1000 Watt induction heater boards

Discussion in 'Furnaces and their construction' started by Mark's castings, May 27, 2021.

  1. There's several cheap induction heater boards online in a wide variety of output powers: I bought a 1 kilowatt unit for $40 AUD delivered. Looking online a lot of people have used them with mixed success, you need to have water cooling through the 6mm O.D. copper tube and the supplied plated steel and brass clamps can be a source of poor contact that causes the circuit board's solder to melt. One guy on YouTube has experimented with tuning the frequency by adding extra turns to the work coil and extra capacitance to tune the resonant frequency down to 40 KHz to suit ferrous materials. The main caveat I've found so far is that you need a pretty solid power supply to drive the thing which can cost multiples of the actual heater unit. I'm at the point of mocking up the layout of the power supply which will be a 2500 Watt 48 Volt DC supply from junk laying around the workshop, like the power transformer and the filter capacitors. I expect to melt tiny amounts of metals but mainly be able to silver solder tungsten carbide to steel and heat treat 4140 steel.

    On the left is a 2500 VA transformer which has two 20 Volt windings (no load), a heatsink I'll mount the rectifier diodes to, some Sprague Powerlytic 80000 uF high current 40 Volt electrolytics. I'll have to wire a pair of electrolytics in series to increase the voltage rating at the expense of capacitance. Then I'll need a high current low voltage switch like a battery changeover.


    1KW induction 1.jpg
     
    Jason likes this.
  2. Jason

    Jason Gold

    Heady stuff! Way above the paygrade of this knuckledragger! We could really use something like this in the jewelry shop in Florida.;)
     
    Petee716 likes this.
  3. You can take the hard work out of the power supply by buying a 48 volt 20 amp switchmode supply for $150 off Ebay and then you just need to rig a fishtank pump to a bucket of water. Even if you fry a few getting up to speed they are pretty cheap and there's plenty of howto videos too.

    https://www.ebay.com.au/itm/4028228...rand=Unbranded&_trksid=p2047675.c101195.m1851
     
  4. spelter

    spelter Copper

    The capacity of the 1000w units may be pushed in the case of heat treating 4140, depending on size. 1000w isn't a fabulous amount of power, works for some uses because inductive heating is so easy to insulate. I think many hair driers are 1600w.

    Video of heating 1 inch iron with a 3000w capacity unit:
    Note the display shows power use at ~2200w.
     
  5. If I can silver solder small items with this initial unit I'll be happy. There's a guy whose work I've been following who has done some work on tuning the resonant circuit to better suit ferrous materials. He's able to melt 250 grams copper in ten minutes or so with an insulated crucible and 2.5KW of input power. A 240 Volt home circuit in Australia can draw up to 3.6KW so that would be the limit without a dedicated circuit.

     
  6. metallab

    metallab Silver

    I'd like to have an induction furnace as well. But what I see on Youtube (and other sites like this) is that they don't attain higher temps than 1200 C, which is also attainable with propane or even a Kanthal furnace.
    I'd like to use the real benefit of induction furnaces like inductrial ones which melt steel easily. Such devices can just be downscaled to sub kilogram quantities ?
     
  7. It's like any other furnace: if you can supply energy faster than it can escape, you can achieve practically any temperature. Induction furnaces have been used to melt platinum (1722 deg C) since 1922 when the first commercial units were sold. Nearly all of the smaller boards being sold are running at around 90KHz loaded, when around 40KHz and lower is preferred for steel. The guy whose video I linked above has a video showing how to tune the circuit to 40KHz by increasing the coil and capacitance of the tuned circuit.
     
  8. Now that the power supply is built I was able to give it a short test run: pretty much runs as advertised and heated a small steel bar to cherry red colour. The work coil got hot enough to change colour from the heat so there's enough current flowing to get 6mm copper tube appreciably hot. I'll have to rig the cooling fan to the circuit board and have a bucket of water to siphon through the coil before trying a serious run. These boards are pretty good value but won't be able to melt much of anything without insulation and precautions to pour fast into the mould. The power supply is completely made from junk lying around and I'm pleased to finally be able to use it all: The no-load voltage is 53 Volts DC which drops to 48.3 Volts at it's lowest during operation while heating something so it's exactly what the board makers specified: 48 Volts in operation and up to 56 Volts maximum.


    1KW induction operating 1.jpg

    1KW induction wired 1.jpg



    induction coil 1.jpg
     
  9. metallab

    metallab Silver

    The question is: Can you melt (stainless) steel with it or are there too many heat losses ?
     
  10. I'm going to use it for silver soldering tungsten carbide to steel for my lathe tools. I think the videos made by French creek valley linked above give a good idea of capabilities, melting up to 500 grams of copper in ten minutes with 2500 Watts in an insulated crucible.
     
    Jason likes this.
  11. metallab

    metallab Silver

    I have seen some ZVS powered inductors of 1000 to 2500 W on Amazon, they require 48 Volts, may run on lower, but there are no mains 230V based power supplies available which deliver an adjustable voltage to 48V with enough current (up till 40 A).
     
  12. This is the exact unit I'm using: 1KW ZVS heater Using some Morgan fibre insulation I stuck a 25mm long x 9mm diameter slug of 316 stainless in the coil and rigged up some fishtank tubing to a bucket on the bench flowing through the copper coil and siphoning into a bucket on the ground which is good for 5 minutes of cooling. I was able to measure up to 1200 degrees C with a thermocouple poked into contact with the stainless slug but the hair thin thermocouple wires literally burn out in the magnetic field despite giving a smooth accurate temperature reading (heater power on vs power off). I had to keep pulling the thermocouple out and hurriedly twisting a new junction about four times during the run. The LC tank circuit capacitors are quite hot and must be close to failing, really they should be using a foil construction capacitor rather than a cheaper film unit as the currents are causing excess heat. I'm going to make a PVC dielectric and aluminium foil capacitor similar to ones I've made before for spark gap tuned circuits in the past to get a good, reliable, low loss capacitor.

    The power supply doesn't need to be anything fancy, just a 48 Volt by 20 Amp DC supply and run the heater flat out on it. 48 Volts is a common telecommunications voltage so there's a lot of switchmode units on Ebay to choose from. I just happen to have suitable transformers in my junk collection that were handy.
     
    Last edited: May 30, 2021
  13. metallab

    metallab Silver

    Nice try ! Do you use an adjustable voltage power supply or just a fixed 48V one ?
    Measuring temperature can better be done with an infrared pyrometer gun. Measuring by a T/C contacting a solid surface is very unreliable. Moreover for 1200C a type K degrades rather quickly.
    Wrapping some Kaowool inside the coil will insulate the object to be heated much better and the coil gets less heat.
    Using a small pond pump with a bucket of water is also my idea, I use this for cooling at distillation.
     
  14. The Morgan fibre insulation I used to insulate the slug in the coil is comparable to Kaowool.

    If you look at the second photo of post number 8 you can see the power supply is everything on the white base board except for the induction heater unit: A 240 Volt to dual 19 Volt 2500VA transformer -> a 60 Amp full wave bridge rectifier made up of 8 x BYV44-500 dual diodes -> two 80 000 uF 40 Volt electrolytic capacitors wired in series to get a 40 000 uF by 80 Volt capacitor to filter the rectified 38 VAC to arrive at 53 Volts DC smoothed but unregulated. The supply is low enough impedance to only drop to 48.3 Volts when supplying the 20 Amps current.
     
  15. metallab

    metallab Silver

  16. Jason

    Jason Gold

    That sounds like the best reason for building one of these I've ever heard. ;) Practical, useful and will make life a whole lot easier. (remember my carbide glass breaking thing?)
    Everything comes full circle, some circles are just a little bigger!
     
  17. That would be almost powerful enough for 2KW if it's 40 Amps: 48 x 40 = 1920 Watts


    There's several videos on winding the heater coil into suitable shapes for everything from knife forging to soft soldering copper plumbing fittings, I was thinking of a compact coil with the 2-3 layers of turns in a small coil to give a compact heating zone. I found a source of very cheap, higher current motor run capacitors so I'll use an array of those to try and get the temperature down on the caps.

     
  18. metallab

    metallab Silver

    Can such a switching power supply be dimmed in order to lower the voltage ?
     
  19. Not unless it was built to do so, the easiest method to limit heating is to cut power to the induction heater with a PID temp controller and relay, assuming a stainless sheathed thermocouple is durable enough. The induction heater boards need a power supply with current capacity to spare and a sharp off to on voltage transition to begin oscillating reliably otherwise they will fry the driver MOSFETS.
     
  20. rocco

    rocco Silver

    There are power supplies which are adjustable, they're quite common and affordable for lower power outputs <500w, adjustable high powered units are harder to find and much more expensive.
     

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