The testing of a battery pack

The testing of a battery pack

The testing of a battery pack is an extension of the testing of a battery module.
Here we can also perform the following tests:

– Determining the impedance of the complete battery pack
– Determining the capacity of the battery pack
– The number of charge/discharge cycles

Compared to the testing of the battery modules, we are dealing here with higher capacities (kWh), higher currents and more and more also higher voltages. And this in itself also presents new challenges. At the moment we see battery packs for buses and trucks with voltages up to about 800V. However, developments are already going up to 1000 and 1200V battery packs.
The greatest challenge, however, lies in the charging currents. Using a pantograph, we can charge with quite high currents. But the electric truck does not yet have a pantograph. The challenge lies in cooled charging connectors in order to have a manageable cable that can handle high charging currents. And when we hear what the future plans are, especially for long-distance trucks, we will see charging currents of 2000A and more at a maximum charging voltage of 1500V. There are still some challenges to be met.

DETERMINING THE BATTERY IMPEDANCE

The internal resistance of a battery pack can be determined quite simply by means of a step response measurement in the load of the battery. See also the explanation of this method in the page testing a battery cell.
You need however a somewhat heavier load. There are now bi-directional DC power supplies that can handle these voltages and currents well.

DETERMINING THE CAPACITY OF THE BATTERY PACK

And here again, the same conditions apply as we mentioned when testing a battery module, only now we are working with higher capacities. Especially with these high powers, we see the advantages of using (regenerative) bi-directional DC power supplies.

For the small packs, we have two quadrant DC power supplies in the TTMS product portfolio in the voltage range from 0-80V through to 0-1500V at power ratings from 5kW to 18kW. These power supplies are fully adapted to these applications and have the possibility of an autonomous charge and discharge cycle with the customer’s desired parameters. By means of set values such as charge/discharge voltage, current and time, charging or discharging can take place. In addition, we have the stop values for charging and discharging in the form of stop voltage, stop current and stop capacity. With a single bi-directional DC power supply there is also the possibility of connecting a temperature sensor so that the temperature of the battery can also be a stop value.

For quick chargers for cars we already see capacities of 22kW or even 44kW. For trucks and buses this is already up to 600kW and more. We expect the first chargers of 900kW and 1200kW on the market soon. For boats, we have already seen a 6MW charging station.

With most bi-directional DC power supplies, we can build a test system by putting a number of units in a master/slave configuration to create configurations as high as MWs.

However, we also have solutions with bi-directional DC power supplies of 60kW (max 300kW) and a modular system with 15kW to 160kW modules that can be combined to >1.2MW installations with a maximum voltage of 1500V.

THE NUMBER OF CHARGE/DISCHARGE CYCLES OF A BATTERY PACK

If these tests are already carried out on the complete pack (usually this is limited to the battery module), then these are lengthy and costly tests. For the tests the same hardware can be used as for the capacity test and then often supplemented with extensive battery test software.

With the B2C hardware of Cinergia we can also test up to three packs with a maximum power of 53kW per pack simultaneously.

RELATED TOPICS

Battery testing

Battery testing safety.

Testing a battery cell.

The testing of a battery module.

Battery test software / systems.