The capacity of a battery or accumulator is called the amount of electricity in them (charge Q). Typically, capacitance is measured in the following units: ampere-hour or milliampere-hour. So, a battery with a capacity of 1000 milliamperes-hour can provide a current of 1000 milliamperes for an hour or a current of 100 milliamps for 10 hours. Taking into account the voltage U, the energy stored in the battery can be estimated: E = Q * U.
It is necessary
Battery capacity tester
Instructions
Step 1
Understand the principle of determining the capacity of the battery. First, charge the battery, then discharge it with a current I, and then measure the time T during which it is discharged. The product of current and time will be the capacity of the battery; calculate it using the formula Q = I * T. In the same way, you can measure the capacity of a battery, but unlike it, the battery can be recharged after a full discharge.
Step 2
To measure the battery capacity, use a circuit that discharges the battery through a resistor R to a voltage of about 1 V. Measure the discharge current according to the formula I = U / R. To measure the discharge time, use a clock that can operate on a voltage of 1.5-2.5 V To protect the battery from full discharge, use a solid-state relay, for example, PVN012, which will disconnect the battery when the voltage drops to the minimum allowable (in our case, to 1 V).
Step 3
Fully discharge the battery and connect it to the circuit. Set the clock to zero and turn on the circuit. In this case, the relay will close the contacts, the battery will start to discharge through the resistor, and the voltage will be applied to the clock. The voltage across the resistor and battery will gradually decrease, and when it reaches 1 V, the relay will open the contacts. When the discharge stops, the clock will stop.
Step 4
Please note that the capacity of a newly charged battery is higher, since over time, part of the charge is lost during self-discharge. In order to find out the amount of self-discharge, measure the capacity immediately after charging, and then take the measurement after a week (month). The permissible self-discharge of NiMh batteries is about 10% per week.
Step 5
Improve the wiring diagram to reduce the resistance of the battery contacts. In some battery holders, losses can be caused by a steel spring, which is recommended to be shunted using a copper wire.
