How to Convert Fluorescent Starter to Thermal Switch





Introduction: How to Convert Fluorescent Starter to Thermal Switch

About: Electrical Engineer

Fluorescent starter is essentially two bimetallic strips in a sealed glass capsule, with a small gap between them.

The principle of this experiment is Metal expansion and contraction .

1-  12 volt CPU Fan.
2-  12 Volt supply.
3-   Fluorescent starter.
4- Candle.

1- Break the starter glass and try to not damage the metal inside (Take all safety precaution when you do that to avoid any injury).
2- Make sure that there is a small gap between two metal as shown in attached picture. 
3- Connect the circuit as attached in the first circuit diagram and fix the starter about 2 cm above the candle.

When the candle lighted up ,the starter metal  will expand and attached together , the fan will turn on  and turn off the candle ,the two metal will de-attach and turn off the fan.

Note that CPU fan is a brush less dc motor and it will not cause spark in starting ,the spark can damage the metal and it will not work for long time ,so if you connect a load that take more current  and cause a spark in the starter you can use transistor showed in the last diagram to avoid this issue .

if you find this tutorial useful to you , please vote for it in the Electronics Tips & Tricks contest.
Many thanks


Electronics Tips and Tricks

First Prize in the
Electronics Tips and Tricks



    • Casting Contest

      Casting Contest
    • Make it Move Contest

      Make it Move Contest
    • Oil Contest

      Oil Contest

    We have a be nice policy.
    Please be positive and constructive.




    it is very good and i made it for my school exhibition i got first thank you very much for this project

    1 reply

    should try it with a smaller fan? and or angle the fan so it doesnt blow the candle out?

    your rock Husham Samir!!!

    Love it! You made a "most useless machine in the world" (see vid and somewhere on this site...) while demonstrating a clever thermo-switch. Thumbs up!

    1 reply

    Nice video ,I love it ,thank you for sharing.

    very nice .................................but why did you use TRANSISTOR in this project ............?

    1 reply

    Thank you Divya
    if I am not using the transistor ,the circuit will work but a spark will happened every time the metal attached and it will damage the bimetallic strips ,so the purpose from the transistor to increase the life time of bimetallic strips.


    Good project, excellent thinking out of the box ! !


    1 reply

    Nice info. i think by modding the gap between the terminals, once can make a parked car cooler using a similar circuit. it will automatically start the fan and rotate the air inside the car when the temperature rises and shut off when cooled.

    can you do a test and measure the temperature when it starts bending? so we can accordingly know when it switches at what temperatures..


    1 reply

    Thank you francisdsa
    I have tried your suggestion but unfortunately it is not efficient because the two metal is too small and not easy to twist them to get the required setting .
    for a project like parked car cooler I suggest you to use LM35 temperature sensor with op-amp comparator .

    Very interesting, thanks for sharing.