a special device - a hydrometer. When buying a new battery, all technical parameters are indicated by the manufacturer on the case. But this value can be determined by yourself. There are special devices and methods for this.
The easiest way is to take a special tester, for example, "Pendant". This is a modern instrument for measuring the capacity of a car battery, as well as its voltage. In this case, you will spend the minimum amount of time and get a reliable result. To check, it is necessary to connect the device to the battery terminals and within a few seconds it will determine not only the capacity, but also the battery voltage and the state of the plates. However, there are other methods for determining battery capacity.
The first method (classic)
For example, a multimeter can be used as a device for measuring the vehicle’s battery capacity, but you won’t get accurate readings with it. A prerequisite for this method (it is called the control discharge method) is a full battery charge. First you need to connect a powerful consumer to the battery (an ordinary 60W light bulb is quite suitable).
After that, it is necessary to assemble the circuit, which consists of a multimeter, battery, consumer, and apply a load. If the light bulb does not change its brightness within 2 minutes (otherwise the battery cannot be restored), we take the readings of the device at certain time intervals. As soon as the indicator falls below the standard battery voltage (under load it is 12V), its discharge will begin. Now, knowing the period of time that was required to completely empty the energy supply and the load current of the consumer, it is necessary to multiply these values. The product of these quantities is the real battery capacity. If the obtained values differ from the passport data in a smaller direction, battery replacement is necessary. This method makes it possible to determine the capacity of any battery. The disadvantage of this method is the high cost of time.
Second method
You can also use the method in which the battery is discharged through a resistor using a special circuit. Using a stopwatch, we determine the time spent on discharge. Since energy will be lost at a voltage within 1 Volt, we can easily determine the current strength using the formula I = UR, where I is the current strength, U is the voltage, R is the resistance. In this case, it is necessary to avoid a complete discharge of the battery using, for example, a special relay.
How to make a device yourself
If it is not possible to purchase a finished device, you can always assemble a device for measuring the battery capacity with your own hands.
To determine the degree of charge and battery capacity, you can use the load plug. There are many models of ready-made forks on sale, however, you can assemble it yourself. Next, one of the options is considered.
This model uses an extended scale, due to which high measurement accuracy is achieved. There is a built-in load resistance. The scale is divided into two ranges (0-10 V and 10-15 V), which gives an additional reduction in measurement error. The device also has a 3-volt scale and another output of the measuring device, making it possible to check individual battery banks. A scale of 15V is achieved by reducing the voltage on the diode and the zener diode. The current value of the device increases if the voltage value exceeds the zener diode opening level. When a voltage of the wrong polarity is applied, the diode performs the protective function.
In the diagram: R1- transfers the required current to the zener diode; R2 and R3 are resistors selected for the M3240 microammeter; R4 - determines the width of the narrow range of the scale; R5 - load resistance, activated by the toggle switch SB1.
The load current is determined by Ohm's law. The load resistance is taken into account.
AA battery capacity meter
The capacity of AA batteries is measured in mA / h (milliamps per hour). To measure such batteries, you can use special chargers that determine the current, voltage and battery capacity. An example of such a device is the AccuPower IQ3 battery capacity meter, which has a power supply with a voltage range of 100 to 240 volts. To measure, you need to insert the batteries into the device, and all the necessary parameters appear on the display.
Determining capacity using a charger
Also, the capacity can be determined using a conventional charger. Having determined the magnitude of the charge current (it is indicated in the characteristics of the device), it is necessary to fully charge the battery and detect the time spent on it. After, multiplying these two values, we obtain the approximate capacity.
More accurate readings can be obtained using another method for which you need a fully charged battery, stopwatch, multimeter and consumer (you can use, for example, a flashlight). We connect the consumer to the battery, and with the help of a multimeter we determine the current consumption (the less it is, the more reliable the results). We note the time during which the flashlight shone, and multiply the result by the current consumption.