Fig. 9.6. Measuring the battery voltage with a multimeter. If the voltage is below 12.5 V, the battery should be charged
2. After 4-5 minutes, measure the voltage between the battery terminals. Red wire with tester terminal (multimeter) connect to the positive terminal of the battery, black to the negative (Fig. 9.6). When measuring, all consumers must be switched off.
Fig. 9.7. The principle of connecting a multimeter when measuring current, voltage and resistance. Consumers are, for example, lamps, a starter or a radio
Fig. 9.8. Using a special tester, you can determine the battery condition by measuring its capacity. The measurement should not last longer than 10 seconds, since the battery is under a lot of load
Measuring voltage, current and resistance
If you want to check the health of your car's various electrical systems, you don't have to go to an electrician right away. There are many different devices on the market that you can use to check the condition of your electrical system yourself.
Tester with lamp (with needle contact). With its help you can check the presence of voltage in an electric circuit. The brighter the lamp burns, the higher the voltage.
The needle pierces the insulation of the wire being tested. The other terminal of the device on the wire is connected to the "ground" (car body).
Warning: The incandescent lamp tester consumes a lot of power, so it cannot be used to test electronic devices (for example, a controller). For this you need a voltage tester with an LED.
LED tester. Depending on the design, this device determines the presence of direct and alternating voltage within 6–700 V. Visually, the presence of voltage is determined by the lighting of the LED. Simple devices of this type are inexpensive.
Universal tester (multimeter)This device can measure voltage and current (constant and variable) and resistance. You can use inexpensive devices with a digital display. Such a device is usually powered by an autonomous battery.
Voltage measurement. In order to measure, for example, the voltage of the battery at idle, connect the negative terminal of the device to the negative terminal of the battery or attach it to the ground. Connect the positive terminal to the positive terminal of the battery or the wire being tested. If the device shows only 10.4 V, this indicates a short circuit in one of the battery cells. Also check the voltage of the battery when the starter is turned on; a value of less than 8 V indicates that there is something wrong with the battery.
Measuring current. To do this, you need to break the circuit and connect the device between the open contacts. When measuring, it will be enough to disconnect the contact connector and connect the wire between its two contacts.
Attention! Always remember the threshold values that your tester can measure. Very high currents flow on the contacts of such consumers as the starter, which can damage the device during measurement.
Measuring resistance. In this case, the tester checks whether the current passes through a particular wire or switch. If the current passes without obstruction, the resistance value will be zero. If there is a break somewhere, the resistance value will tend to infinity. In addition, you can find out what internal resistance a particular device has.
When measuring the resistance of a wire, its ends must be stripped and each connected to a different terminal of the device (Fig. 9.7). When setting measurement values, always start with the maximum value.
Measure the capacity of the battery (Fig. 9.8).
Battery condition according to hydrometer readings
Battery status according to multimeter readings
