There are two ways that users usually use to check battery capacity.
Both are to fully charge the battery first and then drain it to the cutoff voltage.
According to the LiFePO4 battery specifications listed, the standard charge and discharge current is 0.5C, which means that a 100Ah battery can be tested with a load current of 50Ah.
In fact, the capacity of LiFePO4 batteries is not affected by the discharge current, so it is not necessary to strictly follow the 0.5C conditions for testing.
Especially for a 280Ah battery cell like LF280N, it is difficult to build a 140A load environment for testing.
1, Testing with practical applications
The way to test with real world applications is to use your existing equipment as a load for battery capacity testing.
The advantage is that you can test quickly and at no cost, but the disadvantage is that the error may be slightly larger.
However, this way is sufficient to make a rough estimate of the actual battery capacity.
The testing steps:
- Fully charge the battery.
- Connected to the load device.
- Record the time from the start of the equipment working to the cutoff of battery power.
- Calculate the battery capacity based on the formula – the capacity = equipment operating current * operating time.
For example, it is known that the equipment operating current is 20A, a total of 6 hours of work, then the battery capacity is 20A * 6h = 120Ah.
It should be noted that the current here refers to the current pulled from the battery side when the device is working, not the rated current of the device itself.
Because this test may involve the inverter conversion efficiency and the device’s own error, the final result may not be very close to the real capacity of the battery. But it will not be too far off.
2, Using the meter measurement
Dummy load capacity tester can be more accurate measurement of battery capacity.
- Fully charge battery;
- Connected to the dummy load capacity tester and set the load parameters;
- Read the measurement results when the battery is cutoff;
This process does not require any calculation. Dummy load capacity tester will record the battery capacity.
The final battery capacity result you get should be comparable to the rated capacity of the battery.
Of course, there may still be factors influenced by temperature/linear resistance/the measuring device itself, but such factors have not too much effect on the final result.
You can also eliminate some of these errors by doing a few more cycles.
Generally, any error within 5% can be considered to be caused by environmental factors.
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