IsoTop ZVS driver.

Chris Cristini, Tue Jan 26 2016, 05:58AM

Hi its been a while but i have a project at work I would like to share It is a ZVS Induction heat treat machine for Injection molding ejector pins I am using a HV Transformer for testing and have been abusing the heck out of it but with only 12V@29A about 350W i am waiting for a 1000W 48V SMPS it should be here in a few days from Mouser. I am using a pair of STE88N65M5.

ProtoTrak CNC machine used.

Video.



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Re: IsoTop ZVS driver.
Chris Cristini, Thu Jan 28 2016, 05:09PM

Sorry for all of these posts in a row. hoping for that PSU today we will see. I am getting good practice with the CNC machine.

Of course some of it is Ugly but I am test fitting everything before I get in to finishing touches after this is done i will start building the small stand with a Ball screw actuator for the work piece I am planning on building a cover that seals the work piece in an inert gas environment just for case hardening.

Also when the work piece reaches the curie point I remove some Capacitors raising the frequency and the part actually rises in temperature now my knowledge with heat treating is nominal at best should I stay below or above the curie point?

Re: IsoTop ZVS driver.
Kizmo, Thu Jan 28 2016, 05:16PM

This looks so nice! As machinist stuff like this really warms my mind

Re: IsoTop ZVS driver.
Chris Cristini, Thu Jan 28 2016, 06:15PM

Thank you so much!! You have no idea how much that means to me aside from the 2 axis CNC plasma table I built in 2010 I have very little experience programming but it's my job now :)

update I received the big smps and it worked great however a 1/4" pin glowed red in seconds at 23.6 KHz but then the litz wire primary smoked then shorted what should I use that will handle a kilowatt?

I was also curious of how large of an arc I could draw it was a good one but a few sparks jumped from the source to gate I was sure I cooked a $30 FET but it was unharmed I would recommend these Mosfets to who ever wants to make a ZVS with Isotops cant go wrong with .029 Ohms better than IRF250.

A video of the terminals I used glowing red


More pictures

Re: IsoTop ZVS driver.
Inducktion, Fri Jan 29 2016, 08:12AM

Well! The terminals are almost certainly glowing red from poor connectivity (look how little of the connector was actually touching your work coil). Because of that you get ridiculous resistive losses, and a lot of heat.

Additionally, if your frequency is indeed 23.6 kHz, then you don't really need litz wire. The skin effect is nil at that frequency and you'll get much much much better results with thicker regular wire.

A quick reading of the datasheet for that fet... 8.8 nF of gate capacitance! That definitely isn't a small FET. You may get better results if you lower the gate /resistance/ a little, since it'll allow more current to flow to the gate. Not a whole lot lower, just a little, like 330 ohms or something.

Re: IsoTop ZVS driver.
Chris Cristini, Fri Jan 29 2016, 02:41PM

Yea I always seem to overlook small obvious things :) I actually thought the glowing connector was kind of cool but not the purpose I rewound the transformer with normal 4GA and certainly works far better and allows for even more current 5+5 Pri 5 Sec.

Thank you Inducktion I am considering maybe paralleling two 470s for 235 but may be too low ill see.

The company I work for likes everything over built I think I am fulfilling there wish with this another thing is it is nice that I am automation maintenance so have nothing to really do when I keep everything running so nicely and nothing is down.

Re: IsoTop ZVS driver.
Wolfram, Fri Jan 29 2016, 03:05PM


This is not true. The skin effect is present at all frequencies, and at 23.5 kHz the skin depth in copper is less than 1.5 mm. With 4 AWG wire, there is already a significant difference between the AC and DC resistance. This applies for a straight wire, in a transformer it will be significantly worse due to the proximity effect, so litz wire makes sense. As long as you have some of proper cross section of course.

Re: IsoTop ZVS driver.
Chris Cristini, Fri Jan 29 2016, 07:25PM

I am considering a new transformer design about Half the size as the one I am using and thinking of a water cooled Secondary?

Re: IsoTop ZVS driver.
Sigurthr, Fri Jan 29 2016, 08:40PM

8.8nF really isn't bad for gates at such a low frequency. In some of my TCs I'm driving the 12nF gates of my FDL100N50F's at close to 1MHz. Granted, peak gate currents are higher due to much lower gate resistance in my circuit. If gate rise/fall time is slow I'd probably change out the resistors, not the FETs.

Litz always helps, it's just a question of if it helps enough to justify the cost.

Re: IsoTop ZVS driver.
Chris Cristini, Sat Jan 30 2016, 05:41AM

I actually managed a long run at 48V and held right on to one of the fets and they stay completely cool not even the slightest bit of heat also the resistors stay cool too so i may just leave it traditional to the original schematic found on google images. I am happy with it and again you guys should try those Mosfets they are great and Robust I have not yet latched one and even had HV spikes jumping over traces on the Gate Circuit all though that may be what saved them shorting to ground before destruction.

Re: IsoTop ZVS driver.
hen918, Sat Jan 30 2016, 02:48PM

What are the TO-220 packaged components in the pictures? Diodes?

Re: IsoTop ZVS driver.
Chris Cristini, Sat Jan 30 2016, 03:04PM

Yep they are Ultra fast.

Re: IsoTop ZVS driver.
Chris Cristini, Tue Feb 02 2016, 05:45AM

I was able to replace the small terminals with 0.2X0.5X1.75" copper buss bars that I milled out of a chunk of copper they work allot better but I still have a smoking transformer.

Under load it switches @17KHz +- .35 In the video it gets a 5/8" ejector pin to glow in about 30 Seconds which is a bit fast but it will have to heat a 1" ejector pin anything bigger goes some where elts.

Re: IsoTop ZVS driver.
hen918, Tue Feb 02 2016, 08:52PM

Try decreasing your tank capacitance (to increase frequency) and using less, thicker, turns on the primary and secondary. This will give you less resistance in the windings, at the expense of a larger magnetic flux going through the core. My guess is that the core isn't the heat generating one here and the windings are smoking. If the core is itself overheating, you need a bigger transformer.