What is LiPo?
We hear the term LiPo so often nowadays we know it refers to batteries widely used almost everywhere: power tools, RC models, toys, and even cars. But what exactly are they? The commonly used LiPo batteries are made of Lithium based electrode and liquid or gel electrolyte in a polymer case. The Lithium based materials makes the electrode able to hold more energy with less weight, and the latest electrolytes are able to make the electrical current flow more freely than before. Also the polymer case allows the battery to be shaped in many formats, so it can be easily fitted in any product. Lightweight, high performance and compact size have made the LiPo battery very popular.
Common RC LiPo
One of the biggest applications for LiPo battery is remote controlled models, like RC model planes, and RC cars. However, there are so many different brands and types, which one is the right one for you? There are some numbers we need to understand first. Capacity, comes in unit of mAh – larger means it holds more capacity and therefore runs longer, very straight forward. Discharging rate is usually marked as “XXC”, like 40C, or 60C. This indicates how fast this battery is able to discharge itself safely, which also translates to how high the output current can be. The C is not for temperature but the capacity amp. For example, a 3000mAh battery with 40C discharging rate will have max output current at 40 x 3000mA = 120A. The voltage is a bit tricky. LiPo batteries all contain single or multiple cells. One cell’s nominal voltage is 3.7v – it can read as high as 4.2 when fully charged, and as low as 3.0v when fully discharged. The voltage may not be marked clearly sometimes, but you will see the count of cell. For example “3S” means three cell in series, which equal to 3 x 3.7v = 11.1v nominal battery output, max at 12.6v and minimum at 9v.
To brushless motors, voltage means RPM, so higher voltage means motors can spin faster. And the total output power can be calculated by the voltage and discharging rate. Last but not the least is the charge rate, similar to discharge rate. This is just an indication of how fast you can charge the battery safely. A lower number means you need longer to charge the battery.
Please note that over charging and over discharging are both very dangerous. Either of them can cause a short circuit and thus result in fire or explosion. So make sure you have a charger which allows you to set the proper charging current and capacity. Also, do not use batteries on devices whose max power consumption is beyond battery’s max output power. Or use an intelligent battery which will regulate the charge and discharge on its own.
Intelligent Batteries. How intelligent they are?
Well, they are just lithium polymer batteries, but the main difference between intelligent and “dumb” batteries is that intelligent batteries have an IBS (intelligent battery sensor) PCB board. This allows users get more information from their battery.
Here are some functions of DJI Intelligent batteries:
- Battery Level Display: the LED indicators display the current battery
- Battery Life Display: the LEDs display the current battery power
- Auto-Discharging Function: To prevent swelling, the battery automatically discharges to below 65% of total power when it is idle for more than ten days. It takes around two days to discharge the battery to 65%. It is normal to feel moderate heat being emitted from the battery during the discharge Discharge thresholds can be set in the DJI GO app.
- Balanced Charging: Automatically balances the voltage of each battery cell when
- Overcharge Protection: Charging automatically stops when the battery is fully
- Temperature Detection: The battery will only charge when the temperature is between 0°C (32°F) and 40°C (104°F).
- Over Current Protection: The battery stops charging when high amperage (more than 8 A) is
- Over Discharge Protection: To prevent over-discharge damage, discharging automatically stops when the battery voltage reaches 12
- Short Circuit Protection: Automatically cuts the power supply when a short circuit is
- Battery Cell Damage Protection: The DJI GO app displays a warning message when a damaged battery cell is
- Battery Error History: Browse the battery error history in the DJI GO
- Sleep Mode: To save power, the battery enters sleep mode after 20 minutes of
- Communication: Information pertaining to the battery’s voltage, capacity, current, etc. is transmitted to the aircraft’s main
*Source: DJI Phantom 4 manual
Apart from DJI’s drones, other popular drones like the 3DR Solo, Xiro and Autel X also use intelligent batteries. For convenience and safety reasons, smart/intelligent batteries have become an industry standard. Unfortunately, Yuneec had no smart batteries on their Typhoon Q500, and considering the cost, they decided not to equip their brand new Typhoon H with them as well. This explains the slightly lower price of Yuneec batteries compared with other brands. However, Yuneec batteries seem a little overpriced compared with other non-intelligent lipos.
All the features mentioned above sound awfully fancy, but their main purpose is safety.
Most of those features prevent internal battery damage. That means intelligent batteries are less likely to catch fire. Circuit shortage, overcharging, over discharging, cell damage, and imbalance can’t be controlled with usual LiPos unless you have a special charger like this:
Always remember to take your batteries off the charger once they’re full!
Incorrect usage of non-intelligent LiPo batteries can lead to the fire or even explosion:
Here is a Charge/discharge time comparison of the most popular drones on the market. I’ve used actual flight times here, not the ones the drone manufacturers advertise.
Note: Charge and Discharge time has nothing to do with “intelligence” of the battery.
Mostly, expensive cells can be charged and discharged faster at higher amperage without causing any harm to the battery. Meanwhile cheap cells also can be charged on the higher amperage but it can shorten the battery life or even cause cell damage.
For that reason most of the RTF drones manufacturers provide optimized chargers for their batteries to keep it as fast and as safe as possible.
Of course a lot of people are still using common LiPos in DIY drones because they are cheap and you can find a battery almost for any configuration.
Meanwhile the Intelligent battery is an advanced technology that makes the pleasure of playing RC even safer than before. In the future, more and more ready to fly drones will be using this kind of batteries. They cost more than the common LiPo, but when it’s all about safety the price of it is absolutely acceptable.
By Tim Levin – A drone enthusiast from Russia, Tim has 2 years experience building industrial application drones for the Chinese logistics company SF Express.