Samsung SDI INR21700-40T
Series: Samsung SDI Battery cells for drone packs
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The Samsung INR21700-40T is a high-drain cell in the 21700 format from Samsung SDI, a South Korean battery maker. Its INR21700 cells 40T, 50S and 50E are common in lithium-ion packs for FPV and drones. The 40T is intended for small FPV drones and comes in the variants 40T3 and 40T5. The format 21700 stands for 21 mm diameter and 70 mm length.
The cell stores 4,000 mAh at 3.6 V nominal voltage, which is 14.4 Wh per cell (nominal voltage times capacity). The continuous current is 35 A, which is 8.75C, calculated from current and capacity; at that current the cell is empty in under seven minutes. The weight varies with the source: 68.7 g at one dealer, 67 g for the 40T5 variant, at most 70 g at a third. A pack therefore cannot be planned to the gram in advance.
Six cells in series (6S1P) come to 86.4 Wh and so stay below the IATA limit of 100 Wh for spare batteries in passenger flights. Lithium cells must meet the tests of UN 38.3 for transport and are packed protected against short circuit. In addition, IEC 62133 covers the safety of lithium cells in portable devices; whether a cell is tested to it is stated in the manufacturer's data sheet. Joining cells into a pack belongs in a specialist workshop with test and protection equipment.
When choosing, check whether the pack current stays well below 35 A, because in a series string every cell carries the full current. High-drain cells such as the 40T are often counterfeited, and the variants differ in weight; in a pack of several cells all should come from the same variant and batch. Cold increases the voltage sag, and heat speeds up ageing.
Technical data
Other data
| C-rate | 8.75correct |
|---|---|
| Capacity (mAh) | 4,000correct |
| Cell chemistry | Li-Ioncorrect |
| Cell count (S) | 1Scorrect |
| Continuous current (A) | 35correct |
| Form factor | 21,700correct |
| Nominal voltage (V) | 3.6correct |
| Weight (g) | 68.7correct |
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