Burgerman wrote:Amazon doesent sell impedance testing tools. Its NOT a volt meter.
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.
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.
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:
(Note to expresso, the hobby packs we use are not 1C or 2C but anything up to 150C! -- burgerman)
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.
(Note to expreso, the hobby packs talked about below may be 3Ah not 200... And LIPO - Burgerman)
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 8 as a tool, measuring and record 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.
could be the cell i was charging - was a Low C rate and i charged it at 25A - too much for that cell but the IR was 78 - so way out there
cell looked brand new to me - QC sticker - everything -
My el cheapo multimeter and old, beatup, oxidized leads give me ca. 1 to 2 ohm indicated. 0.1 ohm = 10 mOhm is probably John's Fluke.
Low ohms (LoΩ): allows you to measure lower resistance in circuits more accurately through compensating for the natural resistance in the probe leads, as well as through high resolution. The 289 has its own low ohms (50Ω) range position.
LROBBINS wrote:My
0.1 ohm = 10 mOhm is probably John's Fluke. .
LROBBINS wrote:M6 studs already installed - I don't know if welded or otherwise. I don't recall the height, but I'll try to remember to measure one tomorrow.
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