jtr1962
Flashaholic
I purchased eight of these cells to power a pair of bike lights and thought I would share the results of my testing. I ran capacity tests on all eight cells at both 0.2C (660 mA) and 0.5C (1650 mA). I also tabulated the results of charging the same cell at both 660 mA/3.65V and 3300 mA/3.65V, plus discharging it at 0.2C, 0.5C, 1.0C, and 2.0C.
First, the capacity test results of all eight cells at 0.2C discharge in mAh:
1-3290
2-3273
3-3195
4-3244
5-3257
6-3279
7-3179
8-3210
Capacity test results at 0.5C discharge in mAh:
1-3220
2-3204
3-3130
4-3181
5-3208
6-3190
7-3132
8-3133
The cells are speced at 3200 mAh minimum at 0.2C discharge to 2.00V at 23°C. They all either exceed this or come very close. Note that the test area was around 19°C. This would account for some cells falling a little short. Also, there is a margin of error in my results because I only measured current to 0.1% accuracy. One interesting thing to note is the 0.5C results fall about 2% short of the 0.2C results, but if I let the cells recover to 3.00V, then discharge again to 2.00V, the capacity results are very close to the 0.2C numbers.
Here is a chart of my testing of cell number 2 at various charge/discharge currents:
The maximum continuous discharge current is 2.0C, or 6.6 amps. The cell voltage sags by roughly 0.25V compared to 0.2C discharge, but the cell still performs rather well, delivering 3146 mAh ( compared to 3276 mAh when discharged at 0.2C ). In my planned service the cells won't see anything above about 0.5C, and then likely only for short bursts. Most of the time they will be operating at 0.2C or less.
It's interesting also to compare the amount of charge and energy in and out of the cell. At 0.2C discharge the cell put out 10,416 mWh. This dropped to 9,106 mWh when discharged at 2.0C, the difference going into heating the cell (it reached about 45°C). Here is a chart of the both the current and energy efficiencies at different charge/discharge rates:
Note first of all that the current efficiencies are pretty close to unity. This makes sense. Generally mAh out equals mAh in. The energy efficiencies ( energy out divided by energy in ) get worse if either charge current or discharge current is increased. This makes sense because the cells have a non-zero value of internal resistance. Still, the results are interesting. Even worst case ( 3300 mA charge, 6600 mA discharge ) you still recover over 78% of the energy you put into the cell. At 0.2C charge/discharge you recover over 93%. I assume these numbers would approach unity as the charge/discharge currents approached zero.
Overall, I'm pretty impressed with these cells given their low cost. They meet their specs and hold up OK under high discharge currents (although not as well as the A123 Systems cells).
First, the capacity test results of all eight cells at 0.2C discharge in mAh:
1-3290
2-3273
3-3195
4-3244
5-3257
6-3279
7-3179
8-3210
Capacity test results at 0.5C discharge in mAh:
1-3220
2-3204
3-3130
4-3181
5-3208
6-3190
7-3132
8-3133
The cells are speced at 3200 mAh minimum at 0.2C discharge to 2.00V at 23°C. They all either exceed this or come very close. Note that the test area was around 19°C. This would account for some cells falling a little short. Also, there is a margin of error in my results because I only measured current to 0.1% accuracy. One interesting thing to note is the 0.5C results fall about 2% short of the 0.2C results, but if I let the cells recover to 3.00V, then discharge again to 2.00V, the capacity results are very close to the 0.2C numbers.
Here is a chart of my testing of cell number 2 at various charge/discharge currents:
The maximum continuous discharge current is 2.0C, or 6.6 amps. The cell voltage sags by roughly 0.25V compared to 0.2C discharge, but the cell still performs rather well, delivering 3146 mAh ( compared to 3276 mAh when discharged at 0.2C ). In my planned service the cells won't see anything above about 0.5C, and then likely only for short bursts. Most of the time they will be operating at 0.2C or less.
It's interesting also to compare the amount of charge and energy in and out of the cell. At 0.2C discharge the cell put out 10,416 mWh. This dropped to 9,106 mWh when discharged at 2.0C, the difference going into heating the cell (it reached about 45°C). Here is a chart of the both the current and energy efficiencies at different charge/discharge rates:
Note first of all that the current efficiencies are pretty close to unity. This makes sense. Generally mAh out equals mAh in. The energy efficiencies ( energy out divided by energy in ) get worse if either charge current or discharge current is increased. This makes sense because the cells have a non-zero value of internal resistance. Still, the results are interesting. Even worst case ( 3300 mA charge, 6600 mA discharge ) you still recover over 78% of the energy you put into the cell. At 0.2C charge/discharge you recover over 93%. I assume these numbers would approach unity as the charge/discharge currents approached zero.
Overall, I'm pretty impressed with these cells given their low cost. They meet their specs and hold up OK under high discharge currents (although not as well as the A123 Systems cells).
