Induction Heater 12 KW
This is an amazing induction heater and now you can build your own for fun or as a powerful tool.
schematics for building a 3 and 12kw unit. You'll be able to instantly melt steel aluminum and copper. You can use this for brazing, melting and forging metals. You can use this for casting, too. The tutorial covers theory, components and assembly of some of critical components. The tutorial is large. I will go over the main steps here to give you an idea of what goes into a project like this and how to design it so you don't blow any mosfets or IGBTs.
If you wish, you can refer to the link above. This Instructable presumes you have a good understanding of electronics and induction heaters. Let's begin.
The basic components are the inverter, driver, coupling transformer and RLC tank circuit. I'll show you the schematics in a little bit. Let's start with the inverter. This is an electrical device that changes the direction of DC current to AC current. For a high-power unit this must be robust. Above you can see the shielding that is used to protect the mosfet gate drive from any stray EMF. Stray EMF causes noise, which results in high-frequency switching. This leads to overheating and failure of the mosfet.
The high-current traces on the circuit board are underneath. Many layers of copper are used to allow them to carry over 50A of current. You do not want them overheating. Also note the large aluminum water-cooled heat sinks on each side. This is needed to remove the heat generated by the mosfets. I originally used fan-cooling, but to deal with this power I have small pond pumps moving plain water through the aluminum heat sinks. As long as the water is clean there should be no conduction. I also have thin mica pads underneath the mosfets to ensure there is no conduction through the sinks.
This is the schematic for the inverter. The circuit is really not that complicated. An inverted and non-inverted driver moves a 15v voltage high and low to set up an alternating signal in a gate-drive transformer (GDT). This transformer isolated the chips from the mofsets. The diode on the mosfet gate acts to limit spikes and the gate-drive resistor minimizes oscillations. Capacitor C1 removes any DC component. Ideally, you want the fastest rise and fall times on the gate, reducing heat. The resistor slows this down, which seems wrong. However, if the signal is not dampened you get overshoot and oscillations, which will destroy the mosfet. If you look up "snubber circuit" you will get more information.
Diodes D3 and D4 help protect the mosfets from reverse currents. C1 and C2 provide non-shorted pathways for the current to flow during the switching process. T2 is a current transformer so the driver, which we will talk about next, can get feedback about the current going to the tank.
Wow. That is one big schematic. Well, you can read about a simple, low-power inverter. If you want the big power you need a competent driver. This driver will lock onto the resonant frequency all by itself. As your metal melts it will stay locked onto the correct frequency without the need for any adjustment.
If you have ever built a simple induction heater with a PLL chip you probably recall tuning the frequency as your metal heats. You would watch the waveform move on the oscilloscope. You would keep changing the clocking frequency to maintain that perfect point. No need to do that anymore.
This circuit uses an Arduino microprocessor (uP) to follow the phase difference between the inverter voltage and the tank capacitor. Using this phase it calculates the the correct frequency using a C algorithm.
I will walk you through the circuit:
The tank capacitor signal comes in on the left to LM6172. This is a high-speed inverter that converts the signal to a nice, clean square-wave. Got to be clean. This signal is then isolated using the optical isolator, FOD3180. These isolators are key! This signal goes to the PLL through the PCAin input. This is compared to the inverter signal on PCBin, which drives the inverter from VCOout. The Arduino finely controls the PLL clock using a 1024-bit pulse-width modulated signal. The two-stage RC filter converts the PWM signal into a simple analog voltage that goes in at VCOin.
How does the Arduino know what to do? Magic? A good guess? No. It gets the phase-difference information about PCA and PCB from PC1out. R10 and R11 limit the voltage within 5 voltage for the Arduino, and the two-stage RC filter cleans the signal from any noise. We want spanking clean signals because we don't want to pay more money for expensive mosfets after they blow up from noisy inputs.
That was a lot of information. You may be asking yourself do you need such a fancy circuit? The answer is "it depends". If you want a self-tuning circuit then the answer is yes. If you want to manually tune the frequency then the answer is no. You can build a very simple driver with just a 555 timer and use an oscilloscope. You can get a little more sophisticated and add a PLL (phase-lock-loop) chip.
Wow. That is one big schematic. Well, you can read about a simple, low-power inverter. If you want the big power you need a competent driver. This driver will lock onto the resonant frequency all by itself. As your metal melts it will stay locked onto the correct frequency without the need for any adjustment.
If you have ever built a simple induction heater with a PLL chip you probably recall tuning the frequency as your metal heats. You would watch the waveform move on the oscilloscope. You would keep changing the clocking frequency to maintain that perfect point. No need to do that anymore.
This circuit uses an Arduino microprocessor (uP) to follow the phase difference between the inverter voltage and the tank capacitor. Using this phase it calculates the the correct frequency using a C algorithm.
I will walk you through the circuit:
The tank capacitor signal comes in on the left to LM6172. This is a high-speed inverter that converts the signal to a nice, clean square-wave. Got to be clean. This signal is then isolated using the optical isolator, FOD3180. These isolators are key! This signal goes to the PLL through the PCAin input. This is compared to the inverter signal on PCBin, which drives the inverter from VCOout. The Arduino finely controls the PLL clock using a 1024-bit pulse-width modulated signal. The two-stage RC filter converts the PWM signal into a simple analog voltage that goes in at VCOin.
How does the Arduino know what to do? Magic? A good guess? No. It gets the phase-difference information about PCA and PCB from PC1out. R10 and R11 limit the voltage within 5 voltage for the Arduino, and the two-stage RC filter cleans the signal from any noise. We want spanking clean signals because we don't want to pay more money for expensive mosfets after they blow up from noisy inputs.
That was a lot of information. You may be asking yourself do you need such a fancy circuit? The answer is "it depends". If you want a self-tuning circuit then the answer is yes. If you want to manually tune the frequency then the answer is no. You can build a very simple driver with just a 555 timer and use an oscilloscope. You can get a little more sophisticated and add a PLL (phase-lock-loop) chip.
There are a few approaches for this part. If you want a high-power heater you will need to have a capacitor array to handle the current and voltage.
First, you need to determine what operating frequency you will use. Higher frequencies have greater skin effect (less penetration) and are good for smaller objects. Lower frequencies are better for larger objects and have greater penetration. Higher frequencies have greater switching losses, but there is less current going through the tank. I choose a frequency near 70khz and wound up with about 66khz. My capacitor bank is 4.4uf and can handle over 300A. My coil is near 1uH. The capacitors are from Illinois Capacitors. They are pulse film capacitors. They are axial lead, self healing metallized polypropylene, high voltage, high current, and high frequency. Mine are 0.22uf/3000vdc. The model number is 224PPA302KS.
I used two copper bus bars and drilled matching holes on each side. I used plumber's solder and fixed the capacitors to the bars. I then ran copper tubing on each side to carry cold water to the coil.
Do not get cheap capacitors. They will self-destruct and you will pay more money than if you did the right thing the first time. Here is another thought. You can buy a Celem capacitor. Although they are expensive, the cost is not that far off from the cost of building a good capacitor array. Trust me, I've been there already.
I've posted a picture of a Celem capacitor for your viewing pleasure.
Please note that the Celem is water-cooled. Whether you use the Celem or make your own you need to water-cool these units. I use the same pump to cool the capacitor as I use to cool the work-coil.
Induction Heater 12 KW
This is an amazing induction heater and now you can build your own for fun or as a powerful tool.
schematics for building a 3 and 12kw unit. You'll be able to instantly melt steel aluminum and copper. You can use this for brazing, melting and forging metals. You can use this for casting, too. The tutorial covers theory, components and assembly of some of critical components. The tutorial is large. I will go over the main steps here to give you an idea of what goes into a project like this and how to design it so you don't blow any mosfets or IGBTs.
If you wish, you can refer to the link above. This Instructable presumes you have a good understanding of electronics and induction heaters. Let's begin.
The basic components are the inverter, driver, coupling transformer and RLC tank circuit. I'll show you the schematics in a little bit. Let's start with the inverter. This is an electrical device that changes the direction of DC current to AC current. For a high-power unit this must be robust. Above you can see the shielding that is used to protect the mosfet gate drive from any stray EMF. Stray EMF causes noise, which results in high-frequency switching. This leads to overheating and failure of the mosfet.
The high-current traces on the circuit board are underneath. Many layers of copper are used to allow them to carry over 50A of current. You do not want them overheating. Also note the large aluminum water-cooled heat sinks on each side. This is needed to remove the heat generated by the mosfets. I originally used fan-cooling, but to deal with this power I have small pond pumps moving plain water through the aluminum heat sinks. As long as the water is clean there should be no conduction. I also have thin mica pads underneath the mosfets to ensure there is no conduction through the sinks.
This is the schematic for the inverter. The circuit is really not that complicated. An inverted and non-inverted driver moves a 15v voltage high and low to set up an alternating signal in a gate-drive transformer (GDT). This transformer isolated the chips from the mofsets. The diode on the mosfet gate acts to limit spikes and the gate-drive resistor minimizes oscillations. Capacitor C1 removes any DC component. Ideally, you want the fastest rise and fall times on the gate, reducing heat. The resistor slows this down, which seems wrong. However, if the signal is not dampened you get overshoot and oscillations, which will destroy the mosfet. If you look up "snubber circuit" you will get more information.
Diodes D3 and D4 help protect the mosfets from reverse currents. C1 and C2 provide non-shorted pathways for the current to flow during the switching process. T2 is a current transformer so the driver, which we will talk about next, can get feedback about the current going to the tank.
Wow. That is one big schematic. Well, you can read about a simple, low-power inverter. If you want the big power you need a competent driver. This driver will lock onto the resonant frequency all by itself. As your metal melts it will stay locked onto the correct frequency without the need for any adjustment.
If you have ever built a simple induction heater with a PLL chip you probably recall tuning the frequency as your metal heats. You would watch the waveform move on the oscilloscope. You would keep changing the clocking frequency to maintain that perfect point. No need to do that anymore.
This circuit uses an Arduino microprocessor (uP) to follow the phase difference between the inverter voltage and the tank capacitor. Using this phase it calculates the the correct frequency using a C algorithm.
I will walk you through the circuit:
The tank capacitor signal comes in on the left to LM6172. This is a high-speed inverter that converts the signal to a nice, clean square-wave. Got to be clean. This signal is then isolated using the optical isolator, FOD3180. These isolators are key! This signal goes to the PLL through the PCAin input. This is compared to the inverter signal on PCBin, which drives the inverter from VCOout. The Arduino finely controls the PLL clock using a 1024-bit pulse-width modulated signal. The two-stage RC filter converts the PWM signal into a simple analog voltage that goes in at VCOin.
How does the Arduino know what to do? Magic? A good guess? No. It gets the phase-difference information about PCA and PCB from PC1out. R10 and R11 limit the voltage within 5 voltage for the Arduino, and the two-stage RC filter cleans the signal from any noise. We want spanking clean signals because we don't want to pay more money for expensive mosfets after they blow up from noisy inputs.
That was a lot of information. You may be asking yourself do you need such a fancy circuit? The answer is "it depends". If you want a self-tuning circuit then the answer is yes. If you want to manually tune the frequency then the answer is no. You can build a very simple driver with just a 555 timer and use an oscilloscope. You can get a little more sophisticated and add a PLL (phase-lock-loop) chip.
Wow. That is one big schematic. Well, you can read about a simple, low-power inverter. If you want the big power you need a competent driver. This driver will lock onto the resonant frequency all by itself. As your metal melts it will stay locked onto the correct frequency without the need for any adjustment.
If you have ever built a simple induction heater with a PLL chip you probably recall tuning the frequency as your metal heats. You would watch the waveform move on the oscilloscope. You would keep changing the clocking frequency to maintain that perfect point. No need to do that anymore.
This circuit uses an Arduino microprocessor (uP) to follow the phase difference between the inverter voltage and the tank capacitor. Using this phase it calculates the the correct frequency using a C algorithm.
I will walk you through the circuit:
The tank capacitor signal comes in on the left to LM6172. This is a high-speed inverter that converts the signal to a nice, clean square-wave. Got to be clean. This signal is then isolated using the optical isolator, FOD3180. These isolators are key! This signal goes to the PLL through the PCAin input. This is compared to the inverter signal on PCBin, which drives the inverter from VCOout. The Arduino finely controls the PLL clock using a 1024-bit pulse-width modulated signal. The two-stage RC filter converts the PWM signal into a simple analog voltage that goes in at VCOin.
How does the Arduino know what to do? Magic? A good guess? No. It gets the phase-difference information about PCA and PCB from PC1out. R10 and R11 limit the voltage within 5 voltage for the Arduino, and the two-stage RC filter cleans the signal from any noise. We want spanking clean signals because we don't want to pay more money for expensive mosfets after they blow up from noisy inputs.
That was a lot of information. You may be asking yourself do you need such a fancy circuit? The answer is "it depends". If you want a self-tuning circuit then the answer is yes. If you want to manually tune the frequency then the answer is no. You can build a very simple driver with just a 555 timer and use an oscilloscope. You can get a little more sophisticated and add a PLL (phase-lock-loop) chip.
There are a few approaches for this part. If you want a high-power heater you will need to have a capacitor array to handle the current and voltage.
First, you need to determine what operating frequency you will use. Higher frequencies have greater skin effect (less penetration) and are good for smaller objects. Lower frequencies are better for larger objects and have greater penetration. Higher frequencies have greater switching losses, but there is less current going through the tank. I choose a frequency near 70khz and wound up with about 66khz. My capacitor bank is 4.4uf and can handle over 300A. My coil is near 1uH. The capacitors are from Illinois Capacitors. They are pulse film capacitors. They are axial lead, self healing metallized polypropylene, high voltage, high current, and high frequency. Mine are 0.22uf/3000vdc. The model number is 224PPA302KS.
I used two copper bus bars and drilled matching holes on each side. I used plumber's solder and fixed the capacitors to the bars. I then ran copper tubing on each side to carry cold water to the coil.
Do not get cheap capacitors. They will self-destruct and you will pay more money than if you did the right thing the first time. Here is another thought. You can buy a Celem capacitor. Although they are expensive, the cost is not that far off from the cost of building a good capacitor array. Trust me, I've been there already.
I've posted a picture of a Celem capacitor for your viewing pleasure.
Please note that the Celem is water-cooled. Whether you use the Celem or make your own you need to water-cool these units. I use the same pump to cool the capacitor as I use to cool the work-coil.
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