Let's Add an Active Balancer to the Electric Bike Battery

Hi guys, today we add an active balancer to the battery of our ebike so as not to risk some cells discharging and others not. Let's start immediately by unboxing the balancer.

I have also posted this project in PCBWay community, here is the link

• Active balancer for lithium batteries (3V - 4.2V)
• Battery pack at least 2S (two or more cells in series)

The balancer I bought is capable of balancing a 10s battery pack so with 10 cells in series (I leave it to you in the description anyway)

As soon as it arrives, probably from China, you will find it in an antistatic bag which is great for protecting components from electrostatic discharges that can be created in transport or in other situations.

The board looks very good in appearance, it is certainly of excellent workmanship and is covered by a layer of insulating liquid (I don't know exactly what it is).

This feature, in addition to the fact that the bottom does not have any type of solder, makes the board perfect to be placed directly on top of the cells in a battery pack without worrying that a pin soldered could ruin the insulation of the cells.

In addition, of course, the 10s connector also arrives in the box which is the same that you find in the BMS of the battery pack and this too, being colored with different colors, makes it perfect for not getting confused in the welding phase to the battery pack.

As a first test, I wanted to test if the balancer could also work with battery packs that are smaller than 10s (as in this case). So, I tried to attach the negative of the balancer to the negative of the battery and then from there on each wire to the positive of the first cell, to the positive of the second cell and so on.

Unfortunately, however, it did not work and I started looking on the internet to see if what I wanted to do could be done but not seeing the balancer LEDs light up in an intelligent way, I thought it was best to leave it alone.

Realized that trying to make a device work improperly was not what, I went through the test on my 10s3p battery pack of my Fiido D4S electric bike (great electric bike).

To do this, I had to remove the battery pack from its plastic casing, being very careful that there were no metal parts on the table or any risk of short circuits.

After that, I had to disconnect the BMS connector on the battery pack which is probably the only connector you will find on the battery pack.

Once you have accessed the BMS pins, you just have to take the balancer wires and connect them with the same order as the BMS connector to it, so yes, I mean to insert the balancer connector wires into the female BMS connector.

If everything has been connected correctly you can finally connect the balancer connector (which at this moment is nothing more than an extension of the BMS connector) to the balancer and you should see the balancer LEDs light up to indicate that balancing has started.

If the cells are perfectly balanced and nothing is moving on the balancer, simply take a 5ohm resistor (so it flows, when the cell is charged just one Ampere) and discharge a cell for testing.

Once you've tested the balancer, it's time to take the scissors and cut the battery insulation to reveal the cell heads to solder on.

For me the battery pack was covered with plain tape so it was pretty easy to remove everything.

Once you have gone through the scissors and pulled the tape from the wires or cell heads, make sure with a multimeter that the BMS connector wires are all still connected.

Before starting to solder the balancer wires, always first make sure that the connector wires are long enough to reach the end of the battery pack (and trust me, do it because there is nothing worse than redo everything because they were too short. wires)

But now it's time to move on to the hard part, solder all the balancer wires. To do this you will need nothing more than tin to solder and a soldering iron but above all you will need haste.

Exactly! Cells are very sensitive to high temperatures and it is not good for them to be subjected to heat for a long period of time.

Then with the BMS wires as a reference, solder the balancer wires to the exact same spots in the same order.

Once I connected the balancer to the battery pack, I discharged three cells together by connecting a 9V electromagnet with one pin to a random pin of the BMS connector and the other pin to another three pin pin away from the first pin on the BMS connector. .

After a while I was able to see the balancer signaling me, with the LED on the board, that the balancing has started.

Yes this is the moment when I realize that, after having connected and done everything, the balancer does not fit in the box.

But no problem, a maker must know how to arrange and for this reason, I decided to 3D print an extension for the box to allow the balancer to enter in a straight position.

To do this, however, I had to stretch all the threads so in order:

I had to unsolder the old xt60 connector therefore positive and negative power and then I unsoldered the charging connector which are two more wires.

I recommend, when unsoldering any wire, temporarily cover it with paper tape or electrical tape and never unsolder two wires at the same time and then isolate them: disconnect, insulate and move on to the next wire.

At this point I removed the battery pack from the casing again and I inserted the 3D printed extension and then inserted the charging connector into the cap and I widened the holes that were too small.

Once this was done, I soldered two red and black wires of the right section to the xt60 connector again and I insulated everything with heat-resistant sheaths which, however, I had to widen with a screwdriver.

After that, I ran the new red and black wires inside the cap and soldered them to the old silicone wires coming out of the BMS.

Then I close the cap, fix the extension with some cloth tape and ...

Oh yes guys, I took the bike, I opened it, I inserted the battery and it didn't go in ... or rather, it went in but with so much effort that to get it out I had to pull the red and black wires.

However, I repositioned the wires better so that they did not put pressure on the walls of the box and then it went in perfectly.

After this fight between me and a stupid battery, I finally managed to add a balancer that will keep me all the series cells of the battery pack well balanced so that I can make the most of the battery capacity and above all that it can keep it healthy. Thanks for reading the article, see you next time!