how to balance nimh batteries

How to Balance NiMH Batteries? – 5 Methods

When you charge and discharge batteries, the voltage difference between the two terminals changes. This is why a battery’s terminal voltage needs to be monitored throughout its cycle.

That’s why you need to know how to balance NiMH batteries?

Well, there is more than one method to balance NiMH batteries. You can give both the batteries a full charge. Or you can discharge one battery. You can do it in several methods too. One way is to connect it to a third battery with more power in series. You can also connect one end of the battery to the ground.

That’s not all. There’s a lot more to know about balancing those batteries. We’ve mentioned 5 easy methods for you.

So what are you waiting for? Let’s start!

5 Ways to Balance NiMH Batteries

Balancing NiMH batteries are more technical unlike balancing RC tires. But don’t worry. Here are 5 methods to Balance NiMH batteries-

Method 1: By giving Them Full Charge

NiMH batteries can be charged at any time. But during charging, it has to be in a steady trickle that won’t produce heat. 

NiMH Batteries

The NiMH battery charger needs to have the same volts and amps as your battery. It’s to avoid damaging it in the process. It’s also worth noting that you need a specific charger for each particular battery. So make sure you get their compatible charger too.

You can use the NiMH float charge. Where the battery voltage is maintained at around 2.25 volts per cell.

Charging NiMH batteries is pretty easy in theory. But knowing how is what makes all the difference.

Method 2: By Maintaining Voltage on Both Terminals

First, charge the equipped battery to full capacity. Then remove it from the charger or power supply. Then connect the black lead of your Digital Multimeter’s red Test Lead to COM+. And the black lead of your Digital Multimeter’s red Test Leads to ground. Connect the negative terminal if you’re using a voltmeter.

Next, connect the red lead of your Digital Multimeter’s multimeter to the +battery terminal. And then connect its red test lead directly to COM+. Without touching anything else on the circuit.

You can use either a Mulitmeter or a voltmeter. Or, you can use a multimeter that has a voltmeter in it already. Like the AstroAI Multimeter 2000. You can check latest price on amazon

Allow NiMH charging voltage/current values for a couple of seconds before measuring them again. Using these values, calculate the new equilibrium on each side (CE).

Now that testing of  the RC batteries is done, let’s move on to the next part

Method 3: By Maintaining Voltage on One Terminal and Discharging the Other

Your batteries may lose charge because of the lack of a proper way to store the batteries.

Hold the soldering iron to one terminal of the NiMH cells. Do this until they both read 3 volts or above. 

Remove your solder wire from the terminals as soon as they display 3 volts or more. If you don’t have a soldering iron at home, you can check out Plusivo Soldering Kit. It comes with a lot of accessories. You can check latest price on amazon.

Take off the solder wire and set it aside. But don’t let go of the black wire. 

Insert one anode of your 1N4004 diode into one of the terminals. And attach the other end to the black wire that you’ve been holding on to. 

Now insert one cathode in another terminal. And connect the other end of this diode to your soldering wire (from earlier). 

Insert both of your AA battery holder’s wires from its terminals into the 1 Wireless Timer Switch. Connect one terminal to where you just inserted your Red (anode) Diode. And connect the other side to where you just inserted your Black (cathode) Diode.

Method 4: By Discharging One Terminal to Ground

This can be done using a multimeter or voltmeter. 

On your multimeter, connect each lead of an ohmmeter to one terminal of your discharged battery. Then remove the other terminal from the battery pack. And touch its end to one of the meter leads.

Make sure you read the voltage accurately. As you will compare it with another measured reading later on.

In this method, you measure both batteries at the same time. Because you are doing a discharge test of both batteries together. 

As you proceed, be sure that both packs are discharged to a low voltage. Instead of just one pack with a dead cell.

Method 5: By Assembling Them in Series or Parallel

The two most important parts of a NiMH battery are the positive and negative terminals. Each terminal is actually a separate cell connected together by lead-acid plates inside each cell. 

The problem happens when these plates connect with each other for one charge cycle. One of the cells will gain a full charge. While the other will lose all its capacity.

In a series connection, all the cells connect in the same line. The cell with more energy will be at the top. And will take all its energy to the other cell.

So use a third high-energy cell with the cell you have more energy in series with. Keep the volts measured with a voltmeter or multimeter. Then when it matches your cell that has lower energy, disconnect it. 

You’ll have your cell balanced. 

You can also use a charger to drain current from one battery. And then feeding on another battery.

You can also use a multi-cell charger for better balance. It can be called a NiMH charging circuit.  Like the SKYRC iMAX B6  Balance Charger Discharger. It’s a balancing charger for NiMh batteries. You can find it on amazon.

With this, you may have an “even” or “uneven” load.  You might also learn about connecting esc to brushless motor.

Frequently Asked Questions (FAQs)

How can NiMH batteries be refreshed?

Sometimes NiMH batteries need two or three shocks to be refreshed. If the voltage remains constant after three attempts, the battery must be changed. After the shock, the voltage should only increase to 1.2 volts per cell.

Do parallel-connected batteries self-balance?

Since parallel cells are physically related to one another, they will automatically balance. However, there needs to be a balance between the cell groups in parallel wired groups. That is wired in series.

What is the time required to balance a battery?

A NiMH with a 1A balancing current needs approximately a week to balance a 100Ah pack. During the charging period from 3.50V to 3.65V, do not leave the battery cell.

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