Lithium Polymer Battery FAQ(1)

Q1.) Does Temperature Affect Lithium Polymer Batteries?

Yes, lithium polymer batteries are affected by temperature. All batteries use a chemical reaction to provide electricity, and a low temperature slows this reaction down significantly. You cannot harm a lithium battery by running it at a low temperature, but you will notice a significant decrease in performance. Allowing lithium polymer batteries to freeze is generally not recommended, so be sure to store the lithium battery in a cool, dry location over the winter months.

Q2.) How can I calculate theoretical flight time?

In order to calculate the maximum theoretical flight time of your models, you will need to know some information about your battery and motor equipment:
#Motor Amperage
#Pack capacity in Mah (milliamp hours)

After you have that information, you can use the following formula to compute the maximum theoretical flight time of your model:
Time (hours) = (battery capacity (amps) / (motor current (amps)

Notice how the battery capacity must be given in amps. To find your battery capacity in amps, divide the capacity in milliamps by 1000. You will probably want the result expressed in minutes. so multiply the time you just calculated by 60.

By this formula, a 33.5 amp motor powered by a 5000 Mah battery would have a run time of a run time of 8.96 minutes. This is a theoretical maximum, if you actually ran the above set up for the calculated maximum time you would destroy the battery. Most lipo batteries shouldn’t be discharged below 80%, so multiply the calculated time by .8 to account for this.

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The difference between Ni-Cd, Ni-MH, and LiPo

As you know ,there are three main types of batteries currently in use for electric airplane motors. These are Nickel Cadmium (NiCad), Nickel Metal Hydride (NiMH) and Lithium Polymer (LiPo).

Dou know the difference between Ni-Cd, Ni-MH, and LiPo this three type of batteries?


Li-polymer Battery
LiPo (Lithium Polymer). This is one of the newest cell types available. It is also the lightest battery type currently available on a commercial basis and can provide more power than the other main cell types. There are no known problems of memory effect with this battery type and it is the easiest battery type to care for. The downside of this battery is that it has the highest engineering costs and therefore the price is usually considerably higher than other cell types.


Ni-MH Battery
Ni-MH (Nickel Metal Hydride). This cell type is the most common cell type currently available for laptop computers, (although Li-ion is rapidly becoming the most popular) This battery type is relatively cheap to manufacture and therefore tends to be cheaper than Li-ion. This cell type is prone to 'memory effect' so it is important to take good care of your Ni-MH battery to ensure that you obtain the best runtimes.


Ni-Cd Battery
Ni-Cd (Nickel Cadmium). This is one of the oldest cell types and is generally only found in older laptops. The main pro for this cell type is its ability to handle higher loads, and therefore is more commonly found in portable power tools or devices that need a lot of power to work efficiently. The main downside of this cell type is that it is notorious for suffering with memory effect so good care must be taken with this battery to ensure most effective use of battery.

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What Battery should I use?

What Battery should I use?



When in doubt, use your airplane manufacturer’s recommended battery. This is generally a good starting point, although with experience you will probably have your own ideas about the best battery to use. Here is some basic info about battery types.

There are three main types of batteries currently (no pun intended) in use for electric airplane motors. These are Nickel Cadmium (NiCad), Nickel Metal Hydride (NiMH) and Lithium Polymer (LiPo).

NiCads are the oldest generation of these batteries. They pack more power but are heavier than the NiMH. The NiMH voltage (power) tends to fall off fairly fast during the flight. The wonder batteries LiPos have great power for little weight and hold that power well throughout the flight. However, LiPos tend to be much more expensive than NiCad or NiMH. Again, go with the recommended battery, you will have time to experiment after you learn to fly.

Note that more cells in the battery means more voltage, which means more power.

Power (Watts) = Current (Amps) x Voltage (Volts)

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RC Lithium-ion Polymer batteries

Let you can learn more about RC Lithium-ion Polymer batteries

LiPo batteries are very different from previous generation batteries and understanding how they work, and especially how to charge them, is the key to getting the best performance.

Series
Individual Lithium Polymer cells have a nominal voltage of 3.7 volts (vs. 1.2volts per cell for Ni-Cds or NiMHs). Cells are wired in series to give the following pack voltages:
1 cell = 3.7 volts
2 cells in series = 7.4 volts
3 cells in series = 11.1 volts

Parallel
Unlike Ni-Cd and Ni-MH batteries that self-discharge when wired in parallel, LiPo cells can be hooked up, charged and discharged in parallel with no detrimental effect. Wiring two LiPo cells in parallel doubles the capacity (more run time), plus an important advantage of wiring in parallel is that each cell only sees half the total current.

3S 2P
A battery pack that has three cells in series (giving 11.1 volts) and 2 of these 3-cell packs are wired in parallel is commonly referred to as a 3S, 2P (3 series, 2 parallel).

C Rating
LiPo cells are also commonly given a C or current rating. This is the maximum average recommended discharge current for the cell. For example, the VP2150/20C packs have a 20C rating. To determine the maximum recommended discharge rate multiply the capacity times the C rating. 2150mAh x 20C = 43,000. So the maximum recommended discharge rate would be 43,000mA or 43 amps. If your application has a higher amp draw, remember that LiPo cells can be wired in parallel, and with 2 cells in parallel each cell sees half the total current. With 3 cells in parallel, each cell see one third the current.
By wiring packs in a combination of series to get the voltage and parallel to achieve the capacity and individual cell current to an acceptable level, LiPo cells can be used to power nearly every type and size of model.

Charging
Charging LiPo batteries requires a very different charge method than other types of cells. It's imperative to use a battery charger designed specifically for LiPo batteries, and with most LiPo-specific chargers it's necessary to correctly select the cell count (1, 2 or 3 cells) manually.

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