Today I’ll show you how to build a 3 cell battery pack for a remote controlled aircraft. I’ve used 18650 cells and this is really an inexpensive way to get cheap and powerful but also very light weight battery for your RC models.
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Step 1: Be Warned!
Lithium batteries are known to cause fire, burns and even explosions so be careful with handling them. Never ever allow the open terminals of the battery pack to touch each other and do not expose the pack to any mechanical damage. If you do not feel confident in handling Lithium batteries, than please do not try this.
Step 2: Materials
The battery pack consists of 3, 3.7V 18650 batteries that you can buy from pretty much anywhere. These are now common in many devices and are relatively cheap and safer compared to the standard LiPo batteries used with RC models.
Additional they are much lighter so you get an improvement over the standard LiPo battery packs in terms of weight to capacity ratio.
To make it we will need:
Step 3: Solder the Pack Together
We will connect the individual cells in series in order to create the 3S battery pack with a nominal voltage of 11.1V. On the schematic, you can see that we need to connect the negative side of the first battery to the positive side of the second. Then the negative side of the second battery gets connected to the positive side of the third one.
After this we will be left with two free terminal, one positive and one negative, that will be the terminals of our battery pack.
To connect the batteries, I’ve used 5mm wide solder tabs. Ideally you will need to spot weld this contacts but since I don’t have a spot welder available I used solder for the connections. The trick is that you apply the heat for as short as possible in order to prevent damage to any of the cells.
Step 4: Solder the Terminals
On the output terminals of the battery pack, I’ve used 6 mm square wire or the equivalent of around 9 or 10 American Wire Gauge. I know that this is probably an overkill but I thought to better be safe than sorry.
I’ve soldered these wires to a XT60 connector, making sure to keep note on the polarity and I’ve added some shrink tubing on the wires to be slid on to the contacts to prevent any shorts.
In order to properly charge the pack and be able to monitor each cell voltage, we need to add a balance connector. This is an JST-XH 4 pin connector. One wire is connected to the negative side of the battery pack, while the other three are connected to the positive side of each of the three individual cells. This way, the charger can monitor the voltage of each cell and provide balanced charging of the pack.
Before connecting the balance connector, make sure that you identify the proper polarity as marked on the charger balance connectors.
While soldering make sure to trim the excess wires from the connector to provide neat connection.
Step 5: Check the Wiring
Once all of the connections are made, use a multimeter to verify that the expected voltage on each of the pins is correct and that all of the wiring is correct. After that connect the balance connector to the charger and connect the main leads to the battery terminals in the XT60 connector.
The schematic of the pack can be found here.
Step 6: Keep Flying!
The pack will need to be charged with a proper LiPo charger. This way you will not overcharge the individual cells of the pack and avoid damaging them. The charger I have is the iMax B6AC and it works perfectly.
To see the pack in action be sure to subscribe to my YouTube channel for updates on my plane build.
Also make sure to check my other Instructables as well.