How To Do A BMS Reset For An Electric Battery.

As an e-bike owner, there may come a time when your battery will stop working. Common wisdom would tell you that you should try turning it off and then on again, just like when resetting any other electrical device that’s acting up. But how do you do that when you’re talking about the battery itself?

When it comes to a problematic e-bike battery, you’re not trying to reset the battery itself. Instead, you’re resetting the Battery Management System or BMS, the circuit board that controls the battery. You can do this external by briefly charging it through the discharge port. Or, you can do this internally by disconnecting the wire harness from the BMS itself.

In this article, we’re going to explore everything you need to know about doing a BMS reset for an e-bike battery. Keep reading, and you’ll learn two methods of resetting the BMS. Before that, however, we’ll cover the basics of what a BMS is and why you might need to reset it.

That’s important so that you know what you’re dealing with before attempting a BMS reset.

Let’s get started!

Recap: What Is A Battery Management System (BMS) And Why Does It Matter?

Before we get to the important stuff about performing a BMS reset, let’s make sure that we’re all on the same page about what a BMS is and what it does.

A Battery Management System (BMS) on an e-bike battery is a small circuit board inside the battery pack. It controls how the battery charges and discharges to ensure that everything stays within a safe range. 

In doing so, the BMS prevents overheating and helps lengthen the battery’s lifespan.

Why Would You Need To Perform A BMS Reset?

So, why would anyone need to perform a BMS reset? Well, if you’re reading this article, you’re probably here for one of two reasons.

Firstly, it could be that your battery isn’t working. To be exact, your e-bike battery isn’t charging or discharging as it usually does. In such a case, a BMS reset could be exactly what you needed.

The second possibility is that you’ve been troubleshooting a battery problem with the manufacturer’s Customer Service or a fellow e-bike enthusiast, and they’ve told you to try resetting the BMS.

In either case, they’re probably right. Performing a BMS reset could solve whatever battery problems you’re facing. Plus, it’s an excellent first step to troubleshoot the issue and potentially avoid buying an expensive replacement unit.

So, how do you perform a BMS reset?

Keep reading.

What Tools Do You Need To Reset A BMS?

The tools that you’ll need will depend on which method you use to reset a BMS. In this article, we’re going to look at only two approaches: resetting your BMS external and internally.

For resetting your BMS externally, you’ll need:

  • Safety gloves to keep your hands protected.
  • Wire cutters.
  • A soldering iron.
  • A standard multimeter.
  • A DC barrel jack receptacle.
  • A red wire and a black wire. 

However, if you prefer to reset the BMS internally, all you’ll need are:

  • A flathead screwdriver.
  • A plus or Phillips screwdriver.

Remember: Even though this article offers you two options for how to perform a BMS reset, you might still need to do both. One method might not work at first, forcing you to attempt the second method.

Whatever the case might be, it’s essential to start with the method that you feel most comfortable with. Suppose you’re unsure about working with things like soldering irons and wire cutters. In that case, it’s best to leave that to a qualified technician.

Step-by-step: How To Do A BMS Reset For An Ebike Battery

As mentioned before, there are generally two ways to reset the BMS: to do it externally or internally. You could choose to try whichever one you feel most comfortable with. However, if it doesn’t work, you may need to try the other approach as well.

Still, let’s take a closer look at both approaches.

Reset The BMS Externally

The first method for resetting your e-bike battery’s BMS is to do it externally. By that, we mean performing a reset without opening the battery compartment and accessing the BMS directly. To do that, you’ll be using a makeshift adapter to charge the battery through the discharge port, which should cause the BMS to reset itself.

Here’s how to make that adapter.

Step One: Create the Adapter

First of all, you should put on your safety gloves. You’ll be working with a soldering kit and later with live electricity, so you’ll want to keep yourself protected at all times.

Your adapter will consist of the DC barrel jack and two wires. Using the soldering kit, attach a red wire to the positive terminal of the jack and a black wire to the negative one.

You could also use electrical tape to keep it all together and cover any bare parts.

Step Two: Test the Adapter

Here, you’ll be plugging one end of the adapter into the battery charger. With your multimeter, check that the adapter is conducting electricity. Remember: red wire to positive, black wire to negative.

You must never let the bare wires touch each other, as that could close the circuit and make things very dangerous.

Step Three: Perform The BMS Reset

Next, connect the adapter to the battery’s discharge port. Look closely at the port, and you’ll see that it has indicators to show you where to plug each wire. It’s usually printed on the plastic itself. The red wire goes to the positive terminal, and the black wire goes to the negative one.

If it’s working, you’ll see that the light on the charger turns red. Hold the wires just as they are for 15 seconds, and that should cause the BMS to reset itself.

Once that’s done, turn off the battery charger and remove the adapter. You can now check to see if the BMS allows the battery to charge and discharge as normal. You can do this by replacing the battery back in the e-bike or connecting it to the charger.

Reset The BMS Internally

As you can see, resetting the BMS external involves working with live electricity, some custom wiring, and a DC adapter. If you feel unsure or uncomfortable with working that way, don’t worry! That’s totally normal. Many people would prefer using this second method instead, as it’s much more straightforward. 

Here’s how you can go about resetting the BMS internally.

Step One: Open The Battery

Firstly, you’ll need to use your screwdrivers to open the battery’s top cap. Typically, there are a few screws that keep the top cap in place. 

Doing that will give you access to the inside of the battery, where you will find the BMS, battery cells, and the wires that connect everything together.

Step Two: Pull The BMS Chip Out Slightly

The BMS and battery cells are kept safe deep inside the battery case. So, to make it easier to work on, you’ll want to gently slide everything out by just a little bit. You don’t have to remove everything entirely; the goal here is to have the BMS out in the open so you can inspect it closely.

Remember: Don’t pull forcefully on any of the wires or cells that you see. A gentle nudge is often all that’s necessary. 

Step Three: Reset the BMS

Take a closer look, and you’ll see that the BMS has several wires connecting to it in the form of a harness. Here’s what you’ll need to do next:

  1. Disconnect that wire harness.
  2. With the wire harness disconnected, plug the charger into the battery. Your charger should be on. 
  3. Lastly, reconnect the wire harness to the BMS and seal all of the parts back in the battery case just the same way as before.
  4. Then, test the battery to see if it’s working correctly again. Remember to check that the battery can both charge and discharge. Test its charging ability by plugging it into the charger, and test its ability to discharge by putting it back in the e-bike.

Final Thoughts

At this point, it’s safe to say that learning how to do a BMS reset is an essential skill for any e-bike owner. Having that ability would save you plenty of effort (and money) if you were to ever experience a battery that refuses to charge or discharge correctly.

Thankfully, there are two methods that you can choose from. The first involves resetting the BMS externally, which involves wiring up an adapter on your own and charging the battery through the discharge port. This approach can be quite challenging and risky for some people.

Alternatively, you could also perform an internal BMS reset by accessing the inside of the battery itself. This is a somewhat safer and more straightforward solution.

Whichever method you choose may not be effective, forcing you to try the other one as well. Still, if you’re ever unsure, it’s always a better option to take the battery to a qualified technician who can perform the reset and diagnose any problems for you.