Induction Heater ZVS Problem - Page 1
Forum section: electronics / general

author: Teknow
author_rank: Regular Contributor
timestamp: November 16, 2022, 06:49:10 pm
content: Hi everyone!Years ago I built the ZVS induction heater almost known for all induction heating enthusiasts and now sold almost every where in the net, like this onehttps://www.open-electronics.org/wp-content/uploads/2017/08/1298_Schema.png,but without R1, LED and C7.My problem is, once I insert a thick metal object 10mm thick or even 8mm for instance along the coil and once the current drawn exceeds 10 Amps the circuit stops resonating and it draws full current from the power supply >30 Amps.I built another circuit and I made the heat sink chasis minus. I thought there might be some oscillation or so, but I still get the problem. I used different power supplies, changed the diodes, capacitors, and the coils, but nothing has changed. I see videos in the YouTube where people use the same circuit and similar components and they heat wrenches, iron bars, etc. where the coil is round the middle of the object not only the tip or the first 30 mm of it. One of my circuits uses 4 IRFP450, the other 2X 20N60C. The first circuit is powered from an SMPS 18 Volts 30 Amps and I use 7812 connected with two 150 ohms resistors to drive the gates. The one that is powered by 12 volts has no Zener diodes at the Gates.I wonder why am I having trouble while all the Youtubers get their circuits to work properly! I appreciate help.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 16, 2022, 07:41:25 pm
content: Quenching oscillation means there's not enough gain to counter the loss in the tank. Try a lower frequency (more capacitance)? Larger dia coil?Also be sure that your supply inductors aren't saturating too badly under load current. They're probably big enough but it would be good to know.Tim

author: Teknow
author_rank: Regular Contributor
timestamp: November 16, 2022, 08:37:21 pm
content: Thanks T3sl4co1l, I've already tried more capacitance and inductance but the power consumption without metal inside rises, current is 5 Amps on idle. I tried lower capacitance 1.1 uF, 2.5 amps on idle, less current but the same problem. I use UF4006 diodes and not UF4007. For the double Mosfet version I use BYV29F 500. I wonder if these too matter??!!I inserted an iron bar and turned the thing on it went to 20 Amps then up to more than 30 Amps and finally short circuit. I have to check the Mosfets.One Mosfet was blown out.I repaired the circuit (12 Volts version no Zener diodes) and I added a BC501 8 A Hosiden protection breaker, it shuts off once the current exceeds 8 amps.Searching in the internet, I came across this site:https://spaco.org/Blacksmithing/ZVSInductionHeater/1000WattZVSInductionHeaterNotes.htmwhere I could conclude from an indirect reference to the problem.1. If the supply voltage drops down to less than 11 volts the oscillator stops oscillating, and2. the ZVS has limits it switches off (no oscillation) once the coil is overloaded with thick metal. I haven't found people elaborating and pointing out this issue.I thought one can use the module to heat up from needle to >1 inch bars or more etc while only the current consumption rises.But that's not the case as I understand. I used 17 volts (24 Volts version 7812 regulator instead of Zener diods) and a 10 Am breaker. The voltage dropped down to 16.6 volts only. The power supply flickers (I hear clicking when approaching 11 Amps). There was continous on and off from the power supply without the current meter moving full 50 Amp scale.