Homemade induction melter.

Discussion in 'Furnaces and their construction' started by Ironsides, Nov 21, 2021.

  1. Ironsides

    Ironsides Silver

    If you have a need to melt small amounts of steel quickly watch this video. I do have some of the expensive parts needed to build this melter that I got from hard rubbish days but this method was very hit and miss at best of times. One of these days I may get around to making an induction melter. So I discovered an Aussie guy that dismantles large V.F.Ds for scrap metal so if you live in Australia he is the go to guy to get most of the components for a induction melter. He has a video of him dismantling a large V.F.D.

     
  2. metallab

    metallab Silver

    With a DC welder and carbon rods you can also tiny (100g) amounts of (stainless) steel. I alloyed SS 304 my electric arc melting the mild steel, chrome and nickel together and made a few castings.
    But an induction furnace is on my bucket list when they become affordable and reliable. The latter especially as the DIY kits sold by Amazon or ebay for less than a few hundred dollars are without 48 Volts power supply and without overcurrent protection which can fry the MOSFETs. I am not an electronics engineer, but just a 'dumb user' of electronics.
     
  3. DavidF

    DavidF Administrator Staff Member Banner Member

    I'm definitely interested in one, but building one might be a little beyond me...
     
  4. Ironsides

    Ironsides Silver

    I have watched plenty of homemade induction heater videos and all except one knows how to use one. This is the reason why they destroy the mosfets. To give you an example, your car engine is rated in kilowatts. If you run the car at the maximum kilowatt rating all the time the engine will have a short life. This is why car engines last a long time because they always run at a low output. It is the same thing when using mosfets, just because the specs say the maximum amps is say 10 amps at 600 volts and is run all the time at those specs it will have a short life. To use an induction heater a amp meter and kilowatt meter are essential items to know if you are exceeding the power rating of the mosfets. Overcurrent protection is used when overload current exceeds the mosfet specs but if you keep on overloading the induction heater the overload protection will work maybe a few times but the mosfets will fail without warning because they are very sensitive to overload. Now you can see that it is essential to know what is happening in the induction heater and how it prevents mosfet failure. One of the biggest reasons why these homemade induction heaters fail is the user fails to understand that steel has very little resistance at room temperature. So when they put a tiny screw in the heater coil it heats up quickly because it has a small mass. So they then put in a steel rod that has a high mass and wait for the steel to heat up. That extra time needed to heat up the steel is a serious overload to the mosfet. When steel heats up the resistance increases and the load on the mosfets drops but if the mosfet has not got a higher rating to handle that load it will fail. This a very simple explanation as to why mosfets fail. If you have the time watch frenchcreekvalley videos on youtube, he is a electrical engineer and with all the meters he is using he knows exactly what is going on in his internet purchased induction heater.
     
  5. metallab

    metallab Silver

    Good explanation, luckygen1001 !
    But I already thought it are mostly user errors that mosfets burn out. E.g this affordable one, including a 48V power supply is tempting for me.
    https://www.ebay.com/itm/283961337967?hash=item421d6a286f:g:89sAAOSwRFldUmiQ&LH_BIN=1
    But when I e.g. put some steel into it and the mosfet gets overloaded I can say goodbye to it.
    So I additionally need an ammeter and a wattmeter (cheap electronics) and at least a circuit breaker in the 48V circuit which trips when the iron to be melted drags too much power.
     
  6. BattyZ

    BattyZ Copper Banner Member

    I bought a 2500W unit and corresponding PSU. Here are 2 test LF pours.



    Tried for almost half a day to get a full crucible of copper but was unsuccessful. Just not enough juice I believe. Aluminum, however, it just eats through. The crucible is quite tiny for doing any castings though. For little knick-knacks or pieces of hardware, it would be great.

    I was really hoping to go down the induction route since I have 3 phase at my shop, but like Ironsides mentioned, you do have to have more machine than you will ever use. For my melt size that would be costly right now. I have 1 out of 3 coils wound and installed for a 3 phase kiln so it will be interesting to see how that compares to the industry standard melt time of 45 minutes.
     
  7. metallab

    metallab Silver

    Weird that even a 2500W induction furnace is unable to melt even a small amount of copper. Even my 1500W Kanthal resistance furnace melts 500g Cu metal in 40 minutes. An induction furnace should it do within at most this time span.
     
  8. BattyZ

    BattyZ Copper Banner Member

    I could definitely be doing something wrong. lol I tried different things but only so many ways one can add metal. Was doing it a wire at a time, looked like I had a full crucible. Went to pour and only the center and top were liquid.

    My build is aiming for 10.5KW in my resistance furnace. Hopefully, I have linearly scaled results!
     
  9. Ironsides

    Ironsides Silver

    I made an induction furnace from a microwave oven power supply. It melted pewter really fast but it was really slow melting a zinc alloy. So I tried to melt aluminium and it started to melt but it froze as I added more aluminium. I tried to speed things up by adding full power but it destroyed the power supply. I have a good idea as to what the problem was but it is beyond my skill set to fix.
     
  10. BattyZ

    BattyZ Copper Banner Member

    After the failed attempts I was thinking of what could be done. If there was a second 2500w setup and you wound the coils only half the turns and stacked them would that double the power? You could do 4 sets this way at roughly $800 but that is fast approaching the price of a 15kw fleabay induction melter. Just a thought.
     
  11. Ironsides

    Ironsides Silver

    If you reduce the number of coils you are altering how the circuit works. If you want to, take out half the coils in a transformer on the 115 volt side and then plug it into the wall and see what happens. The best case would be the circuit breaker tripping and the worst case would be smoke coming from the transformer.
     

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