This is NiMH battery charger circuit with auto cutoff.
A nickel-metal hydride battery, also known as NiMH, is a secondary cell. It is a type of rechargeable battery. They are used extensively, in cameras and other electronic devices.
Because it is cheap and very common for AA cell in many Capacity as required. We can replace the generic battery right away.
Important. We can a new recharging a lot of times depends on its capacity.
- Lower capacity, 1700 up to 2000mAh can be recharged up to 1000 times
- 2100 to 2400 mAh batteries can give between 600 to 800 times
- The greater power capacity, AA 2500 mAh rechargeable batteries can only be recharged approx 500 times
All rate in slow charge mode.
We will see that it saves a lot of money. But it needs a good battery charger. We can buy an instant one in a store near your house.
But we are electronics inventors. We should build it ourselves. Because it is cheap and of good quality.
The project is the NiMH battery charger circuit with automatic cutoff when fully charged. You can charge the batteries from 2-8 pcs, depending on an input voltage.
In the circuit has two LED indicators.
- First LED, show charging status, when the battery is full, it will be off.
- Second LED, connect the battery correctly.
The input voltage can use the power supply of 12V, 2A. At the charged current up to 800mA.
Note: This circuit is also automatic nicd battery charger circuit, too. For example Nicad battery 1500mAh, 1.2V. Now I never see under 500mAh.
How it works
Updated: 22 Jul 2019
Figure 1 Automatic NiMH battery charger circuit using TL072
The circuit in Figure 1, when we connect a battery to both points P3 and P4. LED2 will glow up, in case all battery connects correctly. If battery reverse polarity, this LED2 go out, we need to check them again.
Some voltage from the battery is compared to IC1. Which the TL072 is set in a voltage comparator circuit at between pin 2 and pin 3.
In case the voltage from the battery to charging each cell is still low. The output from pin 1 of IC1 will send to a transistor Q1.
The transistor-Q1 will switch on-off a working to transistor-Q2. So the current can flow to the battery.
While the circuit is charging, LED1 will show charging status.
When the battery is full, its the voltage is compared at the IC1 will make an output at pin 1 of IC1 go to stop working of Q1. Then also causes the Q2-transistor stop.
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The end of battery charging and LED1 is off, to display that the battery is full enough.
The amount of current in the charging battery of the project is determined at 800mA. By there is R7-resistor is a current limiter as above.
The S1-switch, to start charging, in the case that the battery correctly. We also press S1 to recharge again, to test that battery is fully or not.
Here is PCB layout by Lennie Zink. Thanks for your share and suggestions.
He is an excellent electronics hobbyist. I like his life. Read more: Lennie’s Projects
How to builds this project
This project has a few components so easy to build. First, make the single-sided PCB layout as Figure 2 or can also use easily the Universal PCB Board. Then assemble all parts on the PCB as Figure 3 We just recommend a short detail, because I think you can create easily yourself.
PCB layout of Automatic NiMH battery charger circuit
The Component layout for the PCB.
The Detail Components
IC1 = TL072—LOW NOISE J-FET DUAL OPERATIONAL AMPLIFIERS = 1 pcs.
Q1 = BC327—50V 800mA PNP Transistor = 1 pcs.
Q2 = MJE2955—50V 3A PNP Transistor = 1 pcs
D1,D4 = 1N4148—75V 150mA Diodes = 2 pcs.
D2,D3 = 1N4001—50V 1A Diodes = 2 pcs.
C1,C4 = 1000uF 25V—Electrolytic capacitors = 2 pcs.
C5 = 1uF 50V—Electrolytic capacitors = 1 pcs.
C2,C3 = 0.1uF 100V—Polyester capacitors = 2 pcs.
0.25W 1% Resistors
R1 = 10K = 1 pcs.
R2 = 1M = 1 pcs.
R3,R9 = 1K = 1 pcs.
R4 = 470 ohms = 1 pcs.
R5 = 150 ohms—2 watts = 1 pcs.
R6, R8 = 100K = 2 pcs.
R7 = 1 ohms-2 watts = 1 pcs.
Also these NiMH battery charger circuit
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