Best Lipo Charger - Lithium Polymer Battery Charger Buying Guide
Lithium Polymer batteries are used in nearly all electronic devices nowadays. Flying drones or other radio controlled toys can be a lot fun and most of these gadgets run on batteries. All this fun wears out if your quadcopter’s batteries run out. You can have extra batteries, but if the batteries take too long to charge and can’t retain the charge for at least a while, it will not make for a pleasant experience.
Luckily, today you can buy specialized battery chargers that can charge your drones’ batteries fast and have the capability to charge more than one battery. You can even get chargers that will charge different types of batteries.
If you fly a quadcopter, you should have a USB multi charger with you so that you can charge multiple battery packs at a time. You can connect multiple battery packs to this multi charger (a little box) first. Then the USB cable with this box is connected to a wall charger. It may take up to an hour to get the batteries fully charged but you get more flight time too because all the batteries are all charged together.
If you looking for a protection bag to save your batteries from overcharging or overvoltage LiPo safe is the answer. The material used in these lipo battery bags is burn proof and can hold fire.
You would want to pack the batteries in LiPo safe before you connect the charger.
Gone are days of NiCD (nickel cadmium) or NiMH (nickel metal hydride). But if you are still using these batteries, you need not despair. All types of batteries (NiCD, NiMH, LiPo, LiFe) can be charged by the chargers on the market.
Before going ahead with selecting a charger I will list out the specifications you have to look for in a charger. We will see them in detail even though some of them do not need much explanation.
Lipo chargers - What to look for
- Number of cells the charger can support
- Output charge rate in Amps
- Types of cells the charger can support
- External vs. Internal power supply
Number of Cells
There will be a limit on the number of cells the charger can work with. Some chargers may support 6 or even 8 cells at a time. However, they may not be able to charge only one cell. So before buying a charger you would want to check the number of batteries supported by the charger.
If you look at computerized RC chargers, most of them can charge up to 6 LiPo batteries and 15 NIMH or NiCD cell packs.
Have you heard about “2S’ battery pack? This means 2 batteries connected in series. Usually, a LiPo battery’s nominal voltage is 3.7V. For a “2S’ pack the voltage will be 7.4 V (3.7V * 2 = 7.4V) and for a three-cell pack, the voltage will be 11.1 V (3.7V * 3 = 11.1V).
What is nominal voltage? It’s the default voltage of a cell when it is resting. A LiPo battery can reach up to 4.2 V when it is fully charged. But the safe minimum voltage of the battery is 3.0V. Hence, 3.7v is considered as the nominal charge because that is the average voltage value.
Charger power in Watt
The power mentioned in Watt represents the maximum output value and hence that is the most important value you should check before buying a charger.
The power is calculated in watt and the formula is voltage (Volts) x current (Amps). If the power requirement is not met by your charger your battery will get recharged in a low current.
Which means if you want to recharge three 2000mAh batteries at 12.6 V and 2A (1C), the power of the charger should be 25.2 watts. Likewise to charge these three batteries in 4A (2C) the power should be doubled that is 50.4 Watt.
As the cell count varies, the maximum current also varies. So you have to be careful that it does not exceed the charge rate of the charger.
Let me explain. The 50W charger that you bought has a maximum charge rate of 5A. If you charge a 3S LiPo the real charge rate can become only 4A (4A=50W / 12.6V). But you should not charge a 2S LiPo battery because the maximum rate of charge current will become 6A (6A=50W / 7.4V) and your charger cannot support that. Consider the capacity of your battery also before buying a charger for your battery.
Above given situation does not consider the efficiency loss of the charger while charging. Here I am assuming the loss will be between 10% and 20%. In that case, you will need a 60W charger.
If you are planning for parallel charging even 60W may not be enough. You can calculate this and you will understand that higher the charge power better the efficiency of the charger. Finding out the ideal charger power for your cells is not rocket science you just need to do some simple math. Look at the example given below.
Battery Capacity = 2200mAh ; Number of batteries = 6 3S batteries ; Charge rate needed per battery =1C
Maximum current rate =1C x 2200mAh x 6= 13.2 A
Hence the power needed for your charger = 13.2A x 12.6V x 120%= 199.6W
Here, the ideal charge rate of the charger will be more than 200W and the maximum charge current is 14A+.
A charger with lower power also will work but it will take a long time for your batteries to be fully charged.
‘C’ rate is used to represent a LiPo battery’s charging rate (‘C’ denotes capacity). But mAh is widely used to express the battery capacity. Actually, mAh is the unit used to represent electric charge that is calculated using the formula – current (mA) x time (Hours).
Four factors that control your charger’s current rate are:
- Charger’s maximum charge current rate
- Battery’s maximum current charge
The recommended current rate of LiPo batteries is 1C however; there are some LiPo batteries that are capable of fast charging (2C or higher). These batteries are expensive.
Having said this, it is always safe to charge your LiPo batteries at a lower rate. This will increase the battery life and will prevent the battery from becoming too hot. We will discuss about disposing broken and old LiPo batteries later.
The charge current needed to charge a 3S 2000 mAh battery is 2A (1x2000mA). If you want to charge the same battery at 2C the current needed is 4A (2x2000mA). So if the capacity of the battery is 5000mAh you will need 5A charger current.
You can check the manual of the charger to find out the maximum charging current and rate. Consider this when you buy a charger for your LiPo battery because a charger with a lower rate will take more time.
In some instances your charger and your battery both may support 6A charging rate; However it is not necessary that the battery will get charged at that rate. Other factors that will influence the charging rate are number of cells and power of the charger.
This is very simple. For your LiPo batteries, you have to buy a charger that can handle LiPo batteries. The charger should know the way to interact with your LiPo batteries or else the charger may cause a fire.
You will also get chargers that support multiple types like NIMH and NiCd other than LiPo.
The main advantages of LiPo battery over the NiMH (Nickel-Metal Hydride) or NiCD (Nickel Cadmium) batteries are:
- They are lightweight and are easy to manufacture in any shape or size
- They can be made in higher capacities because they can contain more power than other two types
- LiPo batteries are capable of high discharge rate
Now let us see what are the disadvantages of LiPo batteries:
- These batteries have a shorter lifespan when compared to other types
- The average number of cycles is 300 to 400
- The chemicals used to make LiPo batteries are very sensitive; the battery could catch fire if they are physically damaged. You would never, ever want to use a lipo battery that you suspect has been physically damaged.
- When you charge, store, and discharge LiPo batteries you have to be very careful
- The accessories used for the maintenance of LiPo batteries are expensive
External vs Internal Power Supply
Here we are going to discuss about the power source to the charger. There are chargers that come with an internal power source and you can see chargers with external power source too in the market.
If the charger has an inbuilt power supply you may have to settle for a 50-watt charger because they cannot integrate more powerful supply within the charger box. If you need more power you will have to buy a more powerful supply (350+ Watt). But the benefit of having the USB charger is that you can modify any supply that can provide you 250 watt can and use it as the external power source.
But you do not have to worry as all computerized battery chargers are manufactured to accept the charge (12-14 VDC input) from a flight box battery or automobile battery.
You can even see chargers for RC battery that can work on 30+V DC charge. This is useful if you want to recharge battery packs with higher voltage and watt ratings. These high powered battery chargers can also be used for lower voltage charging.
Another category of chargers come with both inbuilt power supply and external power supply support. These can work with an input of 12 V DC and also support a 120 AC household power supply (built-in). But the main issue with this built-in power supply is that this will work with only 50-60 watt chargers.
Here the size is a factor to be accounted for - the charger will become much bigger if you wish to integrate a more powerful supply.
For example, if you want to keep on supplying 100 watts at a rate of 14 V DC you will need much bigger supply. In fact, it will be much bigger than the charger itself. Another fact that you have to consider is the heat that is emitted from these bigger power supplies. To compensate this you will have to add heat sinks and cooling fans making it even bigger.
Additional features are always good to have but are not mandatory for the performance of your charger. Keep in mind that the more features your charger has, higher the cost will be. There are three types of additional features that can be availed by you. They are basic features, safety features, and advanced charger features. It's always a good idea to use a lipo battery tester, monitor and use only appropriate connectors to connect cells in the battery.
Basic features you would want to have in a LiPo charger
- The option to see each cell’s voltage while charging
- The addition of charging functions for LiPo battery like balance charge, discharging, and storage
- Before starting the charging if you can confirm the cell count you can prevent an accident that may be caused due to the use of the wrong charger type
- Protection for overvoltage and under voltage scenarios
- Option to detect temperature and limit the maximum temperature
- Facility to set a timer for charging
- Support for multiple types of batteries
- Monitoring internal resistance of the battery and cells
- Advanced programming so that you can pre-set the values (like charger rate) for each LiPo battery
- Capability to connect to a computer so that you can monitor the voltage level, the charging current (of each cell and battery), time and more.