DIY Parallel Charger and Balance Board


24 Sep
24Sep

In this tutorial, we will be making a parallel charger for your LiPo batteries. Parallel charging is a fast and efficient way of charging multiple batteries at once. This way, you can get back in the air faster to fly! By making a charger, you will understand the concept behind it, and will be able to effectively use commercial parallel charger boards. Also, making a parallel charging system is much cheaper than purchasing a parallel charger board. However, there are a few things to know before you start.


Parallel Charger - Final-assembly

Background

Parallel charging is the process of combining multiple batteries into one larger battery for charging. For example, if I have five 450mah 2s LiPos, then by wiring them in parallel to make one battery, I would effectively be charging a 2,250mah 2s LiPo with one charger.

This means that if I wanted to charge at 1C, then I would set my current to 2.25 A, instead of 0.45 A for each individual 450mah 2s LiPo.

The wiring is really quite simple though. Simply said, it essentially involves connecting all of the positive wires from your LiPos into one wire, and all of the negative wires from your LiPos into another wire. Those two wires make up the larger battery ready to be charged.

The balance leads are done the exact same way. By connecting all corresponding leads to each other and wiring them to one balance plug, it is possible to balance charge your batteries in parallel also.

Only batteries of the same voltage and capacity should be charged together! This is an important safety measure to take note of.

Here is a general idea of how things are wired up:

Parallel-Charger-Schematic-Revamp

Building the Parallel Charger

I will be covering the two main parts of this DIY charger. The first part is the main plug harness. This is the part where you would plug in all of your LiPo’s main leads into. The second part is the balance plug board. You do not need to make this, but it will be safer to balance charge your LiPos instead of charging them straight up because the charger will be able to monitor each cell’s voltage. Of course, if you are using a 1s LiPo, then only the main harness is needed.

Main Harness

First off, you will need wire. Lots of wire. Make sure that your wire diameter (AWG size) corresponds with your battery type. For example, I am using 16AWG wire for an XT-30 harness. This should give me enough wire diameter to safely charge without the worry of the wires overheating or reducing current flow.

Start off by soldering your main connector to two long wires about six inches in length. This is the part that will plug into the battery charger. Next, cut ten pieces of wire around 2-3 inches in length. This will be enough to enable you to charge 5 batteries at once. Of course, you could add more, but the soldering can get a bit hairy, as the next step involves soldering them all together.


Parallel Charger - Small-cut-wires


This next step will be a bit more difficult. Solder five of your ten shorter wires together. Then, when those 5 are joined, solder one of the main wires from the main connector to the 5 leads. Depending on what wire you soldered them to, those will be either the positive side, or the negative side based on your connector. Make sure to take note of which side is which for the next step. Repeat the solder job for the other main wire.


Parallel Charger - Small-wires-soldered-to-main-wire
Parallel Charger - Battery-side-XT-30-soldered-to-harness


Now, solder each of your male battery leads to each of the shorter wires. These are the ports where you would plug in each of your LiPos. Make sure polarity is correct, or you could destroy a LiPo if the polarity is wrong! By doing this, the batteries will be wired in parallel to each other. You will not need to use all 5 inputs, as the batteries are not wired in series.

Now that you are finished, you can start parallel charging! Before you do though, remember to insulate all connections. This is a very important safety measure to follow, and is easy to do. Simply wrap exposed connections in electrical tape, or heat shrink if you have some.

If you want to balance charge also, then the next section will guide you through making your own balance charger board.

Parallel Charger - XT-30-insulated

Balance Board

The balance board will involve good deal amount of soldering, so make sure you have plenty of solder on hand. You will need a perf board, some male headers, and a 4s LiPo balance plug.

Parallel Charger - Perf-board-new
Parallel Charger - Header-x30

Start off by cutting each of the male headers into rows of 5. This is the number of wires in a 4s balance plug. One for ground, and four for each cell. Of course, you could add more by simply giving each header more pins. For example, a 6s LiPo balance plug would have seven pins, including ground.

As you can see below, my row of 30 pins was cut into 6 headers of five pins. This would let me balance charge six LiPos.

Parallel Charger - Cut-headers-x6

First, solder each header to the perf board. Try to get them evenly spaced out. Start off by soldering one to the end and then work your way down the board in a parallel manner. While soldering, it is important that there is proper heat transfer from the soldering iron to the joint. When the solder has completely filled and flowed around the perf board pad and has covered the pin sticking up under the board, then gently remove your iron. Do a quick visual inspection to make sure that the joint is shiny and does not spill into any other joints. The last thing you want is to have a cold solder joint. Remember that for joints like these, more is less in terms of solder usage. Just a tiny bit is needed for each pad.

Parallel Charger - Balance-plug-solder-joint

Once all of the headers are finished, create one long solder bridge going down the row. Start by tinning each pad with a small amount of solder. To do this, simply hold your hot iron on a hole, and apply a small amount of solder to the empty pad, just as if you were to solder a header pin in. The solder should then flow all around the hole and pad to create a nice disc of solder over the pad.

Then, going down the line, carefully bridge each solder pad to each other, letting the previous section cool before attempting to bridge the next connection. It may take some time to get this down, and I found that if I let the solder joints cool completely before attempting another bridge, it makes soldering faster and easier.

Parallel Charger - Balance-board-soldered

That being done, it’s time for the final solder joints! Pick one side for your ground side, and then solder your balance plug to each row of solder strips. Remember to insulate all exposed solder joints and connections. We DO NOT want a short anywhere to ensure safety. The parallel charging balance board is finished! Now all that’s left is to charge your batteries!

Parallel Charger - Balance-plug-soldered
Parallel Charger - Insulated-balance-board
Parallel Charger - Finished-balance-board

Using the Parallel Charger

The best way to use this DIY parallel charger is to incorporate both the main harness and balance board. While charging, the balance board will make sure that all cells are charging correctly, and the main harness will do most of the charging. Use only batteries of the same voltage and capacity.

Parallel Charger - Plugged-in-lipos-main-harness
Parallel Charger - Plugged-in-lipos-balance

When setting voltage and current settings in your charger, it is imperative to set the correct amount of cells and capacity. The number of cells is the same as all of the other batteries. The current however, is the sum of all the capacities of each battery, if you are charging at 1C. Charging at 2C would just be the sum of the capacities multiplied by two and so on. The formula for calculating charge current is: (1C*X battery capacity in A), so a 1500mah 4S LiPo would charge at 1.5A at 1C.

In your charger’s settings, make sure to enable the “balance” charge mode in order to ensure the monitoring of the cells. In my Imax B6, I just select “LiPo Balance” and then hold down the enter button twice.


This article was submitted through the FPV Community. by Lawrence Ro.

Views and advice in this article are that of the author and does not necessarily reflect the opinion or views of ATFPV