In this instructable I will be building a small PCB board to parallel charge small 3.7v 1S LiPo batteries, the type commonly found in RC toys such as quadcopters. These batteries generally have low capacity and do not have more than one cell. Bigger, multi-cell batteries are outside the scope of this instructable as a further board for the balance lead needs to be made.
I needed to charge some 1S batteries and didn't want to wait for a pre-fabricated charging lead or board to arrive in the post. I do lots of Arduino stuff so found that I could use modified PCB headers to create my board.
The advantage of this design is it works with several types of connector. I am using it for mini-JST and micro-Losi (also called Walkera) connectors. I will also test it with micro-JST, once those batteries arrive. If you use similar capacity batteries but in various polarities (normal Turnigy accucell batteries and the "fits nine eagles" versions with opposite polarity) you can charge them together as long as you match all the + and - wires.
A parallel charge board is usually used by a suitably experienced person in conjunction with a hobby grade battery charger. Before materials are gathered you should make sure you know what you are doing with LiPo batteries. Particularly how to handle them, store them and charge them. There are many good resources online.
If you are building this parallel charge board you can easily short the batteries (bad!) or connect them in reverse polarity (also bad) if you are not careful while building, or are not certain about safe use of the board.
Step 1: Required Materials
To create this board you will need:
- PCB headers
- a file
- soldering iron + solder
- some wire, or the appropriate connector (e.g. banana or EC3) for your charger
- some stripboard
- some way of testing continuity
It may also help if you have:
- a vice
- a multimeter
- some wood to pad the jaws of the vice
- a red marker pen
- a black marker pen
Step 2: Pop Out the Header Pins and File Them Down
When I went to look for some things to make a parallel charge board out of, I found PCB headers. These are ideal as they are male, and LiPo battery connectors are mostly female by convention.
The spacing is also perfect for mini-jst and micro-losi connectors.
What is not perfect however is the thickness. The header pins are too thick to fit the connectors. I got around this by filing them down so they are thinner. I took approximately a third (33%) of the material off. You may make mistakes, so file down a few more header pins than you plan to use.
Remove the pins from the header using pliers.
Once removed, file them down so that the part which will protrude from the header, and connect with your battery, is around 1/3 (33%) thinner.
I used a vice and some wood to hold the pins in place. My file was on a multitool. I had some problems with the pins becoming tapered to a point (thinner toward the top,but wide at the bottom). I adjusted my technique to file with more pressure at the bottom and they came out straight.
Step 3: Test the Header Pins in Your Connector
I filed down 10 pins (I needed 8 for the charger as I was going to charge 3 batteries in parallel).
Take those pins and test them on the appropriate connector - if this connector is attached to a battery be careful to only test one at a time and to avoid short circuiting the battery (bad!)
Put the ones that fit well aside to be used in the next step. Discard the others.
Step 4: Solder the Charger Connectors and Headers to Your Stripboard
Now you have selected the headers that fit your connectors well, it's time to solder them to the stripboard.
First solder the wires for your charger plugs to the stripboard. You want to arrange the stripboard so that you have one strip for negative and one for positive (see pictures).
I soldered my headers in quite widely spaced, but did not need to. Make sure you space them so you can plug in all your connectors.
Is is very important with LiPo batteries that they are not shorted out. We will test for shorts later, but when soldering be careful not to bridge between your positive and negative tracks.
Step 5: Test Your Board
To be doubly sure the wires and headers are soldered properly, grab something to test your circuit with (I used a multimeter).
To avoid battery mishaps (bad!), and ensure correct functioning you must ensure:
- There is no connection between the positive and negative pins or wires; and
- The header pins on each side are connected to the correct wire without any significant resistance (which would indicate a badly soldered joint).
At this stage consider insulating the bare solder on the back of the board - you could use electrical tape, non-conductive hot glue or similar.
All good great - let's connect up.
Step 6: Connect Your 1S Battery / Batteries (the Right Way Round!) and Go Charge
Now the board has been made and tested, connect up the battery (or batteries) you want to charge, and connect the board to the charger.
These header pins can be connected in any orientation, unlike the male mini-JST or micro-Losi connectors which only connect the correct way, So... there is a risk here that you may inadvertently connect a battery the wrong way round (bad!).
Make sure all the red wires are on one side (the side with the red lead going to the red or positive port of the charger), and all the black wires are on the other side (the side with the black lead going to the black or negative port on the charger).
Most hobby grade chargers will let you know if an individual battery is the wrong way round, but when using multiple batteries it may not be able to tell if one of six is the wrong way round so be careful.
Double check all your wiring again (red to red to red, and black to black to black). To assist me in not shorting my batteries (bad!) I later coloured the red side of the board red, and the black side black with permanent marker.
Dial in the settings for your charger and away you go. Happy charging!