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First ZVS Driver / Induction Heater

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fatboyslim

Mon Feb 21 2011, 01:07PM

Registered Member #1779 Joined: Sat Oct 25 2008, 11:05AM
Location:
Posts: 32

Hi
I've been wanting to build one of these for so long, so two days ago i bought some MOSFETS and started to get to work. Unfortuneatly i live in New Zealand so finding IRFP250 were next to impossible, unless i bought them off ebay, but they would take a week to arrive, so i opted for some handy IRFP540's. I didn't follow the original design, and opted for a larger capacitor and dual inductor. It is powered by a 12v ATX powersupply. The sparks from this are quite impressive considering it is only 12v. The great thing is my MOSFETS and capacitors all remain cold.
Heres a vid of the ZVS Sparks: SPARKS!

I later modified the coil to be used as an induction heater
You can check out the vid here: Induction Heater

Do you know the best power source for this circuit? MOT are out the question. I tried using laptop battery chargers but they do not work as well as the atx. Is it fine to hook up more than one ATX PS together in series?

quicksilver

Mon Feb 21 2011, 03:18PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

In a sense you have a self imposed limitation - as the design was made for a high amperage source but the substitution of the MOSFETS (from the original 250's) demand that you stay within the confines of those that you are using. The datasheet

for your 540 will give you an idea as to the extent that you could climb from the feed of your ATX PSU but don't expect to much more. You could bring your voltage higher but your current must stay within reduced limitations. It appears that the "540" was designed as a 22A max device but your voltage could go quite a bit higher. However the Mazzelli was designed as a higher current driver. There is a possibility that the arc configuration itself would change (thinner blue?) at higher voltage. The only way to know, is to experiment; using the datasheet as a guide for alterations. You certainly can go much higher in voltage & the experimentation is the fun part!
As to power source; MOTs do not have to be used as the lethal little cubes that they appear. You could pull and replace the secondary and have a custom source. It's certainly not that difficult. You always need to remember that you have that 22A ceiling, but it would be very possible to rewind that secondary using a wire size source that places you in a higher voltage range but still maintain moderate current. It would be a unique project as you could record the various secondary to find just what yields the desired result. That information could be very valuable to future experimenters. The safety factor could be maintained in a variety of ways.
There simply aren't too many 20A sources to choose from that can give you up to 100v inexpensively. But there is an enormous amount of information on replacing the secondary's in a MOT and some of the results. extrapolating from that could give you an easy starting point.

James

Mon Feb 21 2011, 08:28PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

The power supply I use is nothing more than a 120V:50V transformer, rectifier and a filter capacitor that I plug into a Variac to get variable output. You can also modify an ATX power supply for higher voltage output if you want a compact switcher, or build something like this

fatboyslim

Mon Feb 21 2011, 10:02PM

Registered Member #1779 Joined: Sat Oct 25 2008, 11:05AM
Location:
Posts: 32

Thanks for the replies.
@quicksilver The IRF540n mosfet i am using has a max current of 33 amps, not 22A, Which is infact the same as the IRFP250. The only difference is the VDS and RDS.
@James That sounds pretty awesome. How many amps does your transformer put out, and did you have to change the resistor or zener values when you were running it that high?

James

Tue Feb 22 2011, 12:19AM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

I haven't really measured, it's just a cobbled together arrangement I'm using until I get around to finishing my big beefy bench supply. I think what I've got will do about 7A before the voltage starts to sag quite a bit.

I didn't modify the components at all. I'm using IRFP250s, 15V zener diodes and 2W resistors. The resistors are the only parts that get a bit hot, I think I'd use 3W parts if I were to build it again.

The voltage rating and RdsOn of the mosfets is probably more of a limiting factor than the current. I haven't had a chance to scope mine yet but I recall the voltage across the mosfets is close to 3x the input. If you're stuck with a lower voltage, you ought to be able to decrease the number of primary turns to compensate up to a point.

haxor5354

Tue Feb 22 2011, 11:50PM

Registered Member #2063 Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352

I wouldn't recommend holding the HV wire from a FBT with just your bare hands :\

you could try using lead acid batteries, just make sure your circuit is fuse protected. your fets might explode if you did something wrong by accident. connecting ATX PSU is series will just short circuit, because the negative terminal (black wires) are connected to ground.

fatboyslim

Wed Feb 23 2011, 01:34AM

Registered Member #1779 Joined: Sat Oct 25 2008, 11:05AM
Location:
Posts: 32

@ Haxor5354. Thankfully noted. Will attach it to a wooden pole next time.
As about the ATX psu's i was intending multiple psu's, not just one

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