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Sparkie

Wed May 02 2007, 02:47PM

Registered Member #627 Joined: Thu Apr 05 2007, 04:05PM
Location: London
Posts: 32

Hello everyone! I have just built my first ZVS flyback driver, and it works lovely! I have a question..

Why is it when I up the voltage, I get smaller arcs? Would I need more turns on my primary? Currently using 5+5. It could be that my 24v PSU hasnt got the power, unless theres another reason.

Anyway, heres a pic, and a video of my first tests with this driver. The heatsink doesn't even get warm, guess I didn't need one quite this big!! Only thing that gets warm is the 680nF Capacitor.

Thanks! John.

http://youtube.com/watch?v=ZjJzt8EBokc

zvs_driver_new.jpg

zvs_flyback_windings.jpg

zvs_setup.jpg

uzzors2k

Wed May 02 2007, 03:13PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Looks good, nice and clean. Remove the insulation next time before arcing!

What frequnecy is it operating at? 5+5 is a bit low for 24V and 30-50kHz?, my guess is that your core is saturating. Try 15+15 turns with thicker wire, and cut down from there until you get the best arcs. The arcs look about right for 24V in though.

Sparkie

Wed May 02 2007, 03:39PM

Registered Member #627 Joined: Thu Apr 05 2007, 04:05PM
Location: London
Posts: 32

Hi Uzzors, thanks for the reply. What insulation do you mean? The video is with a 14v input, just when I try 24 the arc is real thin and weak. It could be my PSU but I dont think so. Im going to build a 25 ish volt psu from a 22v toroidal transformer I have.

As for frequency, it runs at 42KHz with no arc, and 54KHz while arcing.

I just updated the video with another clip on the end. When pulling the arc, it goes from firey hot glowing arc, to thin purple arc just before it extinguishes. Wonder what causes this? You can see me play with it, and hear the PSU buzz when its large, just before it goes purple and thin. It draws around 3.5A at full length arc. Is it that at 24v it needs more turns, because it will oscillate at the wrong frequency with 5+5 ?

Anyway its all good fun!!

[EDIT] OK just tested the frequency at 24v with 5+5, its 84KHz no arc, and 110KHz while arcing!! So I take it thats my problem, and that I need about 10+10 turns to get down to <50KHz?

http://youtube.com/watch?v=ZjJzt8EBokc

uzzors2k

Wed May 02 2007, 05:48PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

I meant the return wire insulation, which was releasing magic smoke.

Yeah more turns increases the primary inductance, which brings the frequency down closer to what the flyback likes. Higher frequency lets you get away with fewer turns though, so its a trade off. Higher frequency = higher voltage and long thin arcs, lower frequency = low voltage and power arcs. Funny that the frequency increases as the voltage increases, I thought the Mazzilli ZVS driver was a LC circuit, which is voltage independent. Are you measuring the frequency at one of the mosfet bases? If not do so. The " Mazzilli ZVS Driver driven from more than 40V (how many times has this come up?)" thread just two threads under this one is pretty relevant for you, since my 50V PSU sunk to 20-30V under load. There Sulaiman gives a formula for primary turns needed on a ZVS type driver. Check it out.

However by the looks of your arcs I think the power supply can't provide enough current. Have you measured the voltage when pulling an arc, and is the supply current limited?

Sparkie

Thu May 03 2007, 05:12PM

Registered Member #627 Joined: Thu Apr 05 2007, 04:05PM
Location: London
Posts: 32

Cheers. The PSU is fine, I wound a new primary of 10+10 and it runs about 55KHz at 24v, and gives good results. I notice now the actual flyback starts to get warm, so I guess it wont take much of this. Is 55KHz a bit high still? Looks like its working fine, might try 12+12 see what difference that makes.

Anyway, heres a vid at 24v for now :) ZVS_Driver_24v.wmv

uzzors2k

Fri May 04 2007, 04:50PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

The arcs look better now.

Sulaiman's formula will find the minimum amount of turns, which is just what you want to use. More turns actually cut down the voltage, but are required to prevent saturation. Also the inductance of the primary increases with each turn added, so the frequency decreases. So just experiment to find what works best.

When it comes to frequency, it depends on voltage and how many primary turns you can fit on the core. When I run my flybacks offline I use 100kHz, and when I run them from 12V I drop the frequency to 25kHz. They give more firey arcs at low frequencies, since they have their own resonant frequency, and they're designed to work at low frequencies. If you can fit the turns in, drop the frequency. (larger resonant cap. and more primary turns)

Sparkie

Mon Jun 04 2007, 08:12PM

Registered Member #627 Joined: Thu Apr 05 2007, 04:05PM
Location: London
Posts: 32

Thanks! Just adding a video of a new AC flyback I found in a dumped telly. I was expecting more from this really. It seems to be high current but low voltage. Arc starts about 3mm but is flaming! The resistance over the secondary is 368ohm. The output went into a rectangular component about 10cm long then out of that into the plunger on the tube. I imagine this is the rectifier? Or could it be something to up the voltage? I might go and get it, see what it is.

Anyway, all good learning... heres the vid: Small_AC_Flyback.wmv

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