Monday, October 28, 2013

Simple Induction Heater Circuit - Hot Plate Cooker Circuit

The proposed induction heater circuit exhibits the use of high frequency magnetic induction principles for generating substantial magnitude of heat over a small specified radius.


The discussed induction cooker circuit is truly simple and uses just a few active and passive ordinary components for the required actions.

According to the involved principle when a change in magnetic field is forced around a metal, electrons inside the metals get agitated and begins flowing across the metal, this is termed as eddy current. This flow of current in the metal or the introduced conductor causes a heat to be generated in the metal making it warmer.
The generated heat is proportional to (current)^2 x resistance of the metal.

The above heat is also directly proportional to the induced frequency and that's why ordinary iron stamped transformers are not used in high frequency switching applications, instead ferrite materials are used as cores.

However here the above drawback is exploited for acquiring heat from high frequency magnetic induction.

Referring to the proposed induction heater circuit below, we find the concept utilizing the ZVS or zero voltage switching technology for the required triggering of the mosfets. The technology ensures minimum heating of the devices making the operation very efficient and effective.
Further to add, the circuit being self resonant by nature automatically gets sets at the resonant frequency of the attached coil and capacitor quite identical to a tank circuit.

The circuit fundamentally makes use of a Royer oscillator which is marked by simplicity and self resonant operating principle. However the main downside of the design is that it employs a center tapped coil as the transformer, which makes the winding implementation a bit trickier. However the center tap allows an efficient push pull effect over the coil through just a couple of active devices such as mosfets.

As can be seen, there are fast recovery or high speed switching diodes connected across the gate/source of each mosfet. These diodes perform the important function of discharging the gate capacitance of the respective mosfets during their non-conducting states thereby making the switching operation snappy and quick.

You can use IRF540 as the mosfets which are rated at good 110V, 33amps. Heatsinks could be used for them, although the heat generated is not to any worrying level, yet still it's better to reinforce them on heat absorbing metals.

The inductor L2 terminating from center of the main induction coil is a kind of choke for eliminating any possible entry of the high frequency content into the power supply and also for restricting the current to safe limits.

Relatively the value of L2 should be high enough, a 2mH will do the job well. However it must be built using high gauge wires for enabling high current usage through it safely.

C1 and L1 constitute the tank circuit here for the interned high resonant frequency latching. Again these too musts be rated to withstand high magnitudes of current and heat.

Here we can see the incorporation of a 330nF/400V metalized PP capacitors.




Now comes L1, which is the most crucial element of the whole circuit. It must be built using extremely thick copper wires so that it sustains the high temperatures during the induction operations.
The capacitor as discussed above must be ideally connected as close as possible to the L1 terminals. his is important for sustaining the resonant frequency at the specified 200kHz frequency.

For the induction heater coil L1, many 1mm copper wire may be wound in parallel or in bifilar manner in order to dissipate current more effectively causing lower heat generation in the coil. Even after this the coil could be subjected to extreme heats, and could get deformed due to it therefore an alternative method of winding it may be tried.

In this method we wind it in the form of two separate coils joined at the center for acquiring the required center tap.

In this method lesser turns may be tried for reducing the impedance of  the coil and in turn increase its current handling capability. The capacitance for this arrangement may be in contrast increased in order to pull down the resonant frequency proportionately.
In all 330nF x 6 could be used for acquiring a net 2uF capacitance approximately.





Parts list for the above induction heater circuit or induction hot plate circuit

R1, R2 = 330 ohms 1/2 watt
D1, D2 = FR107 or BA159
T1, T2 = IRF540
C1 = 10,000uF/25V
C2 = 2uF/400V made by attaching 6nos 330nF/400V caps in parallel
D3----D6 = 25 amp diodes
IC1 = 7812
L1 = as given in the above schematic
L2 = 2mH choke made by winding 2mm magnet wire on any suitable ferrite rod
TR1 = 0-15V/20amps

POWER SUPPLY: Use regulated 15V 20 amp DC power supply.



Using BC547 transistors in place of high speed diodes

In the above induction heater circuit diagram we can see the mosfets gates consisting of fast recovery diodes, which might be difficult to obtain in some parts of the country.

A simple alternative to this may be in the form of  BC547 transistors connected instead of the diodes as shown in the following diagarm.

The transistors would perform the same function as the diodes since the BC547 can operate well around 1Mhz frequencies.





34 comments:

  1. Dear sir which diode can i put in place of FR107

    ReplyDelete
    Replies
    1. You can use BC547 transistor in place of the diodes. Connect base and collector together with the gate of the mosfet, and emitter to the drain of the other mosfet.

      Delete
  2. can i take L1 from another induction cooker ?

    ReplyDelete
    Replies
    1. No, only the specified type will work.

      Delete
    2. Hello sir can I use it for boiling a moving water from pipe.

      Delete
    3. Helo Salman,

      Yes you can do it, but the pipe should be made of iron or steel (magnetic material)

      Delete
    4. Thank you for the quick response,
      So pipe that Water flow inside, is a metal to be heated or as a induction metal(L1)?

      Delete
    5. The iron water pipe should pass through the center of the coil L1 as shown in the last diagram.

      Delete
  3. so do I calculate the power using the formula: VOLTAGE X CURRENT?

    ReplyDelete
  4. Not worked swgtm. the material not even heat up & both mosfets burnt out. it specified 200kHz frequency. So can i use Astable multivibrator to set frequency 200Khz to drive the coils.

    ReplyDelete
    Replies
    1. Hi Max,

      What did you use for D1/D2 and L2?

      Delete
    2. FR302 & 40 turns on a ferrite bead as L2

      Delete
  5. hello swagatam.
    Plz suggest a circuit to run cooling fan externally. i bought a amplifier unit the heat sense fan stops automatically after 1 minute. need a solid state cheap circuit to run fan directly from mains. (fan rated 12vdc 0.25amp 2.5w)

    ReplyDelete
    Replies
    1. Hello Max,

      The only solution is to a use a readymade 12V ac/dc smps adapter rated at 500mA or 1amp current, because you won't get below this rating.

      Delete
  6. Hello Swagatam,
    I have built my one successfully with DC power source of 18V connected to L2 while the other side keep 12V to drive MOSFET. I am also connecting ammerter in series to L2 to monitor the current. With some bolts and nuts or steel rod. They can turn red hot without problem. Current goes up from original L1 coil without anything inside to some level according to the object inside the coil. Somehow, I try this with 1/2" diameter steel pipe with 0.5mm thickness. Current goes up and increasing. After a while when pipe is in red hot, current suddenly increase very rapidly and FET burn-out. At this point, everything stop. I have to change FET as it was shorted Drain-Source. I used IRFP250N and diode BYV26E, pretty high rated voltage and current but still failed. Do you have any idea what I did wrong? Is this due to FET or Diode? Thanks.

    ReplyDelete
    Replies
    1. Helo Sitti,

      Try the following circuit, set Rt, Ct for getting 200khz, use L2 in place of "L" and the L1 for RL.

      http://homemadecircuitsandschematics.blogspot.in/2013/09/half-bridge-mosfet-driver-ic-irs21531d.html

      This circuit will never allow your mosfets to blow off, according to me.

      Delete
  7. Is there any alternative power supply? Cause its too expensive to buy a 20 A transformer then make it DC supply. By the way, could I use a power supply with adjuster in order to control the temparature of the induction coil?

    ReplyDelete
    Replies
    1. sorry there's no direct alternative for high current. You can reduce it proportionately by increasing the voltage, but that would also require modifications in the work coil, the turns will need to be increased while the gauge will need to reduced accordingly.

      Delete
    2. thanks for the quick reply, I really want to learn more about induction heating. Where I can find a choke coil required L2 because I can't find one of it in some electronics store here in my place, is it okay not to put L2? I want to share my idea to you, I have a circuit design that I found in the internet to control temperature, how can I share it to you?

      Delete
    3. You won't get the coils readymade, you will have to hand make it as per the details shown in the images and the article info.

      You are welcome to share your ideas, please send it to hitman2008@live.in

      Delete
  8. is it safe that my transformer that is rated 6A only is giving me up to 10A of current. Because i connected it to a bridge rectifier and a 4700uF caps to make a dc power supply, then i successfully make the circuit work but when I measured the current flowing to the transformer using a clamp meter, it gives me up to 10A depending on the metal to be heated. is it still safe for the transformer producing greater current than its rating?

    ReplyDelete
    Replies
    1. if it's showing more than the specified amps of the transformer means the voltage is being dropped proportionately in the course....so ultimately the total power is never being exceeded.

      as far as the above circuit is concerned, the coil would handle current depending upon its thickness, if it's correctly dimensioned it would be safe.

      Delete
  9. Replies
    1. It's 15V/20amp, that's equal to 300 watts

      Delete
    2. sir, i mean can i use 150v 2amp?

      Delete
    3. no, it should be @15V, amps is not important can be of any value (not less than 20amps)

      Delete
    4. Sir, both terminal will be +ve? if yes then; where is -ve terminal? And in MOSFET source will be grounded or -ve?

      Delete
    5. only the mosfet sources will go to the negative of the supply, no other point of the circuit is connected to the supply negative.

      Delete
    6. Sir, this kind of power supply(15v, 20a)is not esily available in the market.So, at which minimum voltage and current the circuit will be run?

      Delete
    7. Vinay, you can use a 12V, 20 amp transformer

      Delete
  10. Hello Swatam
    what changes I should make in the circuit to operate at 220V , two phases, each 110 V and a power of 6kW.
    and I'm thinking to cool L1 and L2 with water that circulates inside
    this is possible.

    ReplyDelete
    Replies
    1. Hello Paul,

      Sorry, I think that may not be recommended and could require more number of turns for L1/L2...I do not have the data for calculating those.

      Delete
  11. thank you very much.
    the number of turns can prove, but the electronic elements can recommend me what changes should be do.

    ReplyDelete
    Replies
    1. The configuration will remain as is. The resistors could be increased to 1K 10 watt (wirewound) each, everything will need to be done through trial and error, though.

      For the mosfets you can use IRF840, however since mains voltage is involved, the risks of an untoward could be on the cards, I am not recommending use of 220V for this project.

      Delete

Readers are requested not to include external links while commenting. For consulting a diagram, upload it on Google Drive and provide the link here.

Readers are advised to proceed with the construction of the presented circuits only after understanding the concepts from the core. Not adhering to this can lead to failures and frustrations.