NiMH Battery Testing Aux Battery - MSXV
- Darton Li
- Jenna Kong
Nickel metal hydride batteries have to be tested for internal resistance in order to group them into groups for each battery pack. This is because internal resistance is a good measure of how closely batteries match together, and how well they will work together.
For a proper NiMH battery pack, it is necessary to group them both by capacity and internal resistance.
Thus far, a procedure for internal resistance has been determined.
As there is not enough time for very thorough characterizations, the internal resistance will be entirely calculated via a high-drain ohmic resistance test. Typically NiMH packs would be grouped by AC impedance across various frequencies, as well as DC resistance at a lower drain rate and a higher drain rate, but time is short and the aux pack only requires undergoing a few cycles, which decreases the importance of a highly-matched pack. For more information on measuring internal resistance, see BU-902: How to Measure Internal Resistance - Battery University.
Internal Resistance Tests
Required Materials:
Solder station
Contactor
Battery Holder
Shunt Resistor
Multimeters (2 pcs)
Banana Cables (Handful)
Setup:
Place all components on a level surface
Plug cable marked SCOPE+ and SCOPE- connected to the shunt resistor into the same multimeter. Set to voltage measurement
Plug banana cables from FORCE+ and FORCE- or SENSE+ and SENSE- into another multimeter. Set to voltage measurement
Directly wire COIL TERMINALS to solder station power terminals
Done!
Procedure:
Label a cell with its index. This is corresponding to the address of testing, and should be on the spreadsheet (Link here later). Place it in the cell holder, carefully.
Flip the switch on the solder station, which shorts the battery across the SHUNT RESISTOR.
Wait 3 seconds, and take a picture of the voltage measured on the multimeter reading the voltage across the shunt resistor. Record this voltage in the spreadsheet (picture here)
Turn off the switch on the solder station
After 3 seconds, record the voltage read on the multimeter reading the SENSE or FORCE ports in the spreadsheet
Carefully remove the cell.
Repeat until all cells are complete.
Spreadsheet in question:
MAHA Cell Characterization - Google Sheets
Capacity Tests
Required Materials:
One source-measurement unit (SMU)
Battery holder
Instructions:
On battery holder, plug FORCE and SENSE into corresponding pins on SMU
Place cell into cell holder
Drain a fully-charged cell using a set discharge current on the SMU. Note how long it takes to fully discharge (1.0V).
Repeat for all cells.
This test can be automated through the use of a python script using the PyVisa library over a connection to the GPIB connector of the SMU.