For your rc electric airplane? How expensive is a radio control lithium battery? A nickel cadmium rc battery? A nickel metal hydride? With so many choices, how do you select one for your plane?
Nickel Cadmium or NiCad batteries are now the old stand-bys. They are commonly supplied with new radio packages from the leading manufacturers such as HiTek, Futaba, JR and others. They use basic chargers and electronic speed controls (electric throttles), are physically fairly robust and can be recharged many 100’s even 1000’s of times with no special precautions. Furthermore, NiCad’s are affordable and provide good rapid discharge when used to power electric motors. However, they are the heaviest of the three and this is not desirable for electric rc airplanes.
Nickel Metal Hydride or NiMH batteries appeared on the rc market just a few years ago and offered the major advantage of being about 50% lighter than equivalent NiCad’s. But they also required a new breed of charger which could provide a constant voltage to avoid overheating and destroying the cells in the battery packs. Because the weight advantage in electric flight is so significant, many modelers chose these batteries which also offered the benefit of a longer discharge time for more and longer flights.
The radio control lithium battery became all the rage during the past 2-3 years with the advent of lithium polymer batteries in which a dry polymer was used as the electrolyte (like the acid in the lead acid battery). This made the radio control lithium battery physically more stable, easier to manufacture, lighter and relatively safer. (Although there are definite safety precautions to be observed in the charging and disposal of these batteries). The advantages to the electric rc airplane are 1/3 the weight of NiCads, faster release of the stored electrical energy (in short bursts) and reduced size.
Charging of the radio control lithium battery is by a special LiPo batteries-only charger, and the battery MUST be removed promptly when charging completes to reduce the danger of over-charging. Overcharging can result in possible explosion and fire from the cells.
Many battery manufactures are now including overcharge protection built into the cells. Also needed are special LiPo ESC’s which monitor in-flight cell voltages to stay above the safe minimum of 1.1 volts per cell.
Pricing: as a rough gauge, a 7 cell 600 Ma NiCad @$20 would be replaced by a 7 cell 1000 Ma NiMH @ $25 or by an 11.1 volt 830 amp LiPo @ $40.
Flying times might be 5-7 minutes for the NiCad, 8-11 minutes for the NiMH and 15-18 minutes(!) for the radio control lithium battery. So once again, we pay for performance, but these dramatically improved flight times have been a major reason for the rocketing popular,interest in electric flight during the past two-three years.