Simple 3.7V battery level indicator

Lithium-ion batteries with a voltage of 3.7 V are not used anywhere now. Do-it-yourselfers especially often use them wherever possible. Such batteries are good for everyone, but they have a number of disadvantages, one of which is that if the battery is discharged below the minimum value, then its service life is reduced exponentially. And in order to avoid this, and always monitor its charge level, I propose to assemble the simplest indicator on a single transistor, which will always tell you what state the battery is in.

You will need:

The BC547 transistor is common, finding it is not a problem.
The IN4007 diode is also not in short supply.
Two 220 Ohm resistors.
1 kOhm resistor.
Two 3V LEDs, red and green.

Assembling a level indicator for a 3.7 V battery

We fix the transistor and bend the collector and emitter to the sides.

Solder a 220 Ohm resistor between the base and emitter. And there is a 1 kOhm resistor to the collector.

To the 1 kOhm resistor we add a 220 Ohm resistor in series. Such a circuit is needed in order to accurately select the total resistance.

Solder the diode.

Now red Light-emitting diode.

And then green.

Solder the power wires.

Tests

The indicator has a threshold value of around 3.3 V. This means that if the voltage is below this value, it lights up red, and if it’s above it, it lights up green.

A very convenient “baby” that can be embedded anywhere and always know about the battery status.

A chain of two series-connected resistors can be used to adjust the threshold value of the state switching.

Watch the video

come back

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Comments (9)

#1 Guest Vasily Guests 21 February 2020 13:07
4

Where is the diagram???
- Answer
1. #2 Guest Vladimir Guests 21 February 2020 23:00
  3
  
  What the hell with the circuit, based on what you see, for example, the pinout of all foreign diodes is exactly the same, where the strip is there and the cathode, and there should be a minus on the cathode, and guess what on the anode, the terminals of the bc547 transistor are also clearly guessed, the base is in the middle, and since the transistor is n-p-n, its collector goes to positive, etc.
  
  Answer
  1. #3 Guest Vasily Guests 23 February 2020 05:29
    9
    
    I'm used to order. I've been working with diagrams all my life.
    
    Answer
#4 Ivan Guests 21 February 2020 16:35
3

The diagram on the video screensaver and in the pictures differs in the connection point of the positive contact. A fully charged lithium battery corresponds to 4.2V rather than 3.7V. Although the diagram can be easily reproduced from the picture, it would be better if it was given and nothing else is needed.
- Answer
#5 Mip Guests 12 December 2020 09:43
6

But what is more dangerous is a voltage rise above 4.5V and the indicator will not show this.
- Answer
#6 Guest SANYA Guests June 4, 2021 02:17
1

now why laugh. someone said, it’s more dangerous to go above 4.5 volts. the indicator will not show) but if you put together a couple of indicators) suddenly it is possible for it to show... one light bulb is 3 volts, the second is 3.5 volts, the third is 4 volts) something like this.
- Answer
1. #7 Yuri_ Visitors June 5, 2021 00:22
  1
  
  How about a bunch of indicators? one at 3, the second 3.5, the third 4 volts
  This site is full of simple level indicator circuits with several LEDs.
  and what would turn off at 4 volts
  From any dead lithium cell phone battery, you can pull out a tiny cell phone battery for free that does just that - turns off the battery when the voltage on it gets too high or too low.
  
  Answer
#8 Guest SANYA Guests June 4, 2021 02:19
0

How about a bunch of indicators? one at 3, the second 3.5, the third 4 volts, and what would turn off at 4 volts)
- Answer
#9 Vlad Guests November 30, 2022 11:42
3

“We solder a 220 Ohm resistor between the base and the emitter. And a 1 kOhm resistor to the collector.” This is exactly the case (why do you need a circuit), look at the pictures. It looks like it is soldered incorrectly in the picture. Quite the opposite. ;)
- Answer