Can you put your finger in an induction heater?

Many of you who are reading this may be asking "What is a ZVS driver"? Well, it is an extremely efficient oscillator circuit that is able to create an extremely powerful electromagnetic field that heats up the metal. It is the backbone of the induction heater that this instructable is showing you how to make.

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To understand how this power supply works, I will explain the different sections of it. The first section is the 24 volt power supply. The power supply needs to produce 24 volts at a current of 10 amps. For my power supply, I will be using two sealed lead acid batteries wired in series. The power is then fed into the ZVS driver board. The ZVS oscillator pushes and pulls current though a coil around the object that is being heated. This constant changing of the current's direction creates a fluctuating magnetic field. This induces many small eddy currents in the metal(refer to the diagram above). All of these currents are relatively high, and because of the low resistance of the target metal, heat is generated. According to ohms law, power converted to heat in a resistive circuit is P=I^2*R.

Now, the metal type of the object that is being heated is very important. Ferrous metals have a higher magnetic permeability, so they are able to harness more energy from the magnetic field. This allows them to be heated quicker than other materials. Metals, like aluminum, have a lower magnetic permeability, so it takes longer for them to heat up. Things that have a high resistance and low magnetic permeability, like a human finger, will not be heated at all by an induction heater. The resistance of the material is also very important. If you have a higher resistance in the target metal, then less current will flow, so the power converted to heat gets exponentially smaller. If you have a metal with a lower resistance, then the current will be higher, but power loss will be lower due to ohms law. It is a little bit complicated, but because of the relationship between resistance and power output, the highest power output is achieved when the resistance of the object approaches 0.

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Additional reading:
Revolutionizing Water Heating: Is Magnetic Induction Worth it?

The ZVS oscillator is the most complex part of this circuit, so I am going to explain how it works. First of all, when the current is switched on, it flows though 2 inductive chokes into each side of the coil. The choke is to make sure the circuit does not draw to much amperage on start up. The current also flows thought the two 470 ohm resistors into the gates of the two Mosfets. Now, because no component is perfect, one Mosfet is going to turn on first. When this happens, it hogs all the gate current from the other Mosfet. It will also draw the drain of that Mosfet that is on to ground. This will not only let current flow though the coil to ground, but it will also let current flow though one of the fast diodes form the other gate of the other Mosfet, locking it off. Because there is a capacitor in parallel with the coil, it creates a resonant tank circuit that starts oscillating. Because of this resonant action, the drain of the other Mosfet will swing back and forth in its voltage, eventually reaching 0 volts. Once this voltage is reached, the gate charge from the Mosfet that is on will discharge though the fast diode into the drain of the opposite Mosfet, effectivly shutting it off. With this Mosfet off, the other Mosfet has the opportunity to turn on. After this, the cycle repeats thousands of times per second. The 10K resistor is meant to deplete any excess gate charge on the Mosfet, because it is like a capacitor, and the Zener diode is meant to keep the gates of the mosfets at 12 volts or under so they do not explode. This high frequency high power oscillator is what allows metal objects to be heated.

Now, its time to build this thing!

Induction heater is a fun project. I built a small induction heater then I wanted a more powerful one. A small unit is so simple you can build it in about 2 hours work. A larger more powerful unit will take longer. If you take your induction camping it works great to run it on your 12v car battery.

I built my largest induction heater from a microwave oven transformer. Remove the v secondary coil, replace it with enough #12 solid copper wire to get 12v to 15vdc. I have about 15 MOTs they all have 100 turns on the primary coil. Math is easy for the secondary coil running on 120vac on the primary = about .833 vac per turn on the secondary.

I have not experimented with a flat induction coil the value must be 2. uh minimum value. Buy a, resistor, capacitor, inductor, meter about $35. on ebay to test your coils. The choke coil needs to be large enough not to saturate or it will stop working at a certain power range then current suddenly goes to maximum then mosfets explode. Very low internal mosfet resistance works best it prevents mosfets from over heating easy.

Here is my induction circuit, leave off the transformers so you can run it on a car battery if that is what you want. My small induction heater will heat a 1/4" steel rod red hot in about 3 minutes. My w induction heater heats a 1/4" steel rod red hot in 7 seconds. You don't need w to heat food it will burn before food has time to cook.

My induction heaters all have the same circuit drawing for the exception of larger power supplies and larger L2 choke coil for higher power units. If you change #10 circuit copper wire to a smaller wire skin effect goes up and the circuit efficiency goes down. My induction heat is several times smaller than the w power supply as you can see in the photos.

Be sure to connect the caps in a box shape like a Rail Gun cap bank charge and discharge is much faster. Build the small unit with the 6 yellow color caps first. I use insulated Romex solid copper house wire. Be sure to use insulated wire if you accidently touch the osc coil with metal osc stops then 1 of the mosfets will explode.

You can build the small circuit for $15. The larger circuit only cost be extra for a 100a bridge rectifier and the meter. I salvage parts from old TV and old computer power supplies. 10 mosfets are $6 free shipping on ebay if you order from a seller in China.

If you have not built an induction heater yet it is a fun project. Build the small circuit with 6 yellow capacitors first.Induction heater is a fun project. I built a small induction heater then I wanted a more powerful one. A small unit is so simple you can build it in about 2 hours work. A larger more powerful unit will take longer. If you take your induction camping it works great to run it on your 12v car battery.I built my largest induction heater from a microwave oven transformer. Remove the v secondary coil, replace it with enough #12 solid copper wire to get 12v to 15vdc. I have about 15 MOTs they all have 100 turns on the primary coil. Math is easy for the secondary coil running on 120vac on the primary = about .833 vac per turn on the secondary.I have not experimented with a flat induction coil the value must be 2. uh minimum value. Buy a, resistor, capacitor, inductor, meter about $35. on ebay to test your coils. The choke coil needs to be large enough not to saturate or it will stop working at a certain power range then current suddenly goes to maximum then mosfets explode. Very low internal mosfet resistance works best it prevents mosfets from over heating easy.Here is my induction circuit, leave off the transformers so you can run it on a car battery if that is what you want. My small induction heater will heat a 1/4" steel rod red hot in about 3 minutes. My w induction heater heats a 1/4" steel rod red hot in 7 seconds. You don't need w to heat food it will burn before food has time to cook.My induction heaters all have the same circuit drawing for the exception of larger power supplies and larger L2 choke coil for higher power units. If you change #10 circuit copper wire to a smaller wire skin effect goes up and the circuit efficiency goes down. My induction heat is several times smaller than the w power supply as you can see in the photos.Be sure to connect the caps in a box shape like a Rail Gun cap bank charge and discharge is much faster. Build the small unit with the 6 yellow color caps first. I use insulated Romex solid copper house wire. Be sure to use insulated wire if you accidently touch the osc coil with metal osc stops then 1 of the mosfets will explode.You can build the small circuit for $15. The larger circuit only cost be extra for a 100a bridge rectifier and the meter. I salvage parts from old TV and old computer power supplies. 10 mosfets are $6 free shipping on ebay if you order from a seller in China.

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