Here is a simple heater circuit that can be operated from a 12V battery. The first part of the circuit is an astable multivibrator build around the two transistors Q1 and Q2 .The ON time of transistor Q2 is set to 0.5 S. The ON time of transistor Q1 can be varied by using the POT R2.The output pulses at the collector of Q2 is used to drive the Darlington power transistor Q3(TIP122).The transistor Q3 drives the heating elements L1 to L3.The net heat produced can be varied by  selecting the desired combination of heating elements at the output circuit sing switches S1 and S2.The net heat can be also varied by varying the duty cycle of the triggering pulse using POT R2.

Circuit diagram with Parts list.



  • The circuit can be assembled on a general purpose PCB.
  • The transistor Q3 must be fitted with a heat sink.
  • The elements L1 to L3 can be 10W heating coils.
  • The switches S1 and S2 must be able to withstand at least 5A.
  • The circuit can be powered from a 12V battery.
  • The LED D1 gives a visual indication of the duty cycle of the circuit.


  1. Like this design very much! I can recommend this to our clients, by the way, what’s the capacity of the 12V battery?


    please provide the details of heating coil;is it available at market….?
    can we use soldering heating coil….?

  3. Masoud azmel

    Was a very nice circuit
    with this i and my freinds when nights come out home and Sit together use it and very pleasur.

  4. Sir can i use this on ac to dc converted supply ? and what output is required for that and also send me the Details of Item is required for that project. (capacitor & Resistor)

  5. pls does any type of amp for 12v work for this circuit pls

  6. pls what is the meaning of the 1.5m and 4.7m in this circuit because i dont know the meaning of the m

  7. Seetharaman, i have TIP41, can i also use it as replacements for TIP122

    • Seetharaman

      Hi Rex TIP41 is a NPN transistor with just 6Amps absolute maximum collector current and a current gain of just 30 to 70. You have to use this with 2N3055/BD182 as darlington, of-course TIP41 in the input side.

    • seetharaman

      The equivallents are MJ802, MJ3001, 2N6283, BDX54, BDX69, or simply a BD139 with BD182 or 2N3055 as discrete darlington can be used.

  8. sir
    very nice popular website……
    i am live your website..
    thanks sir


    I need a running LED circuit with speed control and how to expand the number of LED?Please send me.

  10. Is this heater is used for heating water…plz give reply

    • Emmanuel

      is this water heater?,can i increase battery voltage to make it more suitable larger home use? I am most grateful. Please do reaply.

      • Seetharaman

        This is not a water heater. this is a small constant temperature chamber for calibration of rtd thermisters etc.

  11. how can run and store microcontroller pic and ATMEGA16 AND ATMEGA33 AND HOW STORE DATA IN MC.
    HOW DESIGN USING MICROCONTROLLER(89C51) TO RUN (BLINKING) 100LEDS .Please sent program in my mail.

  12. Hi is this water heater which is discussed here
    Can i use 12 V adapter to power the Circuit. If i am using 12v adapter in circuit then whats the power consumed for 1 hour/day.

  13. Seetharaman

    Hi Kulwinder the battery should be connected between +12 and common ground.
    Hi Wash each heater has got a capacity of 10watts. a total of 30watts energy is available.

  14. Hey I’m building a project which involves a DC heater. I would like to find out how hot this call actually get. Thanks

  15. kulwinder singh

    huy guys i have read all the circuit but i am unable to understand that where battery ‘s output nodes

  16. thnk for your info… but i want a small battery like 12v..

  17. seetharaman

    Hi ABDS with a car battery of 40AH it will work for 12 to 24 hrs depends on the heating required.

  18. Dear writer
    Just wonder who many degrees C can it provide as a maximum

  19. I really appreciate your effor. \pls kindly send me details on how to design and build 1000watts inverter/ ups

  20. Is this heater is used for heating water?If so what will be the output temperature ?can we use this for space heating?What is the battery back up?

  21. Thanks very nice project but u didnt mention the current ratings of the battery to be used like 12v@10amp,12v@12ampsetc.moreover the output temperature is not mentioned

    • I tested the circuit using a 12V,7Ah battery from my motor cycle.

  22. tijani mutiu

    Thanks for the message , but i also need the circuit diagram of 50 watt amplifier with double input and output and all neccesary information about it. thanks and GOD bless you