By Evan Chapkis Evan_Chapkis@RCAccessory.com
I ended last months article saying that we'll discuss
capcity of a lithium battery. Capacity is just like your fuel tank. If you have a 20 oz tank, you'll get x number of minutes
of flight. This is true for an electric powered aircraft as well but there are some things that come into play with
electrics that are not relevant in a glow or gas aircraft.
With a glow or gas powered aircraft, you have the same motor
output from the beginning of the flight to the end. With an electric, as the voltage drops, so does your totals watts output.
In a glow or a gas powered aircraft, if your tank and plkumbing are correctly installed, you can fly the full 20 oz tank if
you like with only having to worry about a dead stick landing.
A lithium battery should only be drained no more than
80% of the capacity of the battery. So the 2200 mah 3S 30C battery you have does not have 2200 mah of usable capacity, it
has 1760 mah of usable capacity. If you draw more than 80% of the capacity out of the battery, it will be damaged. Damage
in a lithium battery is cumlative, meaning that everytime you over discharge, over amp, or even over charge a lithium battery,
some damage is done and it cannot be recovered. Damage will show itself with the infamous "puff" or swell, become
severly out of balance where the balance charger cannot balance the pack, shorter flight times and increased heat. Unlike
nicads and nimh cells, lithium does not benefit from cycling.
One of the questions I get asked often, "What size
battery (capacity) do I need?" The reason this is not necessarily an easy answer is due to size and weight of the battery.
If you have a small aicraft that the kit calls for a 2200 mah 3S battery, yes a 5000 mah 3S will work as far as powering the
motor, the but the physical size and weight will be in most cases too much.
Many foam aicraft, especially the EDF jets
have small battery compartments and plane was designed for a specific sized battery. If you can fit a larger battery in the
compartment, make sure you check the CG.
Next month we'll discuss the tools of the electric flyer. See you at the field.
