How to battery basics

How to choose a pack and treat it right

Whether you are a rank beginner or an RC pilot with glow fuel experience who has decided to try electric-powered flight, you need to know some facts about batteries and charging before you head out for that first "clean and quiet" flight. This article explains the basics of the batteries you will come into contact with and the techniques necessary to charge and maintain them.

BATTERIES

To get the maximum enjoyment out of electric-powered flight, you will need to use batteries intended for fast charging in the field. Ideally, you should be able to get 8- to 10-minute flights on a charge and be able to "fast" recharge the batteries in approximately 20 minutes. Using multiple battery packs, it is possible to fly almost continually; one pack can be in the plane while another is on the charger.

Batteries suitable for fast charging are available from companies such as Batteries America (also known as E.H. Yost & Co.), B&T R/C Products, TNR and others. The capacity of these cells is generally stated in milliamp hours (mAh); a battery rated at 1200mAh is capable of supplying 1200mA (or 1.2 amps) of current for one hour, after which it is fully depleted.

The most common battery type is the nickel-cadmium (Ni-Cd) pack. These are available with either fast-charge or overnight-charge-type cells. The fast-charge packs tend to power larger, electric-powered aircraft, while the overnight-charge cells are more commonly used in micro and parking-lot models, as well as in radio systems (receivers and transmitters). Capacities can range from as little as 50mAh all the way up to 5000mAh (5 amp hours). The specific capacity of a cell or a pack is usually stamped right on the product. If you can't find a marking, ask the manufacturer or distributor because you need to know the capacity to determine the proper charge current. Of course, the higher the capacity of the battery, the more it will weigh. Everything in electric-powered flight is a careful balance of motor power (wattage), battery capacity, battery voltage (determined by the number of cells in the pack) and weight. Get the correct balance, and you will obtain the longest flights with maneuverability that can rival glowpowered models.

A newer type of battery now becoming very popular is the nickel-metal-hydride (NiMH) pack. NiMH cells are somewhat lighter than Ni-Cd cells of comparable capacity but supply significantly less current than an equivalent Ni-Cd. Also, the fast-charge current has to be limited with NiMH cells; otherwise, battery life will be substantially shortened. But by respecting their limitations, you can end up with more capacity in a lighter battery.

An even newer type of battery is the lithium-metal variety, which has found favor in the new, upcoming world of indoor micro RC flight. Lithium-metal cells offer weight and capacity advantages over more conventional batteries, and they produce more than twice the voltage per cell, so fewer cells can be used. But at present, the size and capacity choices with lithium-metal cells are limited, and the cells are expensive. Also, they can only be charged with chargers designed specifically for that purpose.

This article is an overview of battery and charging techniques and is intended to get electric-flight newcomers up to speed. If you have any questions or comments on this or related topics, please feel free to write to me c/o Model Airplane News, 100 E. Ridge, Ridgefield, CT 06877-4606 USA.

Copyright Air Age Publishing Apr 2001
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