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two part question regarding zvs mazzelli and a custom pwm driver

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genoober

Tue Oct 25 2011, 03:11PM

Registered Member #4055 Joined: Tue Aug 16 2011, 06:56AM
Location:
Posts: 8

I know this should be two posts. But they both have something in common.

I keep blowing the mosfets in my zvs driver. Yes the irfp260's are heat sinked. I have double and tripple checked the schematic. I can't seem to find anything wrong and I get no arcs/sparks from my flyback (pulled from a 20 inch dell monitor). I've killed 6 mosfets, and I am getting frustrated.

I also have a pwm driver built from picaxe08m mcu pushing a irl2910 mosfet. The duty cycle is 80% and the frequency is variable. I get some very small arcs from this (5mm to 7mm). I have audio modulate those small arcs the clasic "legend of zelda" theme song.

Now here is the big question that relates to both problems. Could the problem lie in my power supply?

My "lab" power supply is a converted 580 watt pc psu. 12v rail is rated for 38amps and 5v rail for 57 amps

And yes I feed the zvs and pwm with a larger gaugue wire than what is in the psu now.

Inducktion

Tue Oct 25 2011, 04:03PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

When I saw your protoboard with the ZVS driver on it, I first thought "It looks nice". But, I did notice that the diodes don't ...look like zener diodes. Are you sure you used 12 - 18 volt zener diodes? Also, it seems like the mosfet closest to the picture (in picture 1) doesn't have a positive wire to it's gate... (you may have soldered it under the board, though) And, your inductor looks like it's wound on ferrite. If you use powdered iron cores (the yellow ones, or sometimes green ones) you find in ATX supplies and wind around 20-30 turns on it, it should work better. (that's from personal experience anyway!)

Another thing, is that it's generally a good idea to keep your semiconductors on a heatsink, especially when first plugging something in. It (usually!) keeps mosfets from blowing up/melting if something isn't working right, by taking the heat away, where if your mosfets are bare, the heat has no where to go, and thus, dead mosfets.

You will also get considerably louder/longer/hotter arcs for both of your projects there if you upgrade to 24 volts. ^^

I also like your keyboard. It's the same one as mine. :)

genoober

Tue Oct 25 2011, 05:13PM

Registered Member #4055 Joined: Tue Aug 16 2011, 06:56AM
Location:
Posts: 8

I've checked the inductor against an lcr meter and it reads .47uh.
The diodes that don't look like actualy are. 5w 12 zeners. I was thinking maybe that I was being an idiot and forgot the anode cathode legs were which.

I've been playing with mcu's for a while and forgot most of what I learned about discretes... the voltage monkey is back on my back after allmost 10 years without a hobby
Wahoo

Anyways
First pic is old heat sink that was used on that board. Second pic is new heatsink

Third is the underside of the veroboard on the zvs

1319562805 4055 FT126888 Img 20111025 101155

1319562805 4055 FT126888 Img 20111025 101203

1319562805 4055 FT126888 Img 20111025 101217

genoober

Tue Oct 25 2011, 05:28PM

Registered Member #4055 Joined: Tue Aug 16 2011, 06:56AM
Location:
Posts: 8

Also does anybody know how durable/safe it is to set up two pc power supplys in series to obtain 24v? I've googled but can't find much on running pc psu's in series.

I've heard of people stacking them in parrellell for high current. Sorry about the spelling my cellphone doesn't have a spell check.

Inducktion

Tue Oct 25 2011, 06:12PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

I believe they don't work in series; something about fighting to maintain regulation and thus losing regulation all together...

And, if your inductor is really .47 uH, then it's no wonder it's not working!

Try to aim for much much higher inductance. .47 uH is WAY to low.

teravolt

Tue Oct 25 2011, 07:26PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

you will have to find a 24v 8A or so transformer and make a raw DC power supply consisting of a bridge rect. and large filter cap. it is more beefy than that computer supply.

Newton Brawn

Wed Nov 02 2011, 02:34AM

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

Hi Genober !

The inductor shall have inductance enough to allows the semiconductors comutate properly
Inductances in the range of 20 to 200 uH are usual
0.47 uH not good ( Or your measurement has a mistake)

My experience with ferrite inductors in ZVS are not good, allawys the inductor core saturates and the inductance is reduced too much, heathing the semiconductors.

But it is very easy to solve this problem with a testing solenoide
Wind AIR CORE core test inductance
50mm (2 inch) diameter
50mm (2inch) lenght
54 turns wire 1mm diameter (#18 AWG)
ad you will get 100uH.

If you provide a tap on the 27th turnd you can get 38 uH

and a tap on the 40th will provide 65uh

All values check your meter.

this inductor can be used to optimize your ZVS

Regards

buxtronix

Wed Nov 02 2011, 05:52AM

Registered Member #4078 Joined: Tue Aug 30 2011, 12:53PM
Location: Sydney, Australia
Posts: 19

What are your fast rectifiers? If they are rated to 200v or less, they could be the problem (I killed a ZVS this way).

Antonio

Wed Nov 02 2011, 11:45AM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

The series inductor is quite too small. Its inductance shall be greater than the inductances of the flyback primary coils. This oscillator is not very safe. It will self-destruct if the series inductor is too small, if the core of the series inductor saturates, or if too low impedance is connected to the output.

teravolt

Thu Nov 03 2011, 01:35AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

load your core with as many turns as you can. I think you have a wiring erorr or your capacitor is the wrong type

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