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Critical ZVS Malfunction

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Juniortore1

Tue Aug 02 2011, 11:37PM

Registered Member #4014 Joined: Wed Jul 20 2011, 05:31PM
Location: SE Michigan
Posts: 25

Hmmm, why did my ZVS here stop working?

Well, I was arcing at 59v input (drops to 38v) when the output stopped and my transformer hummed.

Specifications then:
*IRFP260N
*1n4744a zener diodes
*10k 1/4W resistors
*470 Ohm 2W resistors
*.60uF 400V capacitor bank
*1n4007 "fast" diodes

The driver looks like this

After being depressed from my end of fun as usual, I unhooked the driver and then found something very interesting:

Do you happen to see what I am seeing there in the middle? That was at one point a 1n4007. Remembering before I disconnected the power after the driver died, I saw one of my zeners flash a few times.

So, after all of that fun, I replaced the 1n4007's to MR852. I also replaced the zeners and the 10k resistors to 1/2W even though there was nothing wrong with the resistors in the first place.

The 470 ohm resistors were replaced with two new 470 ohm resistors in series for about 1100Ohms (metered) so that they wouldnt get as hot and loose their color over time. That also allows more power to the driver (60-70v with single PSU input)

After more arcing, my .68uF caps came in the mail. I threw one on and saw more power output (the mosfets heat a lot more though). So I kept it, just for it to turn into this after:

Problem?
U Mad capfags?

So, hopefully that is all that blew after the capacitor replacement was the capacitor. I will switch it back to .60uF and keep all of my other .68uF ones to make a bank for my higher power ZVS I am making. Lets hope the fets didnt die this time after another fail, they seem to be pretty durable with all of this crap happening.

Since you are here, if you want there are some lame ZVS videos on youtube. Ill have to edit and upload more.

Adam Munich

Wed Aug 03 2011, 03:25AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Since the zvs is a resonant circuit the current circulating in the LC tank can be many times the input current. Say your zvs is drawing 5A, well the LC tank current could very well be 30A! Most caps don't like that...

haxor5354

Wed Aug 03 2011, 03:36AM

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

is that a poly film cap that I see there?
use better caps

Herr Zapp

Wed Aug 03 2011, 05:27AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Junior -

Are your .68uF capacitors metallized film, or film/foil construction?

The failure mode shown in your photo, where the metallization at the ends of the capacitor roll (where the leads are attached) is burned away, is typical of an over-current failure. With a metallized-film construction, the electrical connection between the sprayed zinc metallization and the edges of the metallized film is very susceptable to failure from excessive current.

You need to switch to capacitors with film/foil construction, and/or add more capacitors in series/parallel strings to increase the current carrying capability while maintaining the correct capacitance value.

Herr Zapp

Dr. Dark Current

Wed Aug 03 2011, 08:53AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

I use MKP X2 caps in this circuit, they are free from circuit boards and usually don't heat up.

Marko

Wed Aug 03 2011, 12:02PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hello,

The 1n4007 diodes are doomed to fail from recovery losses in this circuit, especially at such high input voltage. I'm surprised that they even lasted that much; UF4007's are in order there. If you want to run with 70V in you should probably consider a separate power supply for gates too.

Another note, those chinese brown drop caps are quite useless, even while they are polypropylene they seem to be inferior to WIMA or other quality brand caps.

I'm also surprised how much you guys tend to push this circuit with just one cap in the resonant network. It's not as demanding as an induction heater in matter of reactive power to drive a flyback, but I'd still use like 5 parallel caps for those power levels!

Now one thing I'm curious about, what kind of (flyback?)transformer do you drive with that monster royer oscillator so that it lives?

Marko

Newton Brawn

Wed Aug 03 2011, 12:37PM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Juniortore1:

Hmmm, why did my ZVS here stop working?

Well, I was arcing at 59v input (drops to 38v) when the output stopped and my transformer hummed.

Specifications then:
*IRFP260N
*1n4744a zener diodes
*10k 1/4W resistors
*470 Ohm 2W resistors
*.60uF 400V capacitor bank
*1n4007 "fast" diodes

Do you mind to provide a sketch of the electrical schematic and detail of the caps, as well as the transfomer(s) winding data ?

Regards

Newton

Juniortore1

Wed Aug 03 2011, 07:23PM

Registered Member #4014 Joined: Wed Jul 20 2011, 05:31PM
Location: SE Michigan
Posts: 25

@EVERYBODY: I will try to make a video showing the details of the driver.

@Herr Zapp: The capacitors are CBB Metallized Film Capacitors. I tried one just to see how it would last. At first, the results were great, little heating on it, until it just cracked without warning.

@Marko: The 1n4007's worked for 4 days worth of arcing at 59v (idle) and 38V when drawing huge arcs. I was honestly amazed how long they lasted!

I have already killed one large rear projection screen TV flyback. It got so hot that the plastic chipped off the inner epoxy. Then the rectifier diode blew, and it drew fatter arcs, then the epoxy went from white to a brownish. And then, it just stopped arcing.

Well, I am back to my film capacitor bank of 2x 1uF 400V capacitors in series. They get hot, but if they lasted this many days, I think they will last forever as I cant really push more power through these traces.

I will try the brown chinese film caps with a series parallel configuration on my friends ZVS driver I am making him.

@Newton Brawn: Killa-X made this PCB for me, I have never designed a PCB as I do not have the materials to do so. Anyhow, I will make a video showing front and back of the PCB. It is really simple.
------------------------------------------ -------------

But first before I make that video, I will upload a video I just made of some huge arcs I get through this green ink dot flyback. Poor thing :D

Juniortore1

Wed Aug 03 2011, 08:55PM

Registered Member #4014 Joined: Wed Jul 20 2011, 05:31PM
Location: SE Michigan
Posts: 25

Heres my newest ZVS video

haxor5354

Wed Aug 03 2011, 09:54PM

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

the flyback is arcing to your table!!! are you sure thats a good idea?

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