Lithium Polymer batteries (LiPo, Li-Poly) are now the most common form of re-chargeable battery used in the RC hobby world, especial for remote controlled helicopters. But how do you go about choosing the correct lipo battery pack for your helicopter? There are a number of factors to consider:
Capacity and Weight
- This is the primary factor that decides flight time, taking the weight of the machine and the amount of power drawn by the motor is taken into account. This is measured in mAh (milli-amps) with higher counts meaning higher the prices and a heavier battery. The key is to find a good balance between the mAh you require and the weight of the battery to ensure optimum flight time.
Voltage aka Cell Count
- Lithium batteries have 3.7 volts per cell, for example a 3S lipo battery is 11.1V. Most power systems require a specific voltage to operate, with more advanced ones running on a lower voltage for efficiency and a higher voltage for more power. Make sure you use the correct voltage/cell count for your system.
- This is the internal resistance of the battery, basically the amount of power that can be drawn from the battery over a certain length of time. A higher C rating means the battery can provide more power faster. Again, generally the higher the rating the higher the price. For beginners this not to important, however for more advanced flying where the motor needs to draw a lot of power for fast, powerful manoeuvres, this becomes much more important. More expensive batteries will have a standard C rating and a ‘burst’ C rating, for example 35C/45C (burst), this means that the battery will provide 35C normally, and can provide a 45C short boost if needed.
Charge C rating should also be considered. Today with more advanced lipo chargers available, lipo batteries can be charged significantly more quickly. Look out for batteries with a 5C charge rating – this is currently the fastest available and with a capable charger will give you about a 90% charge in 10 minutes.
- Common types of connectors include JST - used mainly for lower voltage batteries, Deans – used for batteries of higher voltage. Adapters can be used to mix and match these connectors. Gold Connectors are used for higher end power systems. They come in various different sizes and you are generally left to decide which to use, as most lipo battery packs come with bare wires so you can solder on your preferred connectors.
- The lipo battery packs can come in a variety of different shapes and configurations of cells, this depends on manufacturer and if they were designed for a specific RC helicopter. Getting the right shape battery to fit your frame can save a lot of headaches and modifying, if possible always go with batteries recommended for you machine, as they are guaranteed to fit.
Lifetime and Quality
- How many re-charges a lipo battery can take is often not considered when buying, however it should be. Better quality (and most likely more expensive) packs will last longer, sometimes taking up to 10x more re-charges than a lower quality counter part. Better quality raw materials go a long way to better performance and lifetime, as well as how they are made (machine or hand). Be sure to look closely at these stats when choosing your lipo packs. And remember never to over dis-charge a lipo pack, as this will damage it and reduce its lifetime further.
A good quality charger will also go a long way to extending the lifetime of your batteries and some are also able to repair damaged packs as well as providing extensive safety features. Lithium batteries have been known to burst into flames if safety, quality and using the correct chargers is not taken seriously.
Finally, a word about the future of batteries for electric powered rc helicopters. Currently flight is at a maximum of about 15 minutes. Battery technology is currently moving forward at a very fast rate, with the advent of fuel cell technology and various other innovations such as Lithium-Air we can expect to see Lithium batteries become much more efficient, powerful and safer within the coming years.
Keywords: Lipo Batteries