Chinese Ebay Royer induction heater tests

[RocketScienceSmurf]

I received two similar ebay induction heaters a few weeks back that I will use for further tests and measurements before I put my own together. You can see from the pictures that they look alike but there are some small differences. The one on the left uses a much larger area of the pcb to conduct the power, whereas the one on the right relies on extra solder instead. I think the left will perform the best.

I also attached a small picture of the zener diodes I will be using on my own IH. It's a Russian 8W 15V zener diode. I will do some experiments as soon as I have my power supply up and runnig.

[Mads Barnkob]

It is really hard to make out the outline of the PCB tracks, could you take a picture of it from a slight angle?

There is fatal flaw in their routing of the tracks, the MKP capacitors that make up the resonant tank capacitor are not connected for even current distribution among the capacitors. The capacitor closest to the work coil connectors will over heat before the one furthest away will even see a load near its rating.

You should cut the PCB traces and rewire it to help the capacitors live longer

http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/dc-bus-capacitor/

While ripple current divides among the capacitors in proportion to capacitance values for low-frequency ripple, high frequency ripple current divides in inverse proportion to ESR values and path resistance. [2]

This means that parallel capacitors in applications with low frequency load will share the current according to the capacitance of each capacitor in parallel. Whereas a load operating at a high frequency, like a DRSSTC does, the current sharing is up to ESR values and resistance of the busbar and wires in the circuit.

[RocketScienceSmurf]

This is about as good a picture as I can get from my mobile phone.

I am fully aware that both boards are less than optimal when it comes to the tank capacitors but these two boards are just for further testing and I don't care if the caps or mosfets blow up as long as I can learn anything from it. I am thinking about buying an 8 channel USB oscilloscope so I can measure a lot of signals at once. They can be had pretty cheap on ebay, but I have already bought a few quite pricey instruments for this project.

[afk]

Hmm... So the capacitors on the board are actually capacitors used in induction stove. I just bought some myself (20 of them for around $5! Same brand BM cap from China) and they looks functional.

[RocketScienceSmurf]

Hmm... So the capacitors on the board are actually capacitors used in induction stove

Yes and no. BM has several different types of "induction capacitors" but the ones I think you are interested in are the ones used in the tank circuit. Those are usually around 0.33uF and rated for 1200V.

[afk]

Hmm... So the capacitors on the board are actually capacitors used in induction stove

Yes and no. BM has several different types of "induction capacitors" but the ones I think you are interested in are the ones used in the tank circuit. Those are usually around 0.33uF and rated for 1200V.

I got MKP-X2 ones, though.

[RocketScienceSmurf]

MKP-X2-series capacitors probably wont survive long in a tank circuit. They are not specifically made to handle the high frequency/high current usually present in that kind of application. You want the MKPH-series.

http://en.bm-cap.com/productview.aspx?id=21

[Mads Barnkob]

The very wide PCB tracks explains why I could not see them, they make up half the board

Most MKP (polypropylene) capacitors can be used/abused in a resonant circuit, it is only a matter of their reduced life time.

X2 capacitors are safety capacitors meant for use in input filtering and are rated for high transient voltages, properly not so good on the current side of things. Often you can not even find the current rating for these capacitors, but I suspect that is only because the manufacturers do not want these cheap capacitors used in applications where they could normally sell much more expensive capacitors.

Did any of you play around with my MMC calculator? It was made for Tesla coils, but works just a good for calculating induction heater tank capacitor: http://kaizerpowerelectronics.dk/calculators/mmc-calculator/