# NiCd Battery Charger Circuit: How to Use Them for Simple Projects

Published on January 5, 2022 , Last modified on July 30, 2024
by Hommer Zhao

Are you looking for batteries for your project that can charge easily and fast? Then, consider getting a Ni-Cd battery.

Also, the Ni-Cd battery packs are more tolerant and perform under harsh conditions. Further, the battery is more durable than lithium batteries or lead-acid batteries. And the device has high energy, like alkaline batteries.

But what if you don’t have a battery charger?

Well, you can use a simple NiCd battery charger circuit, which is usually beginner-friendly, cheap, and works perfectly.

So, this article will discuss simple projects that use the NiCd charger and more.

Let’s Proceed.

## Ni-Cd Battery Charger Circuit Projects

Here are a few Ni-Cd projects you can construct:

### Ni-Cd Charger Using a Single Op Amp

Typically, you can use this Ni-Cd circuit to charge standard AA size NiCad batteries. But if you plan to charge NiCad capacity cells, it’s ideal to opt for a special charger.

And that’s because NiCad cells have a meager internal resistance.

So, even if you apply a slightly higher voltage, it will increase the charging current. Hence, this charger must include a circuit that will control the charge current to an ideal limit.

#### That said, the components you need for this project include the following:

• T1 – 9V
• FS1 – 100mA
• R1 – 8K2
• IC1 – CA314DE
• R2 – 10R
• D1 – 1N4001
• C1 – 470µF
• D2 – 1N4001
• D3 – 1N4148

We have a DC filtering circuit (C1), traditional step-down (T1), full-wave rectifier (D2), and isolation (D1). So, the other parts of this circuit help to regulate current.

#### How Does The Circuit Work?

The IC1 works like a comparator. It has a separate buffer stage, Q1, responsible for offering a suitably high output current functionality in this setup. Also, a 0.65V supplies the non-inverting input of the IC1. Plus, the D3 and R1 help to present the reference voltage.

Further, the inverting input connects to the ground via R2 inside the quiescent current levels. That way, the output voltage will be entirely positive.

Also, when you attach a NiCad cell across your output, a high current may attempt to go through the R2. This may result in the development of an equivalent amount of voltage across R2.

That said, it’s vital to note that you may have a slight voltage increase at this point. But it may reverse the IC1 input potentials when you have an increasing voltage. As a result, there will be a voltage drop at the output and around R2 to 0.65V.

So, the charge current your circuit receives and the output currents come from the current produced when your 0.65V goes across 10 Ohms.

#### Other Things to Note

If you want a proper charge current, increasing your R2 to 3 Ohms is crucial. After all, most AA NiCad cells have an optimum ideal current of about 45 or 50 mA. Hence, if you want to use rapid charger varieties with 150 mA, you must reduce the R2 value to 4.3 Ohms. That is, you should have 3.3 Ohms alongside 1 Ohm in series—if you can’t get the correct part.

While you’re at it, enhance your T1 to be a variant with a current rating of about 250 mA. Plus, it would help if you used a small bolt-on finned sink to install the Q1. Interestingly, your device should charge about four cells. But if you upgrade your T1 to a 12V, your device will charge up to six compartments. And you can connect the components in series over the output.

The components you need for this project include:

Capacitors:

• C1 – 1000µ/40V
• C2 – 470 p

Semiconductors:

• T2 – BD137
• D8, D9 – Green LED
• IC1 – 741
• T1 – BC547B
• D6, D7, D10 – DUS
• T3 – 2N3055

Resistors:

• R9 – 820 Ω
• R7 – 3.9 Ω
• R8 – 8 Ω
• R2, R3, R5 – 1K
• R12, R14 – 100K
• R6 – 15 Ω
• R1, R10, R11 – 10K
• R 4 – 100 Ω

• S1 – 3 position switch
• TR1 (capacity of transformer) = transformer 2 x 12V/0.5A

#### S2 – 2 position switch

The schematic of this setup is relatively straightforward. And you can develop a current source with this circuit using T3, T2, and T1. Also, the transistors provide a constant charging current.

But the only way you can activate the current source is by connecting the NiCad cells correctly. While you’re at it, ensure that you position your IC1 to check the network. And the component does that by confirming the voltage polarity across the output terminals.

So, if you rigged your cell appropriately, you’ll notice that the IC1’s pin two may not be able to change to positive as pin 3.

Consequently, your IC1 output will become positive. Then, the result will supply the transistor (T2) current base, base, base, which activates or turns on the current source. That said, you can use S1 in your setup to work as a current source limit.

Once you know the values of R6, R7, and R8, you can preset currents of 400 mA, 50 mA, & 180 mA. So, if you put your S1 at position 3, it means that your NiCad is in D cells. But at position 2, it means that the Ni-Cd cells are for the C cells. At point one shows that you can charge your NiCad cells.

#### Working Principle

The current source of this setup uses a fundamental principle. So, if you place your S1 at position 1, you’ll have a positive IC1 output. Then, T2 and T3 will initiate conduction by getting a base current. But you have to wire the circuit like a current feedback network.

Hence, the current through the transistors creates through the transistors produces a voltage around R6. Consequently, the current will trigger T1 to operate. If you have an increasing wind around R6, T1 can conduct more strength. Hence, you must reduce the base drive current for T3 and T2.

With this, your T2 will conduct less. And this results in a current increase in restrictions. Consequently, R3 and the NiCad cells will apply an excellent constant current. That said, when you connect some LEDs to the current source, it shows the NiCad charger’s operational status.

Once your connection is correct, IC1 will supply a positive voltage, and the NiCad cell will illuminate the LED D8. But, if you connect your cells with the wrong polarity, the IC1’s positive potential at pin two will be higher than pin 3. Consequently, the output of your op-amp comparator will be 0V.

When this happens, your current source will go off. Plus, your LED D8 won’t come on as well. Further, you may experience a similar issue when you don’t connect any cell for charging. It may occur because the increased voltage at pin two will be higher than at pin three because of the voltage drop across D10.

Further, you have to connect a cell with at least 1V to activate your charger.

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## FAQs

### How do you charge a NiCad battery?

You can use a battery power pack with two AA-size Ni-Cd cells. While you’re at it, charge your Ni-Cd device at 10% of its battery capacity every hour. And you can use a 120 mA current.

### Do NiCad batteries need a special charger?

The best approach is to avoid random battery manufacturers. Instead, charge your NiCad battery with a constant current. You can do this till the cell voltages level off or balance level. Also, avoid the lead-acid purposed chargers.

### Can you charge a Ni-Cad battery with a lithium charger?

Yes, you can. But you can’t use a NiCad battery charger for a lithium-ion battery.

### Can you use the same charger for NiCd and NiMH batteries?

No, you can’t. And it’s because both batteries have different battery charger controllers.

## Final Words

A simple NiCd battery charger circuit is quite resourceful—especially for Nickel-Cadmium batteries. But while you use it, ensure that you cut off the charging process when the battery power reaches a full charge. That way, you’ll significantly increase the device’s backup efficiency and boost the battery lifespan.