| Electric model airplanes have been around for roughly | | | | has a capacity of 2.3 Ah and weighs 70 grams (2.47 |
| three decades. A huge problem in the early days was | | | | oz). A newer, smaller size can hold 1.1 Ah and weighs |
| battery energy density. In other words, they simply | | | | 40 grams (1.41 oz). |
| weighed too much for the amount of juice you could | | | | The primary source for A123 M1 cells has been |
| get out of them. This situation has improved | | | | DeWalt 36-volt portable power-tool battery packs. |
| dramatically in recent years with the advent of Li-Poly | | | | Each pack contains 10cells. I purchased two of these |
| cells, but a battery pack for a larger model can easily | | | | for $100 each through Ebay. The prices appear to |
| cost hundreds of dollars. The advent of electric cars, | | | | have gone up recently to the $120-$130 range. Single |
| such as the Toyota Prius has spurred an enormous | | | | cells can also be purchased online for $15 from a |
| amount of research into new battery technologies. In | | | | growing variety of vendors. You can find two of the |
| this article, I will describe an alternative to Li-Poly | | | | smaller cells in a Black & Decker VPX battery |
| batteries that offers intriguing possibilities. | | | | pack which sells for about $15. The smaller cells can |
| A123 Systems produces Lithium-Ion Nanophosphate | | | | also be had for $12.50 each. |
| cells. These cells have a nominal voltage of 3.3 volts | | | | There are many Li-Poly chargers that support or can |
| and can withstand continuous discharge rates of 30C. | | | | be modified to support the charging of these A123 |
| They can be safely discharged down to 2.0 volts. The | | | | cells. Because of the sharp voltage drop-off when |
| voltage remains fairly constant through the discharge | | | | discharged, you are probably better off using a timer |
| cycle, but they do have a sharp drop-off at the end. | | | | when you fly. Otherwise you need your ESC to shut |
| Expect 300 cycles before you notice any reduction in | | | | off the motor when 2.0 volts per cell is reached. |
| capacity while at 1,000 cycles you'll have 75% of the | | | | Bottom line? These cells give you 70% the energy |
| original capacity. They are very safe. Overcharging or | | | | density of Li-Polys for about 45% of the price. For |
| over discharging will not cause an explosion and will | | | | many of us, that is a good trade-off. They are |
| have little effect on the life of the battery. Balancing | | | | extremely safe and can be charged in 15 minutes. If |
| the cells when they are charged is still a good idea, but | | | | you end up buying half as many battery packs |
| not absolutely required. They can be charged | | | | because of the shorter charge time, then they |
| immediately after use in 15 minutes. | | | | become a much better value. |
| The cells are available in two sizes. The original M1 cell | | | | |