REVLC06S40A-SPA-MC Revolectrix PowerLab 6 Manual

Internal Resistance tab

The Int. Res. tab displays cell internal resistance when charging LiPo and A123

balanced packs. Internal resistance is not calculated or displayed during discharge

cycles.

If you are charging using multiple PowerLabs set for Expansion Channel mode, use the

list in the right panel to display data from a selected unit.

Viewing individual internal cell resistance enables you to more accurately evaluate pack

quality and condition. If all cells show a low internal resistance, that’s a good indicator

that the pack can be charged and discharged at a higher C rate. Here are two examples:

 A pack rated at 5C and 40–50C discharge may have an internal cell resistance of 2

milliohms. This low resistance allows larger currents into and out of the pack with-out

generating excessive heat. 

 A pack rated at 2C charge and 20–30C discharge may have 17 to 20 milliohms

internal cell resistance. The higher resistance prevents the pack from charging or

discharging as quickly, and the larger resistance will generate more heat during those

operations.

A cell poorly matched to the other cells in a pack will show a substantially different

internal resistance. Also, a cell with high internal resistance compared to other cells may

indicate the cell is weakening, which can degrade overall pack performance.

Be aware that individual cell resistance will vary during charge. This is normal and

results from the different voltages and currents applied to the pack during charging.

Use the PowerLab 6 as a tool, measuring and recording the internal resistance of your

packs over time. Look for trends that would indicate the IR of a cell or a pack is

increasing over time. This is a good indication that the pack is aging or has internal

damage and should be replaced eventually.

Note: Internal resistance can only be measured on packs with a state of

charge below 75% of capacity. It takes less than 3 minutes to calculate

internal resistance. Internal resistance can only be calculated during charging.