Date: 20th April 2005 Battery Type: Thunder Power Pro-Lite Li-Po 4 x series Lithium-Polymer Battery Pack Weight: 165g Dimensions: 65mm x 49mm x 26mm Manufacturers Rating: 14.4V 2000mAh, max discharge current 10-12C* Note: All tests are carried out in a controlled 24C ambient for consistency. Author: Mark Hopkins *Not confirmed but believed to be correct at time of test Mechanical The battery is in a 4 x series Li-Po configuration, with the cells stacked horizontally on top of each other, and covered with heatshrink. The two out-put wires (+ve & -ve) appear more ‘Heavy-Duty’ than the output wires on previous packs I have reviewed, and are extremely good for micro heli application. As I have seen inside a thunder Power battery (se the Thunder Power 1300mAh report) I did not feel the need to open this battery, as I had no reason to believe that this battery would be any different. So, to recap, the cells were professionally connected to each other by spot or US (Ultra Sonic) welder. As mentioned in previous reports of other batteries, there was no protection circuit fitted to the pack to protect from over voltage, under voltage, over current, over/under temperature, cell imbalance, etc. All four cells are stacked with no air gap for the middle cells, these cells will therefore find it more difficult to dissipate heat, potentially leading to the middle cells failing early if used a extremely high currents. Electrical The voltage of each cell was measured before commencing charge and the pack was found to be well in balance. The pack was then charged to 16.8V (4.2V per cell) with a current limit of 1000mA, in a 24C ambient, and with a termination current of 50mA at 16.8V. At end of charge the cell pack was still well balanced. The pack was discharged at C rate (2000mA) with a 12.0V cut-off voltage. The capacity at this rate was 1.96Ah, 28Wh, the cell pack reached a maximum temperature of 35.7C. The battery was then charged as before then discharged at 10A and 20A respectively, the following results were recorded: At 10A the capacity was 1.93Ah, 27Wh, the cell pack reached a maximum temperature of 64.9C. At 20A the capacity was 1.88Ah, 25Wh, the cell pack reached a staggering temperature of 72.5C. At the end of the discharge tests the cells exhibited the following voltages after a 30 minute rest: Cell 1 - 3.57V Cell 2 - 3.57V Cell 3 - 3.58V Cell 4 - 3.57V Still extremely well balanced. Conclusion As usual I have to mention the lack of protection to be a concern, although this seems to be standard in the model market, and the cells in the middle of the pack could fail early if used at very high current levels due to uneven heating. Although the capacity was just below the 2000mAh rating at C rate, the performance did not drop off very much when higher current levels were demanded. The discharge graph at 20A shows the cells to be very strong. Previously, cells tested at 20A show a dip early on, and then the voltage recovers as the discharge continues. This is an indication that the cells maximum rating is being exceeded. The Thunder Power battery pack showed virtually no sign of this ‘droop’ with the voltage holding up well at 20A, although the temperature did get a little excessive at this rate. The fact that this pack is a 4 series will give a higher head voltage at the motor. This means that the current required will be lower to achieve the same watts when flying, and so a continuous 20A load from start to finish will probably not actually be reached in a micro heli. This means that the pack should run cooler than than the above figures in actual use. Mark Hopkins (Research & Development Engineer/Designer and ISO 9001:2000 Auditor for PAG Advanced Battery Systems Ltd)