We tell and show how, using ordinary digital multimeter You can measure the voltage of a car battery in different operating modes and thereby evaluate its performance. We will test a new battery with a capacity of 95 A/h. Voltage measurements are carried out using an inexpensive budget digital tester.
Checking the battery with a multimeter
The first measurement is carried out without connecting the battery to the load. In our case, this is the vehicle’s on-board network. Switch multimeter set to measure direct voltage with a limit of 20 V. Connect the probes of the device to the battery terminals. The device shows a voltage of 12.83 V. These readings correspond to a fully charged, working power source. For a working battery, a small spread of this parameter is allowed within the range of 12.4 - 12.9 Volts. If the battery voltage is 0.1 V less than the lower limit, then the battery charge is 10% less than the nominal charge. If by 0.2 V, then the undercharge will be 20%. Etc.
Let's move on to the next dimension. Now the battery terminals are connected to the vehicle’s on-board network. Even when the ignition is not turned on, there are active loads in the vehicle network.This is, for example, a radio, alarm, engine control unit. Due to the connected load, the voltage at the terminals has decreased. In this case, the battery produces a voltage of 12.58 V, which is what we see on the device display.
We will carry out the next measurement with the car running. When starting the engine from the starter, the voltage should not fall below 9 V. Then it will begin to rise when the generator comes into action. And ultimately it will increase to 13 volts or more, depending on the performance of the generator and voltage regulator.
We fix the probes of the device on the battery, record the readings again multimeter. The display reads 12.48 V. Start the engine. When the ignition is turned on, the voltage drops to 11.75 V.
And when the starter starts working, it drops to 10.2 V. Very high current consumption at the moment the starter rotates. But now the engine starts, and the speed stabilizes, the voltage increases - the car’s generator comes into action. With a working generator and voltage regulator, the readings multimeter should be within 13.8 - 14.2 V.
Our measurements show that the new battery purchased corresponds to the declared electrical parameters. Check completed.
