October 21

Lipo Battery Charger

Typical Lipo Charger

Typical Lipo Charger

I am going to try to explain, in as simple a way as possible, how a Lipo Charger fills each battery cell with its maximum safe charge capacity.

RC Lipo battery cells hold a full charge voltage of 4.20v. A special charging method know as CC/CV ( Constant Current/Constant Voltage ) is required in order to squeeze every last ounce of current  into the cells.

Let me remind you that Current is measured in Amps (1 Amp = 1000 Milliamps).

You will see that by convention Lipo Batteries usually carry a capacity designation measured in Milliamp Hours (MaH). This means that the battery can deliver its rated capacity for one hour.  I can only imagine that lipo manufacturers catering to the Radio Control market felt that purchasers would be more impressed buying a 3000 MaH lipo than one marked up as a 3AH (3 Amp Hour) lipo. Both mean the same but the former sounds far more impressive and powerful than the latter.

Phase one of the charge process is called Constant Current ( CC ) and is the same process used to charge NiMH and Nicad batteries. The charger supplies a steady flow of current into the cells which in turn pushes the voltage level up toward the maximum of approximately 4.20v. During this phase the charger occasionally drops the charge current and checks that the cells are holding their voltage. As the cells gradually fill up, the voltage they hold will increase, and so the voltage the charger supplies will gradually decrease.

Once the cells are holding close to their maximum rated voltage the charger switches to Phase Two of the charge process. This is known as Constant Voltage ( CV ). A steady voltage is now supplied to the cells to sustain the correct level whilst the current is gradually reduced. The charger continues to check every so often to see that the cells are holding their voltage. This will continue until all the cells are holding 4.20v ( give or take 0.02v ) and then the charge will finish automatically.

During the charge cycle the charger will also remove excess voltage from any cells that are above the level of the other cells. This keeps them balanced & charging at the same rate and as a consequence is known as balancing. If you buy a modern Lipo charger it will invariably include a balancing facility. There will be a set of white sockets positioned on the charger close to the main connector lead sockets into which you can connect the small white balance connector coming from your lipo on a separate lead. Be sure to connect this lead to the correct sized socket on the charger.

I have attempted to make this explanation as simple as possible so that you can understand how things work. Again, don’t worry too much if it is not totally clear to you. Just accept that you will need one of these special chargers for you lipos and take time to understand the instructions for connecting up and charging you lipo batteries. Don’t be frightened to ask for help from your fellow club members ( if you have them!) or someone who is familiar with lipo charging.

Lipo chargers come in a variety of formats. The simplest is one that is designed to be powered from a 12V to 18V DC supply. This may be a mains AC to DC converter power supply or a spare car battery or leisure battery. Leisure batteries are preferable as they are designed for continuous use whereas car batteries deliver high current for short periods of time typically when starting a car.

Some people use the car battery on the vehicle they use for transportation to their flying site. I do not recommend this approach as continuous lipo charging at the field could render the battery incapable of restarting the vehicle at the end of the flying session.

Other types have an integrated mains power input to DC converter plus a socket to attach an external DC supply. Others have more than one charge output so that you can charge two or more lipos at the same time.

I would suggest at this early stage a simple, single output, charger capable of being powered by either mains or a 12V dc supply and designed to supply 50 to 60 watts of output power. Such a charger will be more than adequate to charge the lipo you will be using  in your trainer and can be used at home or at the field.

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