Difference between revisions of "InductionHeater"

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(added a table for the inverter BOM)
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   {{Project
 
   {{Project
 
   |Name=InductionHeater
 
   |Name=InductionHeater
   |Status=Initializing
+
  |Picture=Hqdefault.jpg
   |Contact= smeding, gori
+
   |Status=In progress
 +
   |Contact= smeding
 
   }}
 
   }}
  
Idea is to make a 3kW induction spool to smelt metals and heat steel for forging.
+
We're working on an induction heater that can be used to heat anything conductive to high temperatures. The plan is to try to use it for forging steel and melting aluminum.
For examples see :
 
* [http://www.youtube.com/watch?v=0HdbKKvOiWU]
 
* [http://www.youtube.com/watch?v=l7fArOvXhQY]
 
  
==Inverter circuit==
+
Here are some examples of what a device like this is capable of:
 +
* [https://www.youtube.com/watch?v=0HdbKKvOiWU https://www.youtube.com/watch?v=0HdbKKvOiWU]
 +
* [https://www.youtube.com/watch?v=l7fArOvXhQY https://www.youtube.com/watch?v=l7fArOvXhQY]
  
Smeding had designed a circuit and made a BOM, see below:
+
== System design ==
 +
Induction heating works by applying a high-frequency magnetic field to the (conductive) workpiece being heated. Because of the [https://en.wikipedia.org/wiki/Skin_effect skin effect], conduction at these frequencies only occurs in a thin layer on the outside of the workpiece. This acts like the secondary winding of a transformer, allowing current to flow and heating the workpiece through resistive heating.
  
{|class="wikitable"
+
The design consists of the following parts:
!Component
+
* The power stage rectifies mains voltage, which is then chopped into a high-frequency 'modified square wave' with variable duty cycle and frequency.
!cost
+
* The coupling transformer transforms the relatively high-voltage, low-current square wave into a lower-voltage, high-current one, to ease the requirements on the work coil.
|-
+
* The work coil is where the workpiece is placed to be heated.
|Bridge rectifier
+
* The controller monitors relevant currents and voltages, and generates the waveforms that drive the power stage transistors.
|€2.56
 
|-
 
|switching transistor
 
|€22.92
 
|-
 
|Tank capacitors
 
|20.50
 
|-
 
|DC link filter capacitor
 
|€23.14
 
|-
 
|Gate driver
 
|€7.06
 
|-
 
|Couple transformer Toroid
 
|€20 (est.)
 
|-
 
|Gate drive transormer toroid
 
|€3
 
|-
 
|Estimate for components killed (see below)
 
|€60
 
|-
 
|'''Total'''
 
|€160
 
|}
 
  
Based on [http://local.roysmeding.nl/3kW_BOM.png| Smedings estimate]
+
=== Specs ===
Obviously, some parts may die a gruesome death during construction and testing. Worst case estimate is that the switching transistor and the driver will die twice, adding an amount of €60 to the BOM before we have a working machine.
+
* Input power: Standard single-phase mains: 230V RMS, 16A max ⇒ 3.5kVA
 +
* Frequency: 10 kHz - 100 kHz
 +
* 500A absolute maximum current in work coil
 +
* 'Modified square wave' control: variable frequency and duty cycle
  
 +
=== Controller ===
 +
The controller is based around a [http://www.st.com/content/st_com/en/products/microcontrollers/stm32-32-bit-arm-cortex-mcus/stm32f3-series/stm32f334.html STM32F334] ARM microcontroller. Its job is to generate the drive waveforms for the power stage, and display system status, based on measuring the relevant voltages and currents.
  
 +
=== Power stage ===
 +
[[File:Induction_heater_power_stage_schematic.png|1280px|The power stage schematic.]]
  
==Additional hardware==
+
Shown above is the schematic for the power stage. Mains voltage enters on the top left, where it is rectified and filtered to get approximately 325 V DC. Then, four IGBTs (IGBT1H, -1L, -2H, and -2L) form an H-bridge that generates the 10-100 kHz 'modified square wave' for the transformer.
  
 +
The IGBTs are driven via gate-drive transformers (GDT1 and GDT2) so that the control circuitry can be isolated from the high-voltage side. These transformers in turn are driven by high-current MOSFET drivers (IC1H, -1L, -2H, and -2L), which receive their signals from the controller.
  
In addition to the inverter circuit, at least the following things are needed to make a working induction heater
+
[[File:Induction_heater_power_stage_board_layout.png|512px|The power stage board layout.]]
{|class="wikitable"
+
[[File:Induction_heater_power_stage_board_assembled.jpg|768px|The assembled power stage board.]]
!Component
 
!cost
 
!Possible sources
 
!requirements
 
|-
 
|Coil
 
|€ 15 ?
 
|Gas tubing, car brake tubing
 
|Copper. Sufficient copper area to handle the current. Sufficient inner area + diameter to allow for effective cooling
 
|-
 
|heat exchanger
 
|€15 ?
 
|Car junkyard
 
|Unsure how much heat needs to be removed and at what temperatures. Worst Case would be 3 kW. A car radiator is probably good (cheap, sufficient power and an integrated fan)
 
|-
 
|Pump
 
|€
 
|Possibly a pump from a domestic heater (CV).  
 
|Have to check whether or not normal sizes create sufficient flow through  small diameter coil tubing
 
|-
 
|Electrical connections and wiring
 
|€
 
|Battery connections form scrapped cars?
 
|How much current do we expect, and how long do the wires have to be? how do we connect these to the coil tubing (Earth blocks?
 
|-
 
|...
 
|
 
|
 
|
 
|-
 
|'''Total cost'''
 
|€ 30 (incomplete)
 
|}
 
  
Now we need financing. Initial estimate is that  we need at least another 50% on top of the BOM to get the box, spiral, coolers etc. Goal is thus '''150 -200 euro'''
+
=== Coupling transformer ===
 +
The coupling transformer converts the high-voltage low-current chopped mains waveform to low voltage and high current for the work coil. Using a separate coupling transformer relaxes the requirements on the workpiece coil, so it can be adapted more easily to the workpiece being heated.
  
Pledges:
+
It'll be made from four stacked [https://www.aliexpress.com/item/Dark-Gray-Power-Transformers-Ferrite-Toroid-Cores-100mm-x-60mm-x-15mm/689128147.html 100 × 60 × 15 mm ferrite cores] (to provide enough core cross-sectional area for the magnetic field). The primary will consist of 60 turns of thick litz wire, and the secondary will be 2 turns of 15mm OD copper tubing, giving a winding ratio of 30:1.
 +
 
 +
== Pledges ==
 +
 
 +
So far, the following has been pledged:
 
* [[Gori]]: 50 euro
 
* [[Gori]]: 50 euro
 
* [[Flok]]: 10 euro
 
* [[Flok]]: 10 euro
 
* Walter: 50 евра
 
* Walter: 50 евра
* FooBar: €20
+
* FooBar: €20 cash betaald
 
* [[bertrik]]: €10
 
* [[bertrik]]: €10
* Semafoor: €20 (more if the project is better defined)
+
* Semafoor: €20  
 +
* [[Morphje]]: EUR 10 (and driving to the hardware store once)
 +
 
 +
Total pledges: €170

Latest revision as of 12:49, 1 October 2016

Project InductionHeater
Hqdefault.jpg
Status In progress
Contact smeding
Last Update 2016-10-01

We're working on an induction heater that can be used to heat anything conductive to high temperatures. The plan is to try to use it for forging steel and melting aluminum.

Here are some examples of what a device like this is capable of:

System design

Induction heating works by applying a high-frequency magnetic field to the (conductive) workpiece being heated. Because of the skin effect, conduction at these frequencies only occurs in a thin layer on the outside of the workpiece. This acts like the secondary winding of a transformer, allowing current to flow and heating the workpiece through resistive heating.

The design consists of the following parts:

  • The power stage rectifies mains voltage, which is then chopped into a high-frequency 'modified square wave' with variable duty cycle and frequency.
  • The coupling transformer transforms the relatively high-voltage, low-current square wave into a lower-voltage, high-current one, to ease the requirements on the work coil.
  • The work coil is where the workpiece is placed to be heated.
  • The controller monitors relevant currents and voltages, and generates the waveforms that drive the power stage transistors.

Specs

  • Input power: Standard single-phase mains: 230V RMS, 16A max ⇒ 3.5kVA
  • Frequency: 10 kHz - 100 kHz
  • 500A absolute maximum current in work coil
  • 'Modified square wave' control: variable frequency and duty cycle

Controller

The controller is based around a STM32F334 ARM microcontroller. Its job is to generate the drive waveforms for the power stage, and display system status, based on measuring the relevant voltages and currents.

Power stage

The power stage schematic.

Shown above is the schematic for the power stage. Mains voltage enters on the top left, where it is rectified and filtered to get approximately 325 V DC. Then, four IGBTs (IGBT1H, -1L, -2H, and -2L) form an H-bridge that generates the 10-100 kHz 'modified square wave' for the transformer.

The IGBTs are driven via gate-drive transformers (GDT1 and GDT2) so that the control circuitry can be isolated from the high-voltage side. These transformers in turn are driven by high-current MOSFET drivers (IC1H, -1L, -2H, and -2L), which receive their signals from the controller.

The power stage board layout. The assembled power stage board.

Coupling transformer

The coupling transformer converts the high-voltage low-current chopped mains waveform to low voltage and high current for the work coil. Using a separate coupling transformer relaxes the requirements on the workpiece coil, so it can be adapted more easily to the workpiece being heated.

It'll be made from four stacked 100 × 60 × 15 mm ferrite cores (to provide enough core cross-sectional area for the magnetic field). The primary will consist of 60 turns of thick litz wire, and the secondary will be 2 turns of 15mm OD copper tubing, giving a winding ratio of 30:1.

Pledges

So far, the following has been pledged:

  • Gori: 50 euro
  • Flok: 10 euro
  • Walter: 50 евра
  • FooBar: €20 cash betaald
  • bertrik: €10
  • Semafoor: €20
  • Morphje: EUR 10 (and driving to the hardware store once)

Total pledges: €170