# Simple NiMH NiCd Battery Charger circuit

If you need an automatic nimh battery charger circuit that automatic cuts off. The circuit uses IC-AN4558 or LM1458 OP-AMP, to detect a battery voltage. And, it will cut off fast the battery when the power is full. It is a simple project, and low cost to save your budget.

How does it work?
We are reviewing and understanding a ni-cad battery. Someone may not know it. They have body same a general battery. But they are different. When the battery runs out. We can rechargeable into them again.

Figure 1 NIMH NICD Battery Charger circuit with automatic cuts off

And incidentally, the general battery of 1.5 VDC per one unit.
but the nicad battery that has just voltage of 1.2 VDC only.

In the circuit diagram, as Figure 1 this circuit, we use a DC power supply 6 volts to 9 VDC. Secondly, they are applied to input point diode-D1 and capacitor-C1, which is filtered current to smooth up.

Then, IC1 is an OP-Amp is connected to a voltage comparator circuit.

When we apply the battery to charging. During the first, the voltage across both battery less than 2.5 VDC, Which a positive will connects with pin 2 of IC1 so cause the voltage at pin 2 less than pin 3 of IC1. The voltage at pin 3 of IC1 will be adjusted at 2.6-2.8 VDC by a potentiometer-VR1. The output voltage at pin 1 of IC1 will have voltage is positive, LED2 glow and transistor -Q1 on can conduct current to the battery.

While the battery is charged, LED1 will do not grow. The circuit will still this states until the fully charged.

When the battery is charged fully then the voltage at pin 2 of IC1 will have value more than the voltage at pin 3 of IC1, the output voltage at pin 1 will be 0 VDC cause LED2 go out, but LED1 will glow instead. The transistor-Q1 will stop working because current that bias transistor-Q1 will flow through D2. This project will stop working.

On this automatic NiMH battery charger circuit,we can select current charging are 15 mA and 50 mA by selector switch S2.

How to build them.

In Figure 2 is an actual-size of Single-sided Copper PCB layout.

Figure 2 is the copper PCB layout.

Then assemble all components on PCB as Figure 3, to begin with lowest parts before example for resistors, Zener diode, socket IC, next to a tall parts example capacitors, transistor, LED etc.

Figure 3 is the components layout and wiring.

Remember we should look at the correct polarity parts, because this circuit may not works well such as electrolytic capacitors, LED, Diode, Zener etc.

The setting and application.
After that, we assemble all parts successfully. Then we adjust the voltage at pin 3 of IC1 by variable resistor-VR1. Which we use digital volt meter measure by positive lead at pin 3 of IC1 and negative lead to ground. We need to have voltage about 2.6-2.8 VDC which more than the voltage of nicad battery 1.2V + 1.2V = 2.4V.

The application is easy just we take DC adapter at more current than 300 mA up. And the voltage of 6-9 VDC to the input source. .we can select current 2 level is 15 mA and 50 mA. By it is set with resistors R1 and R2 and use switch S2 is a selector.

Calculate the time it takes to charge it with the formula.
Time (hour) = The capacity of the battery (mA) / The charging currents (mA)

If select current 50 mA will charge the nicad battery AA size which has a capacity of 500 mA, we need to take charge equal to 10 hr. But actually, we do not have to worry about it. When fully Charger will stop charging automatically. And LED1 indicates that the battery is fully charged will light up to us as well.

The component list

Resistors ¼ W +5%
R1—30Ω
R2, R6—100Ω
R3—1.5K
R4—10K
R5—2.2K

Variable resistors
VR1—10K

Diode
D1, D2—1N4001

Transistor
Q1—2SC1815

Electrolytic capacitors
C1—330μF 16V
C2—1μF 16V

Zener diode.
ZD1, ZD2—1N4731A___4.3V 0.5W
LED
LED1— Red
LED2—Green
Switch
S1, S2—SPDT- (Single-pole, Double-throw) switch.

IC1—AN4558 or LM1458
And others.

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luis barbosa

buenas tardes yo quisiera que me ayudaran
como poder hacer un convertidor de corriente
que se alimente de 6v o 9v y salga 32v 2ah
si me pudieran ayudar se lo estare eternamente agradecido sin mas quedo de usted

jose luis barbosa ortiz

John

It is a very interesting design. I gonna try it out. Thank you for sharing!

Helmut Ennikl

Hallo,
ich meine die Diode D1 in der Schaltung ist falsch gepolt.Positive Spannung kann nicht zu Q1-Ladetransistor gelangen.
Habe ich recht?

Viele Grüße
Helmut

Jbg

To Helmut: all Diodes are correctly connected. (Alle Dioden sind richtig eingezeichnet!)

Dejan

Hi nice circuit I need this charger for 7.4 Battery the original charger has 8.4 Volt output so how to change the circuit to work with 7.4 or 8.4 volt? Please I need help the charger is lost and was an Chinese brand also the battery but the battery is ok. Thanks.

IBN

Sir, pls I need a low cost automatic charger circuit for 4nos nimh battery 1.2v AA rated at 2600ma

Alex

Hi, thanks for share this circuit, it’s interesting. I built the circuit but I have 4,7v at the exit to the batteries, it’s not much?, it should not be 2,4v?, thanks…

Andrew Howard

Thankyou for sharing, very helpful. I have just one question, what happens if the batteries remain connected to the charger and too a load as well and they begin to discharge again, will the circuit start charging again by itself?. If so what voltage and if not how can it be modified so that it will and how do you adjust that threshold voltage?

“””It was really insightful.
Thanks for the info.
Wanna have more contents from you.
Cheers””””

Ajitkumar

Sir,
I have NI-MH 1.2 volt 2100mah 12 batteries pack. what changes should made this circuit or any other circuit has provided ?

regards

michael foster

Simple NiMH NiCd Battery Charger circuit
Parts list shows R5 as 22K Circuit Diagram shows as 2.2k
which value is correct.
Thank you.

remmy

Your Comment Here…can it be used to charge liion battery