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How to Make a 25 Amp, 1500 watts Heater Controller Circuit

How to Make a 25 Amp, 1500 watts Heater Controller Circuit

In this article we will try to understand the making of a 1500 watt simple heater controller circuit at 25 amp current rate using an ordinary triac based dimmer switch circuit

 Using Advanced Snubber less Triacs

Controlling heaters rated as high as 1500 watt requires stringent specifications with the controlling unit for safe and effective implementation of the intended operations. With the advent of advanced snubber-less Triacs and Diacs making heater controllers at massive watt levels has become relatively easier today.

Here we study a simple yet entirely suitable configuration which may be utilized for making a 1500 watts heater controller circuit.

Let's understand the given circuit diagram with the following points:

How the Triac/Diac AC Controller Works

The set up of the circuit is pretty standard as the the wiring is very similar to the ones which are normally employed in ordinary light dimmer switch circuits.

The standard triac and diac set up can be seen for implementing the basic switching of the triac.

The diac is a device which switches current across itself only after a certain specified potential difference is reached across it.

The following network resistors and capacitors associated with the diac are chosen such that they allow the diac to fire only as long as the sine curve remains below a certain voltage level.

As soon as the sine curve crosses the above specified voltage level, the diac stops conducting and the triac is switched OFF.

Since the load or the heater in this case is connected in series with the triac, the load also switches OFF and ON in accordance with the triac.

The above conduction of the triac only for a specified section of the input sine voltage curve, results in an output across the triac which has the AC chopped into smaller sections, making the overall RMS of the resultant drop to a lower value, depending upon the values of the relevant resistors and capacitors around the diac.

The pot which is shown in the figure is used for controlling the heater element which initiates the above explained procedure. The greater the resistance, the longer it takes or the capacitor to charge and discharge whih in turn prolongs the firing of the diac/triac pair.

This prolongation keeps the triac and the load switched OFF for a longer section of the AC sine curve which results correspondingly lower average voltage to the heater, and the heater temperature remains at the cooler side.

Conversely when the pot is adjusted toward to produce a lower resistance, the capacitor charge and discharge at a faster rate making the above cycle rapid which in turn keeps the average switching period of the triac at the higher side, resulting a higher average voltage to the heater. The heater now generates more heat due to the increased average voltage developed across it via the triac.

Circuit Diagram

Controlling through Arduino Pwm

The above simple 220V dimmer switch control can be also effectively implemented using an external Arduino PWM feed through the simple method shown below:


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

69 thoughts on “How to Make a 25 Amp, 1500 watts Heater Controller Circuit”

  1. Hi, will this work on a carbon filament in convection cooker, and I’m also planning to control via arduino at a later stage any tips?


    • Hi, yes it can be used for the mentioned heater.

      For Arduino control I have updated the design at the bottom of the article

  2. I purchased a Chinese voltage control module (MY12BAZC11000) hoping to make a 2 tube quartz radiant heater (1500W) more comfortable by adjusting for a comfortable glow of tubes rather then the on/off thermostat. My plan worked well until the triac got too hot and failed. I was thinking maybe the same module but providing a larger heatsink for the triac. What are your thoughts?

    • Hi, the 40uH and 0.1uf/400V is not crucial, you can eliminate it if you want, it is included to reduce RF interference in the atmosphere.

      But if you intend to make it, you can roughly design it by winding 200 turns of 0.5mm magnet wire over a small ferrite core

  3. Day. Do you maybe have a circuit for me to control the speed of a 2200 watt angle grinder using 220 Volt
    board needs to be small so i can fit it in the grinder handle if possible
    Shanks for everything you been teaching all of us.
    kind regards

  4. Hello sir, can i replace 470k pot with another lowest res pot? Kinda 100k. And how aboit another resistor? Should i replace it?
    Because i want to make a variable watt using slider potentiometer.

    • hello dektian, 100k will not do, because it will not allow full control of the heater, but you can try 220K instead…or you can use two 100K pot in series.

      no other resistors will need to be changed.

  5. Hi I am very interested in this circuit
    I wish to use it for a 5500 watt water heater. Would I be right in saying I would only have to upgrade the triac? And also what type heatsink would be appropriate? Thanks in advance

    • Hi, you can use the above circuit for your application, the same triac which is shown in the diagram can be used, or a BTA41/600V can also be tried, but make sure it is mounted on a large heatsink…..and also the diac should be rated to handle at least 100mA

  6. sir i have done it but i am not able to adjest variable resistor(heatis not regulating), and my 40uh is heating.what i should do??

    • first test it using a 200 watt bulb to ensure that everything is correctly done in your circuit…after that you can use the heater coil…make sure the triac is mounted on a heatsink

  7. Sorry I wasn't that clear. Let me try this again. I'm asking for your help because your circuit here is close to what I would like.

    I have a forced air heater that is rated at 1500 watts, 6.3 amps that I would like to control, on/off, with a MCU. It doesn't need any thermostat functions, I'll handle that via code. I don't have much room where the wiring is located in the wall so something small would be nice. An added bonus would be to combine a power AD/DC circuit into this design. I already have power, just need to convert it to DC. I don't what to have to run a AC/DC adapter for power as I don't have an outlet near the area I'll be accessing the power/wires for the heater.

    I tried using a 25 amp SSR like this one http://www.ebay.com/bhp/ssr-25da but it failed. It got way too hot. I would rather not use a mechanical relay due to the clicking sound and the possible arcing of the relay. I also bought a 16 amp SSR but it gets too hot also. I read that the SSR should be twice the rating as the device it is controlling but I think I'm still missing something else to keep the circuit small and cool.

    If this still isn't clear I can try again or if I'm asking for too much help I understand.

    Thanks for your time and help.

    • From your explanation it appears that you intend to control the heater through some kind of predetermined algorithm through your MCU, that would periodically switch OFF and ON the heater and try to maintain the temp at the required level.

      In that case the above circuit may be completely irrelevant to your need.

      even the relay or the SSR won't be required.

      You just have to feed your MCU trigger to a MOCxxx based circuit and enjoy a smooth implementation of the system.

  8. Not sure if my other post went thru, but thanks. That link is a good start. I had a S216S02 and built the relay driver for it. It's working but I'm sure it isn't going to handle the 1500 watt heater, or will it? I'm not sure how to finish this so it can. I can't quite make out the parts needed for you circuit or how to get the relay driver to work with it either. Your help with this is appreciated.

    • yes I have answered your previous comment, I may be late but I normally never miss any.

      the relay is supposed to be at least 20amp rated, such as this one:


      the relay driver transistor should be a 2N2222 for handling this type of relay.

      actually you should have explained the entire sequence of the required operation, so far you have mentioned it in bits and parts…if possible tell me the whole sequence then probably I'll be able to help you in a better way.

  9. That's a perfect start, thanks. Now, how do I integrate the relay driver with this circuit to drive the 1500 watt heater? Also, if it's possible, can I add to this circuit the ability to supply 5v DC to power the MCU?

    Thanks for your time and help, I really appreciate it!

    • connect the relay pole to one of the AC inputs, it could be the phase or the neutral doesn't matter. connect the N/O contact with one of the input wires of the above circuit and let the other wire connect directly with the second mains supply input.

      this will control the ON/OFF switching of the above circuit but the actual heat control can be implemented only through the given 470K pot

  10. Swagatam, I'm hoping you can help me out with this type of circuit. I'm not an electronics expert so reading most circuit diagrams are just confusing, but I'm trying to learn.

    I would like to create this circuit but I need it to control a 1500 watt, 6.3 amp restive load heater via a MCU. I have to watch the heat and would like the circuit to be as small as can be. Can you help point me in the right direction? Maybe a circuit design a preschooler could figure out? 🙂 I would love it if I could also pull 5v dc for the MCU at the same time?

    What I'll have available at the mains wall is the line that completes the circuit. I would like to not have to rewire the the line to the heater for this circuit. Crude drawing below to help, hopefully.

    AC from wall –> to heater
    ++ = this would be the relay/power circuit to complete the circuit to turn on the heater.
    + = ground is tied straight thru to heater

    (common) ——- (++) ———
    AC Heater
    (ground) ———–+———-

    Thanks for the help,

    • I appreciate your interest John , however my knowledge regarding MCU programming is not great so it would be difficult for me to program the coeds for you, so I am sorry I won't be able to help you with this implementation.

    • Thanks for the response, What I'm after is just the relay/power circuit that would have a pin that I could connect to the MCU, so I would raise the pin high and it would trigger the relay. I'm good with coding the MCU just not with electronics so trying to figure out your circuit and modify it for my heat requirements and adding a pin for control on/off is beyond my skill set. This would be something like the link below but of course better and with the requirements above.


    • Thanks for the reply. I'm actually just looking for help with the circuit. I was hoping your design could be modified to have a pin that the MCU would connect to so it could trigger the relay on/off. I can code the MCU just can't design circuits.


    • In the above referred relay driver stage, the base of the transistor could be connected with the MCU trigger, for activating or deactivating the associated relay… this is what you were looking for, right?

  11. Sir, could you please tell me what changes are required in this circuit to make a heat controller circuit for about 500W-700W, 10-15A device powered from a DC source of 48V?

  12. Swagatam, Thank you for your prompt answer. One further question. Is this considered a "Constant Current" controller? I guess a typical thermostat control has a range when it switches on or off, a sort of fluctuation range? Is this a stable control when set? Sorry for the basic questions. Thank you.

    Kurt Kenyon

    • It can be considered as a constant voltage controller, and if the voltage is constant current will be also constant.

      so, a fairly good consistency can be expected using this circuit in terms of power output to the load.

  13. Swagatam, Can this setup be used with 110v and 1500 watt element? What would need to be changed? The element I was thinking of is for a hot water heater. Thanks so much.

    • Hi Kurt, yes it can be used with a 110V input, the 470k pot will need to be replaced with a 220k pot, that's all…rest can be as is

  14. Dear sir,
    I have eurotherm TS200A temperature controller.this is thyrister based. This required 0-5V control voltage. I want one temperature control circuit when temperature is 25deg C the voltage is 0V. Temperature reduces the control voltage increase from 0-5V. Please provide the circuit diagram.

    Thank you.

  15. Sir,
    I want to make it for 2000 W water heater/Gyger, before construction I want to make clear some points
    1. Resistances are used here — what are there wattage value
    2. Capacitor are used here are of micro farad or nano farad?
    3. How to arrange/make the inductor, if we omit this will circuit work ? what is the wattage value of inductor, if possible mention the range of inductor(from this value to this value) which will work,
    4. Both diac and triac needs heat sink

    • Akash,

      all the resistors can be 1/4 watt rated.

      capacitors are all uF (microFarads)

      Inductor may be built by winding around 100 turns of 1mm magnet wire over a 1cm diameter ferrite rod

      only the triac would need a heatsink, not the diac.

    • no diacs are never polarized but here it should be a heavy duty type not the usual small blue colored ones, the right one would look quite like a 1N5402 diode.

      try the circuit with the 200 watt lamp initially, once the dimming function is confirmed you can go ahead with the intended higher load

    • Thanks for reply
      Can only find small coloured diac
      Spec shows itrm=2A p=150mw
      could this be the problem?
      Any makers name part number etc

  16. Hi
    Tried your circuit and blown two triacs. Please confirm the connection of triac.
    You say the centre connection should go to the capacitors but the data sheet shows the centre is T2 which the diagram shows connected to 15K & choke. Tested using 40watt bulb as a load and each time it flickered few times and the triac failed.

    • I am sorry, it should be the left lead (A1) which must join with the capacitor common rail while the center lead goes up and joins with the 40uH choke.

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