Induction Heater testing
IamSmooth, Mon Nov 09 2009, 01:53AMWell, the good news is I have gotten a 1/4" nut to glow bright orange for several minutes without overheating my mosfets. I seem, though, to have hit a wall in getting it hotter.
My unit is a half-bridge using 170vdc as the power input. The design is similar to
except the inverter output goes to a 20 turn step-down transformer which encircles one of the legs of my LC series tank. The work coil is 2" diameter 3/8" copper pipe with 5 turns. The capacitor is a bank for a total of 1.0uf.
I tune the resonance manually with a pot. I find that right at resonance it flips back and forth, and I have to adjust the pot to stay there, especially if I am near 170v input. My work coil is attached to one side of the capacitor bank, so the capacitors don't share the current equally, but they don't get too hot. I don't know if this is a big deal.
Would heating the nut in a crucible instead of open air help? where can I get one?
Would adding a PLL help, or should manual tuning work well enough?
Would decreasing the turns on the step-down transformer allow me to get more current into the tank?
Thanks.
Re: Induction Heater testing
Myke, Mon Nov 09 2009, 02:00AM
I think you can't get it hotter because you reached the curie point making the nut no longer magnetic.
I don't know how much a crucible would help you once you reached the curie point. I'd think it wouldn't do much because it will have trouble getting above the point where it's no longer magnetic.
Myke, Mon Nov 09 2009, 02:00AM
I think you can't get it hotter because you reached the curie point making the nut no longer magnetic.
I don't know how much a crucible would help you once you reached the curie point. I'd think it wouldn't do much because it will have trouble getting above the point where it's no longer magnetic.
Re: Induction Heater testing
IamSmooth, Mon Nov 09 2009, 02:51AM
I've seen videos of the metal glowing white and sparking, so there is room to get it hotter.
IamSmooth, Mon Nov 09 2009, 02:51AM
I've seen videos of the metal glowing white and sparking, so there is room to get it hotter.
Re: Induction Heater testing
Myke, Mon Nov 09 2009, 04:07AM
I should have said "It gets a lot harder to heat it hotter than curie point because you don't have hysteresis losses anymore". I think you would have to heat it up hotter with resistive losses after the curie point. I'm not completely sure though.
Myke, Mon Nov 09 2009, 04:07AM
I should have said "It gets a lot harder to heat it hotter than curie point because you don't have hysteresis losses anymore". I think you would have to heat it up hotter with resistive losses after the curie point. I'm not completely sure though.
Re: Induction Heater testing
Gabriel35, Thu Nov 12 2009, 06:58PM
Hi Iam, i was trying to build a IH too, and then i finally got mine to work, with danyk's schematic
works pretty nice
i like to tune it manually, is a way of getting entertainment while watching the screw becoming white...if you like this too, you'll probably like to try this circuit....the IGBT's used are not with anti-paralel diodes inside, so if you can get acess to some diode protected IGBT, you can get rid of the Turbo diode drawed..
Gabriel35, Thu Nov 12 2009, 06:58PM
Hi Iam, i was trying to build a IH too, and then i finally got mine to work, with danyk's schematic
works pretty nice
i like to tune it manually, is a way of getting entertainment while watching the screw becoming white...if you like this too, you'll probably like to try this circuit....the IGBT's used are not with anti-paralel diodes inside, so if you can get acess to some diode protected IGBT, you can get rid of the Turbo diode drawed..
Re: Induction Heater testing
Tonskulus, Sat Nov 21 2009, 05:52PM
I would say you will need at least 1kW of power to melt some small steel/iron pieces. My induction heater is limited to 3kW wall outlet so far and it can melt some 10mm thick steelbars @ 10A/230V input.
However, we need actually lots of circulating reactive power.
Tonskulus, Sat Nov 21 2009, 05:52PM
I would say you will need at least 1kW of power to melt some small steel/iron pieces. My induction heater is limited to 3kW wall outlet so far and it can melt some 10mm thick steelbars @ 10A/230V input.
However, we need actually lots of circulating reactive power.
Re: Induction Heater testing
paolss, Wed Dec 02 2009, 07:26PM
Hello all.
Tonskulus i want to ask You a question.
I want to modify my circuit to work with 220VAC so this will be 310 to 350VDC
I use IRFP460 mosfet transistors.
And now all is working perfect with 154VDC so i have almost 400VAC on "work coil"
And i think if i will use 310VDC i can have max from 974VAC to 1099VAC on work coil.
So do i need to have mosfets minimum 550V / 600V ? or more ? IGBT 1200V ?
Can You tell me what i need also to change - because i want to know more before i "blow" some mosfets :)
Thanks.
my current circuit:
paolss, Wed Dec 02 2009, 07:26PM
Hello all.
Tonskulus i want to ask You a question.
I want to modify my circuit to work with 220VAC so this will be 310 to 350VDC
I use IRFP460 mosfet transistors.
And now all is working perfect with 154VDC so i have almost 400VAC on "work coil"
And i think if i will use 310VDC i can have max from 974VAC to 1099VAC on work coil.
So do i need to have mosfets minimum 550V / 600V ? or more ? IGBT 1200V ?
Can You tell me what i need also to change - because i want to know more before i "blow" some mosfets :)
Thanks.
my current circuit:
Re: Induction Heater testing
Experimentonomen, Sat Mar 19 2011, 09:27PM
Im back again and i have a new induction heater project.
This time im using a PLL based on Imsmooth's circuit except i use the passive RC network rather than the opamp integrator.
Heres a video:
Experimentonomen, Sat Mar 19 2011, 09:27PM
Im back again and i have a new induction heater project.
This time im using a PLL based on Imsmooth's circuit except i use the passive RC network rather than the opamp integrator.
Heres a video:
Re: Induction Heater testing
IamSmooth, Sat Mar 19 2011, 10:32PM
Very nice.
What was that sound at the end? Water boiling in the coils? Are you using a coiling fan for the chips?
If you get the workpiece any hotter you are going to have molten metal (2400F melts, 5400F boils) falling on your platform. I would have some type of crucible with a water bath below the coil to catch the molten metal.
IamSmooth, Sat Mar 19 2011, 10:32PM
Very nice.
What was that sound at the end? Water boiling in the coils? Are you using a coiling fan for the chips?
If you get the workpiece any hotter you are going to have molten metal (2400F melts, 5400F boils) falling on your platform. I would have some type of crucible with a water bath below the coil to catch the molten metal.
Re: Induction Heater testing
Experimentonomen, Sun Mar 20 2011, 01:24AM
The sound at the end was steam returning to the coolant tank, pressurizing it and blowing out the vents.
I'm yet to find a cheap crucible that will withstand 1500deg C.
Heres a new video after a few changes:
Experimentonomen, Sun Mar 20 2011, 01:24AM
The sound at the end was steam returning to the coolant tank, pressurizing it and blowing out the vents.
I'm yet to find a cheap crucible that will withstand 1500deg C.
Heres a new video after a few changes:
Re: Induction Heater testing
James, Sun Mar 20 2011, 02:05AM
Pick up some refractory cement and make one. I don't know if it's called the same thing where you are, but here they sell it at hardware stores for repairing fireplaces and stuff. I saw some that said it could withstand 1750C.
James, Sun Mar 20 2011, 02:05AM
Experimentonomen wrote ...
The sound at the end was steam returning to the coolant tank, pressurizing it and blowing out the vents.
I'm yet to find a cheap crucible that will withstand 1500deg C.
Heres a new video after a few changes:
The sound at the end was steam returning to the coolant tank, pressurizing it and blowing out the vents.
I'm yet to find a cheap crucible that will withstand 1500deg C.
Heres a new video after a few changes:
Pick up some refractory cement and make one. I don't know if it's called the same thing where you are, but here they sell it at hardware stores for repairing fireplaces and stuff. I saw some that said it could withstand 1750C.
Re: Induction Heater testing
Experimentonomen, Sun Mar 20 2011, 09:34AM
problem is, thats only sold in like 50lbs bags or something like that.
Experimentonomen, Sun Mar 20 2011, 09:34AM
problem is, thats only sold in like 50lbs bags or something like that.
Re: Induction Heater testing
Experimentonomen, Sun Mar 20 2011, 12:14PM
Update:
Experimentonomen, Sun Mar 20 2011, 12:14PM
Update:
Re: Induction Heater testing
IamSmooth, Sun Mar 20 2011, 03:49PM
Go to Home Depot and buy furnace cement. It can withstand boiling metal. The problem is if you let the metal boil for too long you will melt the silica in the cement and get a metallic-glass mixture. However, for slightly lower temperatures, it is a good, cheap solution.
IamSmooth, Sun Mar 20 2011, 03:49PM
Go to Home Depot and buy furnace cement. It can withstand boiling metal. The problem is if you let the metal boil for too long you will melt the silica in the cement and get a metallic-glass mixture. However, for slightly lower temperatures, it is a good, cheap solution.
Re: Induction Heater testing
Inducktion, Sun Mar 20 2011, 05:16PM
Whats your schematic? You said you used Imsosmooth's PLL one right? Could you possibly elaborate on what you mean by RC passive network? Or draw up a schematic? Thanks ^^
Inducktion, Sun Mar 20 2011, 05:16PM
Experimentonomen wrote ...
Update:
Update:
Whats your schematic? You said you used Imsosmooth's PLL one right? Could you possibly elaborate on what you mean by RC passive network? Or draw up a schematic? Thanks ^^
Re: Induction Heater testing
Experimentonomen, Sun Mar 20 2011, 06:07PM
Imsmooth, only one problem, i don't like in USA so i don't have home depot here, my best bet is a cheap used silica clay crucible on ebay.
Inducktion: imsmooth used a integrator circuit between the phase comparator part ad the VCO input of the CD4046 pll if, i use just a resistor and a capacitor.
Experimentonomen, Sun Mar 20 2011, 06:07PM
Imsmooth, only one problem, i don't like in USA so i don't have home depot here, my best bet is a cheap used silica clay crucible on ebay.
Inducktion: imsmooth used a integrator circuit between the phase comparator part ad the VCO input of the CD4046 pll if, i use just a resistor and a capacitor.
Re: Induction Heater testing
James, Sun Mar 20 2011, 08:29PM
They sell it in small cans too, for making repairs. Look in the woodstove section.
James, Sun Mar 20 2011, 08:29PM
Experimentonomen wrote ...
problem is, thats only sold in like 50lbs bags or something like that.
problem is, thats only sold in like 50lbs bags or something like that.
They sell it in small cans too, for making repairs. Look in the woodstove section.
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