Lipo Battery Information
Useful information on lipo battery use and safety
NiCad, NiMH and Lipo battery information
Electric power has changed radio control model airplane flight forever. The ability to power a range of aircraft, from small micro indoor ParkZone aircraft or the UFO flying saucer to scale models such as the Blackburn plane to much larger outdoor stunt planes, with easy to use electric motors has opened up a much wider variety of flying locations and aircraft prototypes for the RC pilot enthusiast.
The batteries carried by these model aircraft are the key to successful electric flight. Early electric RC models used Nickel Cadmium (NiCad) and Nickel Metal Hydride (NiMH) rechargeable batteries. The Lithium Polymer (lipo) battery is now the latest technology to power electric radio control model airplanes. A lipo battery offers several times the capacity and run time of the older NiCad and NiMH batteries. In addition, a lipo battery is much smaller and weighs much less than the older rechargeable batteries. Especially with the smaller micro electric RC aircraft, a small, lightweight lipo battery is essentially a requirement for success with these miniature flyers.
A lipo battery is completely different as compared to NiCad or NiMH batteries. It is vitally important that you understand these technical features of a lipo battery for best performance and safety. An individual lipo battery is made up of a single cell with a nominal voltage of 3.7 volts, vs. the more typical 1.2 volts of a NiCad or NiMH battery. A lipo battery cell can be wired in series, with two lipo battery cells in series equaling 7.4 volts, and three lipo battery cells in series equaling 11.1 volts.
A lipo battery cell can also be wired in parallel. Using two lipo battery cells wired in parallel doubles the pack capacity, allowing for longer flight times. In addition, a lipo battery wired in parallel allows each cell to see half of the total current.
By adding the number of lipo battery cells wired in series one gets the total voltage (three lipo battery cells in series would equal 11,1 volts). Two of these three lipo battery cell packs combined and wired in parallel double the capacity of the single three cell pack. In this example, use of two of these three lipo battery cells wired in series would be referred to as a 3S 2P battery (3 series, 2 parallel).
Lipo battery chemistry
A lipo battery uses a different chemistry and materials than the NiCad or NiMH batteries, and you must use a charger designed specifically for a lipo battery. There are a wide variety of chargers available for a lipo battery. It is vital that a lipo battery charger’s directions be carefully followed to avoid an improper battery charge profile. A lipo battery that is not properly charged can easily catch on fire. We never faced this unhappy situation with the NiCad or NiMH batteries, which are very tolerant of improper charging procedures. Some models, such as the ParkZone Sukhoi, have extremely safe lipo battery chargers. However, due to the unique construction and chemical makeup of a lipo battery, they can literally catch fire and explode if not properly charged.
Safety is the number one focus when you are using a lipo battery for your radio control model aircraft. The best course of action is to use a quality lipo battery from a recognized company; use a charger specifically designed for a lipo battery; and be absolutely certain that the correct number of lipo battery cells is entered (or sensed, if automatic) into the lipo battery charger. The following lipo battery “Do’s and Don’t's” shall be followed without question!
Do: Do use a charger designed exclusively for charging a lipo battery. Failure to follow this rule can easily result in a lipo battery fire or explosion.
Do: Do use a balancing charger. Each lipo battery cell has an individual technical characteristic, and over several charge/discharge cycles can acquire differences in capacity from another cell in the same lipo battery pack. Even though lipo battery cells may be matched when a cell is constructed, a balancing charger can account for cell charge changes over time.
Do: Do store your lipo battery with at least a partial charge. Unlike with NiCad or NiMH batteries, a lipo battery does not keep a “charge memory,” and you do not have to cycle them.
Do: Do attend your lipo battery when it is being charged, and charge in an open and ventilated area. Lipo battery fires can happen very quickly, and you simply have to be there to keep your house, car, or garage from being incinerated.
Do: Do use a fire safe area to charge your lipo battery. A fire safe place can include a fire resistant lipo battery sack, fireplace, ceramic plant pot, sand box, etc.
Do: Do keep a container of sand nearby when you are charging a lipo battery. Sand is a very cost effective way to deal with a lipo battery fire or explosion. Sand is cheap and effective for these types of emergencies.
Don’t: Do not use a charger designed for a NiCad or NiMH battery for your lipo battery. The radically different charge profile will cause a lipo battery fire.
Don’t: Do not fully discharge your lipo battery. Discharging a lipo battery below it’s minimum voltage limit can cause the battery to fail. Usually, this is not a problem with an advanced electronic speed controller and a minimum voltage cutoff scheme.
Don’t: Do not put your lipo battery in your condo, house, car, etc. after an airplane crash. It is possible that in the course of the crash, the lipo battery may have had some damage, with internal portions of the battery shorting out and starting a chemical reaction that can quickly result in a fire. Put the damaged lipo battery in a fire safe place for at least an hour, and observe for any signs of damage. A battery pack puffing is the main item to look for.
Don’t: Do not puncture a lipo battery cell. If a cell does balloon, be prepared for a fire, and move the lipo battery to a fire safe place for at least one hour. After you have let the cell sit, discharge with a flashlight bulb of a higher voltage than the pack until the light is completely out, then throw the pack away.
Lipo battery conclusion
The advantages of lower weight and much increased motor run times make the lipo battery a clear choice for the radio control electric model airplane pilot. It is imperative, however, that you understand the handling characteristics and technical properties of a lipo battery to ensure your safety, and of those around you. As soon as you think a battery fire “will not happen to my equipment,” you may well find smoke pouring out of your car trunk from an unexpected fire. Be alert and follow the rules!
Author: Gordon McKay