Testing a battery module

Testing a battery module is obviously an extension of testing a battery cell. Again, we can perform the following tests:

  1. Determining the impedance of the battery module
  2. Determining module capacity
  3. The number of charge/discharge cycles

We now know the effect of charging with too high a voltage and discharging a Li-ion battery too deeply when looking at a battery cell. The effects on a battery module are similar to those of a battery cell and so we will not cover them here.

An isolation test on a battery module can be done but before integrating the Battery Management System (BMS).

THE BATTERY MODULE IMPEDANCE TEST

This test is actually similar to the impedance test at the battery cell. There is also the possibility of a DC test and an AC test. With the DC test, you now only have to deal with a slightly higher battery voltage, so you need a slightly higher load for good test results.

Such a test also indicates right away whether the connections (welds) of the battery cells succeeded well.

For a complete overview of our (regenerative) DC loads, please refer to the DC loads overview.

With dynamic loads, the internal capacitance is also important. This measurement is performed at a specific frequency (usually 1kHz) or is performed over a wide range of frequencies to further determine the dynamic behaviour of the battery. These are always four-wire measurements with generally very low impedance values. For possible solutions see, for example, the Itech IT-5101H with ranges up to 1000V.

DETERMINING THE CAPACITY OF THE MODULE

This test is also basically the same as testing the capacity of a battery cell. Of course, here we are dealing with higher DC voltages and a higher capacity but the principle of the measurement remains the same. It is important to draw up a clear script containing the conditions under which the capacity of the battery is determined.

  1. What is the maximum charging voltage?
  2. To what voltage can the battery be discharged?
  3. What is the discharge current or discharge current cycles?
  4. At what temperature does it discharge and charge?
  5. With what charging current is the battery recharged as well?

And are these also values in line with your application of this battery? A battery used at sea in a buoy has a very different ambient temperature and charge/discharge cycle as the battery in, say, an electric car. Depending on the voltage and capacity of the battery module, (regenerative) bi-directional DC power supplies are often used for testing in this case.

For small modules, in TTMS’ product portfolio we have two quadrant DC power supplies in the voltage range of 0-20V and 0-60V with outputs from 60W to 150W and above. The regenerative bi-directional DC power supplies start at 0-60V, 200W to 18kW but also 0-2250V at 18kW. And especially at the high power levels, it is interesting to work with regenerative units. This saves you double on energy costs and sometimes even more. Double because you not only return the energy from the load to the grid (around 80% efficiency) but also because you save a large air-conditioning unit and the associated energy bill. A third potential saving lies in the fact that because you are pumping the energy around, you do not need an extra heavy connection to the power grid with all the associated costs. For the relatively low voltage/high current modules (6V, 12V, 24V), Magna Power solutions in the TS series can be used. In this line, we have DC power supplies from 10V up to 8000A and 25V up to as much as 4000A. These in turn can be combined with H&H’s SCL DC loads in the 12V or 40V version up to a maximum of 6000A.

THE NUMBER OF CHARGE/DISCHARGE CYCLES

Of course, we would also like to know the battery module life. And the same conditions (and more) as for the capacity test also apply here.

  1. What is the maximum charging voltage?
  2. To what voltage is the battery discharged?
  3. What is the discharge current or discharge current cycles?
  4. At what temperature does it discharge and charge?
  5. With what charging current is the battery recharged as well?
  6. At what temperature is the battery module charged?
  7. Is the battery also charged dynamically?
  8. From what capacity does the battery recharge?
  9. From what capacity does the battery discharge?

In these tests, we can of course again use the same equipment as in the capacity test but generally this involves long-term testing in a 24/7 test cycle of sometimes months. And then also usually with several modules at the same time and possibly also spread over several climate chambers.

Regenerative bi-directional DC power supplies are clearly preferred here given the length of the test period. TTMS also has several options here. For example, test systems with several ‘separate’ units and comprehensive test software from the manufacturer Itech. Here, several bi-directional power supplies can also be combined into one system.

Depending on powers and voltages, we go from 8 to 56 channels, 0-60V, 0-600W to 2.5kW modules with voltages of 0-100V and 0-500V in configurations from 4 to 20 channels and more. Configurations are possible up to 20kW per channel at a maximum voltage of 500V in this series. Test solutions with higher powers, currents and voltages are also possible but these are generally single-channel battery pack test solutions.

For this, see also testing a battery pack.

We also have a page highlighting battery test software/systems.


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