ZVS Induction Heater - 2kW

Thread Starter

kevinnas

Joined Jul 31, 2017
77
Hello.
I am trying to come up with a 2kW induction heater which uses the attached 48Vdc/3kW psu.
This is to be used with a water cooled copper coil. The circuit inductance is 3uH because the solenoid coil will have a 12cm diameter, 6cm length, and about 4-5 turns... and it will use a capacitor bank of 3 x 0.3uF MKP capacitors (1600Vdc) which gives a resonant frequency of about 100kHz.
I need the frequency to be high because this is to be used to heat up Iron micron sized particles to around +150 degrees
1. The problem is my PSU is 3kW and I have used 48Vdc with a series resistance of 0.8 ohm to simulate this but in the simulation the output without load is showing around 12kW peak initially and a steady 6kW output (which I do not know how it is possible if my power supply is only able to provide 3kW).
2. Will this initial peak be a problem?
3. Is it necessary to cascade the mosfets as I did or just using two beefy Fast switching mosfets can do the job?
4. Does this circuit seem okay or any improvements I can make?
5. The components chosen for the schematic are not fixed (Used because I had the models available in my library so if anything needs to be replaced I can do that).
6. I am currently also simulating with a load of 1mOhm series resistance but I do not know how accurately this models micron sized powder if anyone can also help with this?
 

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shortbus

Joined Sep 30, 2009
7,337
I'd say even though they sold the power supply as suitable for a ZVS, it's not. It looks like it is a switch mode supply, from every thing I read when making my ZVS induction heater they said not to use a SMPS. A linear supply is what people use, a transformer, rectifier and capacitor circuit.
 

Thread Starter

kevinnas

Joined Jul 31, 2017
77
I only want a 1.5kW-2kW induction heater and therefore the 3kW PSU should be more than enough?.
I believe the SMPS will be okay? a lot of youtube videos I have seen use these kind of psu and I am aware that for the Mosfets will blow up if the psu is not fast enough to turn on but I will use a circuit breaker/relay switch.
But before we even get to the actual build of the system, I am just not sure if my simulation is actually correct because I have an input 48Vdc with a series resistance of 0.8ohms which is aprox 3kW..and yet my simulation results are showing the circuit drawing 12kW..is that even possible?
 

shortbus

Joined Sep 30, 2009
7,337
I believe the SMPS will be okay? a lot of youtube videos I have seen use these kind of psu and I am aware that for the Mosfets will blow up if the psu is not fast enough to turn on but I will use a circuit breaker/relay switch.
That is why people using a ZVS induction circuit rely on a linear supply. If you pay attention to the Youtube videos, all of them having trouble and blowing mosfets are using a SMPS. There isn't enough"headroom"(think that's the correct term) to respond to the switching in the ZVS. But I'm not going to try to change your mind, but just ask you to look for your self on Youtube at all the failures with a SMPS.

This guy(link) has the best set of tests and has many working induction heaters. He is the one I ended up going with when making my own, since he already spent the money finding out what doesn't work and what does. It would be worth your time to read and watch all he has to say. Mine uses a 30V 625VA toroidal transformer and rectifier with caps.
https://spaco.org/Blacksmithing/ZVSInductionHeater/1000WattZVSInductionHeaterNotes.htm
 

Thread Starter

kevinnas

Joined Jul 31, 2017
77
That is why people using a ZVS induction circuit rely on a linear supply. If you pay attention to the Youtube videos, all of them having trouble and blowing mosfets are using a SMPS. There isn't enough"headroom"(think that's the correct term) to respond to the switching in the ZVS. But I'm not going to try to change your mind, but just ask you to look for your self on Youtube at all the failures with a SMPS.

This guy(link) has the best set of tests and has many working induction heaters. He is the one I ended up going with when making my own, since he already spent the money finding out what doesn't work and what does. It would be worth your time to read and watch all he has to say. Mine uses a 30V 625VA toroidal transformer and rectifier with caps.
https://spaco.org/Blacksmithing/ZVSInductionHeater/1000WattZVSInductionHeaterNotes.htm
Yes I have looked at his videos and notes, Thanks for the heads-up, I will definitely look into this if the power supply does not work.
Do you think the IRFP260N mosfets will be okay, since their VDS is only 200V and in my design using 48V means that I might be stressing them? Do you know of any alternatives that have good switching speeds too because my circuit will be running around 100kHz.. I read somewhere that said the Mosfets need to have a VDS at least (pi) 3.14 x the input voltage and I could use a mosfet rated much higher with good switching speeds and low RDSon but someone also mentioned that could cause problems because of the internal construction of the Mosfets they might not work above 200Vds?
 

Janis59

Joined Aug 21, 2017
968
1) I guess the initial "blow-up" happens because the resonant Tank is empty, thus the whole might of circuit tends to fill it up. When circulating energy in it stays high enough, then circuit is just supplementing an energy according how much is lost in the current cycle (and or heating).
2) ZVS/ZVT is VERY afraid about small load conditions near empty load. Then happens "hard switching". The same about hard overload near the short-circuit. Thus, I am not sure very much, this is the good application for ZVT/ZVS. Most of all it is simple modified Rogers oscillator in cheap apparatusses, or CD4046-based frequency-updated circuits in more professional circuits.
 

Petespaco

Joined Jan 9, 2020
2
I don't see anything wrong with using a Switched mode power supply (48 volts is best), as long as the one you choose can deliver at least 20 amperes without any voltage sag.
I use them on both my 1000 watt and on my 2500 watt systems. The only problem is that some Switched mode power supplies don't come up to full power for several seconds after they are turned ON. So----
- Install a DC power switch between the Switched mode power supply and the ZVS induction heater's DC input.
-Power up the Switched mode power supply and wait for 5 seconds or so.
-Close the switch to connect the power supply to the ZVS induction heater.
 
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