upgraded the rig, and ran some more measurements:
summary: some improvements, but 0.5A discharge is still 3066, lower than any other NCR1850B test I’ve seen.
Rig update:
- made new charging cables with 12AWG wire, silicone insulated from hobbyking, solered and screw-pressed into connectors. Can’t get much better connection than that.
- Press-fitted the stripped wires directly to battery terminals using a vice
Measurements:
- measured for voltage drop on charging terminals - at 5A discharge I get 0.006V votage drop in the 12AWG terminals
- during 5A discharge: measured input voltage to compare what multimeter sees against what the charger detects: at 5A discharge multimeter sees the battery with 0.3V higher voltage than the charger sees it. This equates to the charger’s current meter having it’s own internal resistance of 60mOhm. This could partially account for much lower capacicity at higher current discharges because of premature termination, but the 0.5A discharge capacity is still much less than it should be.
- Used calibrated fluke multimeter to check if charging current and termination voltage of the charger are correct, charger reports cca 1.5% lesser current than multimeter, and cca 0.03V higher voltage than multimeter. Don’t find this significant.
- mystery: charged and discharged capacities mismatch, measured charged always lower than measured discharged.
Notes:
- With new connection wires can charge and discharge at much higher currents
- Discharged capacity still much lower than it should be at all currents
This is how I cycled the battery, sequentially:
Step 1: Discharge
Current: 3.4A (1C)
Discharged capacity: 2260mAh
Step 2: Charge
Current: 1A
Charged capacity: 1893mAh (I can’t think of a technical reason why the charged capacity is lower than the just previously discharged???)
Step 3: Discharge
Current: 2A
Discharged capacity: 2774 mAh (Again, higher than the just charged capacity)
Step 4: Charge
current: 1A
charged capacity: 2473mAh (lower than the previous discharge)
Step 4: Discharge
Current: 0.5A
Discharged capacity: 3066mAh (higher than previous charge)
Rig pictures: