In this article we will look into how to choose LIPO battery charger, and hopefully it should give you some idea in picking the best LiPo charger for multicopters.
When buying a LiPo battery charger, it would be easier if you could just walk into a hobby shop, and ask the staff what charger you should get. However if you are getting it online you are pretty much on your own. Therefore researching beforehand, knowing what you need and what options available are very important.
Choosing The BEST LiPo Charger for Quadcopter / Multirotor
We have talked about how to choose the best LiPo Battery capacity for your quadcopter build. We have covered most areas in building and flying quadcopters, but LiPo charger is rarely mentioned. In this post, we will go through some of key factors in selecting a good LiPo battery charger, for your quadcopter and other multirotors.
These are the important consideration when choosing the best LiPo charger.
- Technical Specification of a LiPo charger
- Extra Features
- Choosing Power Supply for Lipo battery charger
- Quality and Cost
Technical Specification of a LiPo Charger
There are non-programmable charger which are “plug and charge”. You just need to plug your battery into these charger, and it will start charging, no input from the user is needed. These might seem simple, and economical too, but they are very slow in charging, and you can’t change any of the settings and options.
High quality chargers nowadays are almost all computerized and programmable. A programmable charger allows you to set all sorts of parameters, such as charging current, type of batteries, charging period etc. They show you the battery condition such as what the voltages is each cell, how much current has been charged into them and so on. It basically manages the charging for you in the way you want, ensuring the batteries are charged safely and accurately.
Some of the programmable chargers also do clever things including, adjusting charging current depending on charger temperature, auto-detecting battery cell counts and battery voltage level. You can even discharge your battery for storage with some programmable chargers.
LiPo Battery Cell Count Supports
There are maximum and minimum LiPo cell count, the battery charger can handle. For example some battery charger supports up to 6S, some even up to 8S, but they might not be capable of charging 1S LiPo. Make sure you know what cell count the charger supports.
Charge Current Rate
The charge current rate is limited by three factors:
- Max Charge Current of your LiPo Battery
- Max Charge Current rate of your charger
- Charger Power and LiPo cell count
LiPo batteries are often recommended to be charged at 1C current rate for various reasons, although some more expensive LiPo batteries these days are advertised as fast charging, which can be charged at 2C or even higher. The main reason for charging at lower current is safety, and to prevent the battery gets too hot, which might cause the battery to go “puff” and shorter battery life. Here we discuss how to dispose old and broken LiPo batteries.
Basically, to charge at 1C, it means if you have a 3S 2000mAh LiPo battery, your charge current would be 1 x 2000mA = 2A; But to charge at 2C, the charge current is 2 x 2000mA = 4A.
When choosing a battery charger, The manual should specify what the maximum charge current is. If a low charge rate charger is used, charging will take longer. It’s completely fine if you don’t mind spending more time waiting.
Sometimes the charger might say the max charge current is 6A, and your battery is also fine to be charged at 6A, but it doesn’t necessary means you are able to charge at this rate. It also depends on your charger power and the cell count of your LiPo battery. In the next chapter we can find out about why and how to choose charger power wattage.
LiPo Charger Power is measured in Watt which is calculated by multiplying voltage (Volts) and current (Amps). If your charger does not meet the power requirement, you might find it charge your battery at a lower current.
For example, to charge a 3S 2000mAh LiPo at 12.6V at 1C (2A), you will need a charger that are rated for 25.2 watts (= 12.6V x 2A). So it’s clear that if you want to charge at 2C (4A), you will need double of the power which is 50.4W.
Note that when dealing with different cell count LiPo, the max charge current also varies, but it should not exceed the max charge rate of your LiPo charger. For example for a 50W charger that has a 5A max charge rate, for a 3S LiPo, you will find the actual max charge current can only be around 4A (= 50W / 12.6V). But for a 2S battery, the calculated result is now nearly 6A (= 50W / 7.4V). But you shouldn’t charge at 6A, because the charger is rated for max 5A . Of course, you need to take into account the battery capacity as well to determine the charge rate the LiPo can take.
This is so far only a ideal estimation, there is also efficiency loss with the battery charger when charging, so you definitely need higher wattage than the number from above calculation. I usually assume the power loss is around 10% to 20%, so if you are looking at 50W, a 60W charger is a good choice IMO (50*120%).
Although it might seem low wattage chargers like 50W or 60W is good enough, but as you move up in cell counts or start doing parallel charging, you will realize how much better a high power battery charger is. To calculate what a suitable LiPo battery charger spec should look like for parallel charging, we can do some simple maths.
For example to charge six 3S 2200mAh LiPo batteries at 1C at the same time, the max charge current requirement for your ideal Charger is 1C x 2200mA x 6 = 13.2A. And the power can be calculated as 13.2A * 12.6V * 120% = 199.6W. In this case, I will get a charger that is rated for 200W+, and max charge current of 14A or more (This is only a theoretical estimation, it might differ in reality situations). Of course a lower power charger would work too, but your charging will take longer as it can’t deliver that much charge current.
Types of batteries supports
Some chargers supports many other types of batteries apart from LiPo, such as NiCad, NIMH, PB. It might come in handy at some point, but since I am only interested in multirotor applications which only uses LiPo, I don’t really care that much.
You probably don’t need all of the following extra features, but they are good to have. The more features it has, the more expensive charger it’s going to be.
Some basic charger features
- Backlight LCD display.
- Shows voltages of each cell when charging.
- Precise voltage reading of 0.01 – 0.02 volts.
- LiPo charging features such as discharging function, balance charge function and LiPo storage function.
Some Safety features
- Cell count confirmation protection before charging.
- Over and Under voltage protection.
- Temperature detection and limit setting for overheat protection.
- Time out feature (stop charging after certain period of time).
- Warning buzzer.
And more advance LiPo charger features
- Support many rechargeable battery types.
- Measuring Internal Resistance of each cell and the entire battery.
- Profile programming for LiPo of different capacity and cell count, so you don’t have to set up parameters like charge current etc everytime you charge them.
- Computer connection and GUI. Some high end charger allows you to connect your charger up to your PC, so you can see realtime data like charging current, voltage level of each cell, time remaining etc. On some of them you can even update charger firmware too..
Choosing Power Supply for Lipo battery charger
If the charger doesn’t have a built-in power supply or come with an external power supply, it mean you will have to buy one separately. A decent power supply can cost quite a lot, sometimes are as expensive as the charger itself. They are chunky and heavy. I guess the reason they are being sold separately, being the weight and size of the power supply can cost them more to pack and ship. And indeed the transformer weights a lot given the power they have to provide.
The charger will specify what the input voltage should be, and your power supply should have an output voltage that meets the requirement. The power supply also need to provide enough power for the charger. The power supply power is calculated by multiplying output current and output voltage.
For example, for the Turnigy Accucel-6, it’s rated at 50W, and input voltage is rated at 11V-17V. To match it, this power supply would be adequate. The example power supply’s output voltage is 15V, which is meets our voltage requirement. It can output 7A current, 7A x 15V = 105W, which is more than enough (always leave plenty rooms in case of over heat issues). Again, this calculation is only estimation, it gives you an idea what power supply to look for. However I would recommend to consult the professionals from the online shop, to confirm that it meets your requirements before hitting the buy button.
Charger Quality and Cost
A LiPo charger should be treated as a long term investment when you start out in RC hobby, just like your radio transmitter. So expect to spend fair amount of money on the quality chargers.
The most expensive charger is not necessary the best, but a good quality charger comes with reasonable price. My advice is, don’t look at the how much it is before you figure out what you actually need. List your requirements on a piece of paper, and find the chargers that you are happy with. If you don’t need the “fancy features”, then don’t add it to your list.
If you don’t find anything suitable locally then try shopping abroad, It offers you more options with lower prices. Most of the chargers you find will probably be made in China or other countries. It’s a stereotype that China always make bad products, not necessary true. In fact most RC products are made in China these days, including some really top notch brand names.
Picking a LiPo battery charger is just like any other quadcopter parts, it’s quality versus price. But unless you actually try in, you won’t know how good or how bad it is. So read some other guides on how to choose a LiPo battery charger, ask on forums, do your research, and make sure you have a good understanding of LiPo charging before making your decision. This article is based on my personal experience, if there is any error or missing info please let me know.
Further Reading: How to start out with Quadcopter – Beginner guide.