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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 Expansion Channel mode, use the list in the right panel to
display data from a selected channel.
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 without
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 Dual PowerLab 8x2 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 charged from
below
75% of capacity. It takes less than 3 minutes to calculate internal resistance.
Internal resistance can only be calculated during charging, and only when the
pack is connected using both the balance wires and discharge wires.
Summary of Contents for Dual PowerLab 8x2
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