18650 battery level indicator

ffjbg June 23, 2024 ,Electrical

Are you looking for a simple circuit to measure your Lithium Ion single cell charging and discharging level? Here is one chip circuit, powered up from the same Lithium Ion battery you want to measure.

This circuit is designed to measure 3.7V rechargeable batteries level.

4.2V - 100%; 4V - 80%; 3.8V - 60%; 3.6V - 40%; 3.4V - 20%

LED1 - RED; LED2 - YELLOW; LED3 - YELLOW; LED4 - GREEN; LED5 - GREEN

D1 is used to protect a circuit from the battery being placed wrong way. You can use 1N4007 or something similar.

When this circuit was simulated on LTSpice, I used R1 value 18k, however, after this circuit was soldered on a printBoard, this value was to high, so I had to change it to 15k. It might be because of inaccuracy of the other resistor values.

Today I am going to make a circuit of 3.7V Battery low and full charge indicator.

Firstly we have to connect 1K resistor to Base and emmiter pin of the transistor as solder in the picture.

Now our circuit is completed and now we have to check this circuit.

Connect +ve of 3V battery to +ve leg of green LED and -ve of 3V battery to emmiter pin of the transistor as you can see in the picture.

~ As in abouve picture glowing Green LED Because this battery is fully charged.

When I connected 3V battery then Red LED is glowing and Green LED is also glowing in small amount.

~ Hence when Battery will be full charge i.e. 3.7V then Green LED will glow only and when battery will be low i.e. 1.5V then Red LED will glow only.