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 Silver 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 Silver 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 Silver 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.
     
  12. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Me too, but here's the rub. Recently, I've seen a number of posts about how much more efficient induction furnaces are. My question would be compared to what?...and for doing what?

    If you are melting ferrous metals and have a system well suited and tuned for doing such, I would say yes, they are very efficient and attractive.

    If you are melting nonferrous metals, maybe not so much, compared to resistive electric. For resistive electric, I can assure you a very high percentage of power input is converted to melt energy and the inefficiency is having to also heat the furnace mass on the first melt. A low mass furnace minimizes this. Once the furnace mass is heated, the loss from a well insulated furnace is very low. Both resistive electric and induction must heat a conductive crucible for the majority of heat transfer to the melt, which is a loss in the crucible mass and heat loss from the surfaces that do not go directly into the melt.

    For ferrous metals a very high percentage of energy can go directly into the melt and non conductive crucibles are possible.

    Here is the biggest issue for me; even though the total power required for a non-ferrous melts may be comparable between resistive and induction, all the recommendations I receive for comparable melting capacity will require 4-6x the service power for the induction system, albeit for a similarly shorter melt time. For me, and I suspect most hobbyists, that poses quite the dilemma, because for me that equates to 35-50kw system. 3DTOPO mentioned in a previous post that the induction system only draws a fraction of its rated melting energy but I have not been able to confirm that through manufacturers recommendations. The cost of such a system, even imports is nontrivial.

    Also, trying to use lower power inductions systems over longer periods of time (at least in extreme 4x) appears to be problematic and unviable because of inductive loads and circuit designs.

    I have a 200amp 240vac service in my shop and 50kw would exceed that and even the 35kw creates some serious issues of practicality for a portable melter. I just can't dedicate that much foundry space inside my shop and even if I could, it poses too great of a fire hazard.

    I can melt ~16lbs (a cold charged A20) of aluminum in under an ~45min from cold start in my low mass resistive electric for about 50-75 cents worth of power cost. As a stretch, it could do bronzes. Iron is out of the question. I can melt 60lbs of Aluminum with longer times. Is reducing a 16lb non-ferrous melt time to 10-15 minutes worth the overhead and complexity of induction?........not for me. But the ability to melt higher temp metals is still of great interest........so it remains a continuing interest.

    Now, if you're satisfied with small melts of a kg or so, or you're blessed with a large high voltage power source, you may not feel so constrained.

    -All that glitters is not gold.

    Best,
    Kelly
     
    Meteor Monowatt likes this.
  13. DavidF

    DavidF Administrator Staff Member Banner Member


    Keeping things short, for me I would be looking to melt small amounts of ferris alloys (approximately 5 lbs) like stainless, alloy steels, and titanium. I would need to familiarize myself more with the induction melting of these metals before I put any money on the line.
    But after working 24 hours on 4 hours of sleep, my mind just isn't up to the task....
     
  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks David, I was just quoting you because of shared interest, but it's really an open question and set of subjects for the forum. I'll start a new thread.

    Best,
    Kelly
     
  15. DavidF

    DavidF Administrator Staff Member Banner Member


    Just a few years ago it's likely we would had no interest in induction melting... but now we all have seen the great possibilities with the technologies that are available to us now.
    But we are still hesitant to make a move before gathering more information, knowledge, and experience...or atleast I am.
    Thanks for starting the new thread Kelly, I'll be watching it ;)
     

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