Kite Aerial Photography Electronic Resources--Batteries Page 1

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Battery Fundamentals

March 26, 2002
by David Hunt
INTRODUCTION Batteries are a much neglected part of KAP cradle design. Little thought is given to batteries other than making sure they are charged prior to use. There are significant options to powering the electronics on board a KAP cradle. On this first page we will discuss different types of batteries and some of the terms and characteristics of batteries. After studying this information you will be better equipped to make an informed decision about your KAP cradle's power system. The second page is titled "Special Battery Strategies", and looks at ways to save weight with your battery system. BATTERY TYPES The are 5 battery types that you will run across. Lead Acid Batteries - this is the type of battery found in a car. Even small lead-acid batteries are too heavy for use on a KAP cradle, but could easily be used to power ground equipment. Small lead acid batteries are the size of a P&S camera but they can have a substantially greater ampere hour rating than the other 4 types. Primary Cell Batteries - included in this group are alkaline, and lithium (not Lithium-Ion) batteries. The AAA through D size cells that you find at most stores are in this category. They are not rechargeable, and few KAPers use these batteries because the long term costs are high. This group as a whole will have the lowest ampere hour rating per unit of all the other types. Nickel Cadmium Batteries (NiCd) - NiCd batteries are rechargeable and have been used in portable electronic equipment for years. This is the type of battery pack that the major radio control manufacturers supply with their systems, such as the 4.8 volt Futaba battery pack at the top of the page. Nickel Metal Hydroxide (NiMH) - A relative newcomer to the rechargeable battery scene. NiMH batteries offer more power per unit weight than NiCd batteries. NiMH batteries are also environmentally friendly whereas NiCd's require proper disposal at the end of their life. Lithium-Ion (Li-ion) - Li-ion batteries have become standard in many cell phones and digital cameras. They offer an even greater weight savings over the NiMH batteries. Li-ion batteries require special charging techniques that are not compatible with NiCd and NiMH batteries. ELECTRICAL POWER NEEDS To chose a battery system to power any of your KAP equipment you will need to know the amount of current used by each piece of equipment. Each device will have a current rating in amperes. Amperes is often shortened to "amps" or just a capital "A". When you see "mA" this stands for milliamperes, or thousandths of an ampere. Below is a short list of power requirements for some typical KAP equipment. Futaba RC Transmitter 180 mA Futaba RC Receiver 10 mA Futaba 3003 Servo (idle) 8 mA 2.4 GHz TX from Xcam2 ~50mA	AMPERE-HOURS Ampere-hour is a measure of the amount of energy stored in a battery. Rechargeable batteries will have an ampere-hour rating listed somewhere on the battery, non-rechargeable batteries may not have a Ah rating listed on the battery. The acronym for ampere-hours is Ah and for milliampere-hours the acronym is mAh. The Futaba NiCd battery pack label is pictured below. NiCd Close-Up The label indicates that this battery is rated at 600 mAh. Theoretically dividing the ampere-hour rating by the number of amperes being used will tell you how long the battery will last. This would mean that this battery would supply 600 milliamps for a period of one hour. 300 milliamps for a period of two hours 60 milliamps for 10 hours. In reality the amp-hour capacity will be decreased by higher current demands, and by temperatures higher or lower than room temperature. I'm not sure if this is a good rule of thumb, but do not expect your battery to give you more than half of the times calculated above. ENERGY DENSITY Energy density loosely defined is the amp-hour capacity divided by the weight. Weight being of great importance when designing a KAP cradle, this subject deserves some discussion. If you have two cells of equal amp-hour capacity, the cell with the greatest energy density will weigh less. Rating the 4 rechargeable battery types from the lowest energy density to the greatest energy density; LOWEST Lead Acid Batteries Nickel Cadmium Batteries Nickel Metal Hydroxide Batteries Lithium Ion Batteries GREATEST Although not entirely related to the energy density, the cost of these different batteries increases with the energy density. Lithium Ion batteries have yet to see much use in the KAP community. I'm not sure if they are cost effective compared to NiCds and NiMHs. Even the chargers for Li-ion batteries seem to be more expensive. CONCLUSION There is much more that can be said about properly charging, discharging, and storing batteries. Below is a list of web sites with more battery information. The R/C Battery Clinic Editors Choice! PowerStream Technical Resources Thomas Distributing FAQ Thomas Distributing NiMH info [Ed- Use the menu box at the top of the page to the other KAPER pages about batteries]