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My first ZVS

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Whiplash

Thu Apr 04 2013, 12:23PM

Registered Member #11363 Joined: Mon Mar 18 2013, 04:29PM
Location: Brazil
Posts: 19

ok, on arc of 3cm to 5cm it start to drawn at 9A and goes to 15,6A until the arc stay.
I will try to buy IRFP260, they are better and bigger :D

Kiwihvguy

Fri Apr 05 2013, 11:34AM

Registered Member #3395 Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193

Ok thanks for the measurements. From the datasheet of the IRF3205, the ON resistance is 8 milliohms or 0.008 ohms and if the maximum current the ZVS draws is 15,6 amps, then: the fets will dissipate 1.9 watts of heat so this is not a problem since they are rated for 200 watts.

I would make sure that your heatsink is big enough and you use some thermal greases to help the heat transfer from the fet to the heatsink.

I agree - the IRFP260 sounds like a good idea!

But the heating will build up on the heatsink over time - especially for 5 minutes like you said. Whiplash - the last time the fets blew/overheated, were they hot?

Whiplash

Fri Apr 05 2013, 07:09PM

Registered Member #11363 Joined: Mon Mar 18 2013, 04:29PM
Location: Brazil
Posts: 19

Jozef, they blowup in just 1 sec or sometimes they blow in 2 or 3 min of hard work ahhaha, i use an small heatsink but have a 60x60mm 12v fan.
I think, the primary winding are too small, and the fets blow.
One question, i can use the primary original on the flyback? For 555 drivers i can.. and for ZVS will work?

Kiwihvguy

Sat Apr 06 2013, 03:37AM

Registered Member #3395 Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193

I think they might be blowing because of a voltage spike. After all, they are only rated at 55v and especially with mains-run transformers, voltage spikes can happen from time to time. I agree the IRFP260s are a good idea because they are rated at 200v, so if you do have a voltage spike it so much less likely to go pop.

How big is your primary? From my understanding it's usually 5+5 turns.

You can use the original primary built in the transformer for a 555 driver but it won't work for the ZVS because it requires two coils with centertap essentially.

In both cases you are much better off just winding your own primary because you have much more control over how many windings there are and it's still incredibly efficient. A lot more practical than trying to find the original primary coil embedded in epoxy among 10 other different ones haha...

Whiplash

Sat Apr 06 2013, 03:00PM

Registered Member #11363 Joined: Mon Mar 18 2013, 04:29PM
Location: Brazil
Posts: 19

True, its some hard to find on a stor the IRFP260/250s. >.<, one question, about the primary, if i increase (something like 10+10) the turns, less voltage output and more amperage right? And a big cap = less frequency.

Kiwihvguy

Sat Apr 06 2013, 11:11PM

Registered Member #3395 Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193

Ebay by far is the best place for hard to get fets/igbts
This is a good deal for you: http://www.ebay.com/itm/IRFP260-N-NEW-POWER- MOSFET-BY-IR-LOT-20-OF-/380592247833? pt=LH_DefaultDomain_0&hash=item589d10d419

You should buy way more than you need because it's guaranteed one or more of them will blow unfortunately.

Increasing the turns on the primary will decrease the voltage output but it won't increase the current. If you want more current, use a decent flyback and a beefy power supply. Correct, higher capacitance will decrease the operating frequency but I think it's more important that the capacitor is built to withstand the high currents sloshing around in it, like an MMC (2 parallel, 2 series etc).

Whiplash

Sat Apr 06 2013, 11:43PM

Registered Member #11363 Joined: Mon Mar 18 2013, 04:29PM
Location: Brazil
Posts: 19

Good, thanks for the answers, i will do more tests now, with that poor irf3205 and i get an old 2SC5297, but its a BJT =/. i will try news turns on primary, maybe i can make my fets last longer :)
Already, thanks again.

Kiwihvguy

Sun Apr 07 2013, 12:03PM

Registered Member #3395 Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193

Not a problem. Glad to help

I don't think using that BJT will improve at all because it's only rated for 8 amps continuous according to the datasheet

Bets will be it'll pop right away especially when you're cranking arcs and drawing over 10 amps! Not to mention also it's fall time is 0.2us (200ns) so it's probably too slow anyway and this will cause lots of losses in heating, leading to failure.

You don't need to put new turns on the primary unless you are going to substantially increase the input voltage.

Let me know how your testing and improvements go!

Whiplash

Mon May 06 2013, 06:57PM

Registered Member #11363 Joined: Mon Mar 18 2013, 04:29PM
Location: Brazil
Posts: 19

20x IRFP260's are comming xD

Kiwihvguy

Mon May 06 2013, 07:12PM

Registered Member #3395 Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193

Good one, I see you foresaw what was going to happen. Them MOSFETs will blow eh!

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