Building an RC battery with Maker Battery modules is surprisingly easy. Just follow the steps below to build your own RC battery!
Step 1: Measure module voltage
Start by measuring the voltage of all of your cell modules to ensure that they’re all more or less identical. They can be off by a few hundredths, but any more than that might indicate that one or more cells have an issue. This is incredibly rare as these cells are checked at the factory and then double checked before shipping, but this triple check is just one last step to ensure that you’re building a top quality battery.
Step 2: Layout your modules
Now you’ll begin your module layout. This will determine the final size and shape of your battery. For most applications a simple linear pack is preferred. If you have a specific battery box that you’re trying to fit your battery into then you might want to get a little more creative with your arrangement.
Generally speaking there are two different straight layout methods: straight packing and offset packing.
Straight packing with result in a narrower yet longer battery, while offset packing is a bit wider yet smaller overall volume. This is because offset packing is a more efficient use of space, leaving less dead air space between the battery cells.
For this tutorial we are going to use straight packing to give us a narrower yet longer battery, but the same steps apply for either method so feel free to use offset packing if you’d like.
When you arrange your cells, make sure you set them up like in the picture above with alternating sides facing up. This will make it easier to perform your series connections later on.
Now go ahead and hot glue your modules together into the correct orientation. Use a decent amount so you have a good connection, but you don’t have to drown your modules in glue either. These are fairly light weight packs so there isn’t a lot of stress on them from their own weight.
Step 3: Label your modules
You can use the + and – stickers in your Maker Battery kit and/or a marker to label the positive and negative ends of your modules as well as to number the cells. These module numbers will help you keep track of the modules later on when you’re connecting the balance wires. These stickers and labels aren’t 100% necessary, but they can be a nice help when you’re performing the critical series connections. I recommend not skipping this step.
Step 4: Tinning the modules
In order to solder your cell modules together you’ll first need to tin them. For this process you’ll need two things to ensure good tinning: a good 60W or higher adjustable temperature soldering iron and some quality 60/40 lead electrical solder. Don’t skimp on either. A decent soldering iron can cost $15 and good solder another $10. They’re both worth it. You want to spend as little time heating the cell modules as possible and to do that you need a strong soldering iron that can transfer heat quickly. A weak soldering iron has to sit on the nickel for a long time, which ends up transferring all the heat to the cells. You want just a couple seconds of contact.
To tin the nickel, touch the tip of your soldering iron to the nickel in between the cells and then touch a piece of solder to the point between the soldering iron and the nickel. You’ll see the solder melt and then within another second begin to blend into the nickel strip. At that point you can remove the soldering iron and move to the next point.
Make sure that you’re soldering on the point in between cells and not directly on top of them. The nickel will heat and tin faster in between cells and that point will also keep the heat as far from the cell as possible.
Step 5: Cutting the nickel strips
Now find your roll of nickel strip and open it up. Be careful not to let it get away from you and short circuit your battery terminals.
Cut the first few pieces of nickel strip to approximately 3/4″ or 2 cm in length. You don’t need to measure them out exactly; just eyeball it. They should be long enough to span from one solder blob to another on two consecutive modules.
You can use any ordinary pair of scissors to cut the nickel. Depending how you hold the nickel when you cut it, you might find that you get funny corners that turn up at a sharp angle. If this happens, just push the corner against the table to flatten it back down. It’s not a major problem, but the sharply bent corner can sometimes catch on your gloves and cause you to accidentally drag the nickel away from where you intend to place it. It’s more of a problem on the backside of the battery once you’ve already done the first set of series connections. At that point it’s easier to accidentally cause a short circuit on the backside of the battery.
When you cut the nickel strips, you’ll probably notice that they make a slight arc from the shape of the roll. I like to place the nickel strips on the modules with the arc facing down like a rainbow. This keeps the two ends on the solder blobs. If you do it the other way and place the nickel strip down like a bowl it may rock oddly.
Step 6: Soldering the nickel strips
Below you can see the wiring diagram (or nickel strip diagram since we aren’t using wires yet) for the 5s RC battery pack we are making. It is very important that you do these series connections correctly. It’s quite easy to accidentally lay a piece of nickel strip on the wrong connection and cause a short circuit, so pay attention and double check before you lay down each piece of nickel.
When you solder the strips, the name of the game is just like during tinning: try to spend as little time heating the modules as possible. The whole soldering operation should take about 2-3 seconds, though you’ll get it down under 2 seconds with some practice.
This is also where that chopstick, popsicle stick, tooth pick, matchstick or other piece of wood is going to be used. The soldering procedure I use is as follows:
- hold the chopstick in my mouth (easier to reach when switching it to my hand)
- put the nickel strip onto the module so it overlaps the solder spots I previously tinned
- hold the soldering iron in my right hand and solder in my left hand (switch if you’re a lefty)
- place the tip of the soldering iron on the edge of the nickel strip to heat it while contacting the solder to the soldering iron and the nickel strip
- merge the module’s pre-tinned solder blob into the new solder blob that I just put on the nickel strip
- simultaneously while merging the solder blobs, drop the solder and pick up the chopstick with my left hand
- use the chopstick to hold the nickel strip down while removing the soldering iron and hold until cool
You’ll want to solder the first two series connections between +1 and -2 and then the second series connections between +3 and -4. However, that’s only two strips of nickel for each series connection. Each strip of nickel can handle about 7.5A and so to get our full 30A current carrying capacity we need four strips. So to get four strips we will simply solder two more strips right on top of the connections we already made. Each connection will be two sets of two stacked nickel strips, as shown in the photo below.
After you’ve finished this side of the battery, you’ll need to turn it over and work on the back side. That’s where you’ll connect the “gaps” that we left on the top side of the battery, such as from +1 to -2 and +3 to -4. Be very careful though that you don’t complete any connections that are already completed on the other side of the battery. Look at the wiring diagram at the top of Step 6 again to see which connections you need to make. Notice how if a connection is made on the top side of the battery, it is left open on the bottom and vice versa. This way we are always wiring the modules in series. Your final connections should look like this:
Step 7: Adding the wires
Now we’ll add the discharge and the balance wires to the battery. Let’s start with the discharge wires on our yellow XT90 connector. You’ll need to strip back about an inch or so (2.5 cm) from the insulation on the red positive wire and tin the wire with solder. I find that a set of helping hands makes this much easier.
Next you’ll simply solder that red discharge wire onto the pre-tinned spots on your last module’s positive terminal. In this battery, that’s the 5+ terminal. Again, helping hands comes in pretty handy here. (Get it? Sorry…)
Continue the same way with the black discharge wire. Strip it, tin it, thens older it onto the -1 terminal of your battery. No matter how many modules you have in series, the black discharge wire always goes on the -1 terminal.
Once you’ve finished with the discharge wires, we can move on to the balance wires. I like to start by simply taping the entire balance wire bundle to the side of the pack, that way I can keep it nice and organized. You can use simple electrical tape, but I prefer kapton tape. It only costs about a buck more, but it’s stickier, easier to work with, non static and heat resistant. It simply works great for battery building and it’s what the professionals use.
Start with the red wire and solder it to the positive terminal of the highest numbered module you have, which is the 5+ terminal in this case. You can solder it directly onto the thick red discharge wire if that’s easier. Then simply work backwards, taking the wire next to the red wire and soldering it to the positive terminal of each successively lower module. If you’ve done it correctly then the second to last wire will go on the +1 terminal and the last wire will go on the -1 terminal.
Now is a good time to double check that you are getting the proper voltage at your discharge connector. These batteries are pretty hard to mess up, but if you aren’t getting the expected voltage, just double check your connections and make sure you soldered all the wires and nickel strip in the right places. Also, remember that you won’t get your full pack voltage yet because these cell modules are only partially charged. You should get the sum of however many modules you have in series.
Assuming everything checks out, go ahead and tape up all of your wires so they lay flush against your battery and won’t vibrate or work themselves loose over time. Again, I like to use kapton tape here but you can also use electrical tape.
Step 8: Sealing the battery
This is the last step: heat shrinking the battery. You’ll find two pieces of heat shrink in your kit, one should be a bit wider than the other. Start with the widest piece and slide it over the longest dimension of your battery. You want an overhang of about 1/2″ or 1.5cm on the sides. If you used straight packing like I did here, you’ll likely need to trim your heat shrink just a bit so you only have 1/2″ or 1.5cm of overlap on the sides. The heat shrink will come a bit wider to accommodate other layout styles.
Now use either a hair dryer on its highest setting or a heat gun on a lower setting to heat the shrink tube evenly. Hair dryers of 2,000W seem to work well, while lower powered ones may work, but can take longer.
I like to start on the two exposed ends and shrink those first to make sure they grab around the sides of the battery well, then I go back and heat the middle. Turn the battery around while heating to ensure that all parts of the heat shrink actually shrink down and squeeze the battery.
Next, take the second piece of shrink tube and slide it down over the entire battery. Again, make sure you’ve got about 1/2″ or 1.5 cm of overlap on each end. Now repeat the heat shrinking process and evenly heat the shrink tube, starting at the ends, until the entire shrink tube is wrapped around the battery.
If you wind up with any pieces on the ends that didn’t shrink down all the way and stick out like wrinkled folds, you use a pair of scissors to cut those back. Then reheat the spot to smooth the edge.
The final step is simply to add your sticker to the outside of the battery in order to show everyone that this is a Maker Battery and you built it yourself!
Congratulations, you’ve finished building your battery! Good luck with your project and have fun!