How to make a 4,8V TTL battery tester

Tomeu Simo, send us this 4.8v Battery Tester (TTL). Many thanks.

Electric scheme:

battery tester electrical diagram

  • One 55 × 40mm perforated printed circuit board
  • Integrated circuit LM3914
  • 2.2μF electrolytic capacitor
  • Diode 1N4001
  • Potentiometers (470Ω, 100Ω)
  • Resistors (10K, 20K, 2Ω 280, 100Ω, 825Ω)
  • 10 LEDs (4 red, 2 yellow, 4 green)
  • A box to put the whole set and hold the LEDs

See attached schematic for exact components.

Mounting the components on the board:

  • The resistors are mounted, then the two potentiometers, the electrolytic capacitor, then the diode and finally the integrated one

LED detail:

led battery tester

Components on board

battery tester components

  • The potentiometer R4 adjusts the intensity threshold that reaches the LEDs.
  • The R6 potentiometer is in charge of calibrating the tester.

Complete battery tester assembly

battery tester

3.-Calibration of the tester:

Take a 4.8v battery pack with the multimeter and check the voltage at the battery terminals. According to this voltage, look at the attached table for the number of the led that should be on. The battery is then connected to the tester, being careful with the polarity. With potentiometer R6 we will adjust until the illuminated led is the one we looked at before in the table and that corresponds to the current battery voltage. Next we put the table for the calibration.
4.51v - 4.60v # 1
4.61v - 4.70v # 2
4.71v - 480v # 3
4.81v - 4.90v # 4
4.91v - 5.00v # 5
5.01v - 5.10v # 6
5.11v - 5.20v # 7
5.21v - 5.30v # 8
5.31v - 5.40v # 9
5.41v - up # 10
This table is useful to know what voltage we have depending on the LED that turns on. With knowing which is the limit that we want for our batteries, then it will be enough that it is in a higher led and we will know how much charge it has left.

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