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Finished up ZVS need advice.

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brtaman

Sat Jun 20 2009, 07:44PM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Hello,

I just finished building a ZVS driver, my first, and I am amazed at the power, it is definitely a huge step up from my previous driver. I must admit I completly and utterly copied the design that Myke (I believe?) used on his perfect driver, sorry man it was too good to pass up, hope you don't mind.

Here are some specs:

4 wind Primary/ 4 wind Seconary
1.04 uF caps (seems to be my sweet spot and don't worry they are just dirty :P)
IRFP250N
Otherwise it is the ZVS circuit to the T.

After some time tuning it draws 6.2 amps peak at 12 volts, so 74,4VA input. My question to you experts is; is it possible to extract more out of the driver at this voltage? I am limited by the fact that my only source of DC power at the moment is a modified ATX PC PSU. It can handle 12V@15 amps, so as far as current is concerned I have quite some headroom, however it is the volt factor that is limiting me at the moment.

I would really appreciate advice on the output of the flyback.

(sorry couldn't get link to work, figured it out now)

My judgement: Arc ignites @ 13-15mm so in theory I would say it is around 12-14 kV?(no spheres) However this means that the current should be from 5.314 to 6.2 mA, which seems a bit high for a flyback in my uneducated opinion? Could you guys help me with this one, it is quite important as this flyback will be powering my SGTC v.2. and I need to calculate and buy caps for the MMC.

Zvsdriver

Thank you,
brtaman

Dr. Dark Current

Sat Jun 20 2009, 08:55PM

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

brtaman wrote ...

My judgement: Arc ignites @ 13-15mm so in theory I would say it is around 12-14 kV?(no spheres) However this means that the current should be from 5.314 to 6.2 mA, which seems a bit high for a flyback in my uneducated opinion? Could you guys help me with this one, it is quite important as this flyback will be powering my SGTC v.2. and I need to calculate and buy caps for the MMC.

This circuit draws mostly Watts, the VA oscillates between caps and the core. So I'd say it draws 74 Watts. If I remember correctly, someone said that this circuit needs "Q" of about 5 to work properly, so you might have ca. 350VA on the primary. With 12kV o/c voltage thats about 34mA short current.

As for increasing the power, you could use FETs with less ON resistance, 55V FETs will be enough, actually you dont want to go higher as the on resistance goes up rapidly with voltage.
Decrease the primary turns (possibly 3+3), use very thick wire to wind them, and increase the resonant cap value a bit.

brtaman

Sat Jun 20 2009, 09:03PM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Hey,

Thank you for your reply dr. Kilovolt, it is greatly appreciated.

I have stayed at 4turns for basically no reason now that I think of it...I think that 3 turns is a good idea. The thing is though, i would prefer a lower current and higher voltage (less caps to buy :P), you have any ideas? Less turns more V...? Seems logical?

The capacitance I have at the moment is the ideal capacitance for 4 turns going higher did not help, slightly decreased current draw. I suppose with 3 turns more capacitance should help quite a bit.

Are you sure about the 34mA though? That would make that power 420W!? 3.4mA?

What is your opinion on my output, based on the video?

Thank you,
brtaman

Proud Mary

Sat Jun 20 2009, 10:51PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Hiya, to get the peak voltage, why not just just rectify the output, and measure it across a capacitor?

brtaman

Sat Jun 20 2009, 11:14PM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Hey,

Pardon for asking, but what would this entail, I am quite interested in finding my output.

On a side not I am up to 8.2A :), three winds with added capacitance (thanks Dr. Kilovolt :)), driver is staying unbelievably cool though, guess that tiny vent is doing its job as the heatsink is on the small side.

So with 8.2A and 12v I am up to 98.4 W, not bad for 12v?

The thing is though, the arc looks less hot, it is more blueish than white when expanded, I haven't noticed a dramatically longer striking distance though?

Thank you,
brtaman

Proud Mary

Sat Jun 20 2009, 11:28PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

If you haven't got a single fast HV diode, you can string together a number of cheap fast rectifiers so the combined working voltage is well above your possible output voltage. Then connect this to a capacitor, and measure the peak voltage that appears across the capacitor.

You may also have to make a potential divider in order to read your output voltage off an ordinary multimeter.

I realise that this is not always so easy if you are just starting out, and don't have the components immediately to hand, but if you have to go and buy them it will only cost a few dollars, and will be well worth your while.

You're really operating in the dark if you don't have any basic means of making measurements.

brtaman

Sat Jun 20 2009, 11:45PM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Hey,

I have around 17 UF4007 diodes, they would suffice I think? Problem is that I am waiting for my PETP caps + MMC caps (have to order), so really no HV cap on me atm.

Thanks for the suggestion though, I will look into making the measurement asap.

What do you think of this design

? Seems ok

Thank you,
brtaman

Proud Mary

Sun Jun 21 2009, 12:04AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Vrrm for UF4007 is IkV, so if you don't want to stress them too much you can reckon on using them at 750V max each, or maybe just 600V when connected in a long series where the reverse voltage across each diode is not going to be precisely equal. So that would give you the ability to rectify about 10kV with a fair margin of safety using your 17 UF4007s. (ome forum members will work the diodes harder than this, but then be prepared for failures!

brtaman

Sun Jun 21 2009, 12:09AM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Hey,

Thanks for taking the time!

I am very tired at the moment and have a headache, so it is my opinion that HV testing will be suspended until tommorow. Will test the idea out and post my results.

thanks
brtaman

...

Sun Jun 21 2009, 06:12AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

As to your comment on sizing the MMC for your tesla coil, the normal methods of calculating the size for the capacitor would not work very well for this driver, because it is for the most part a constant power source. Your best bet is to pick a break rate (you can stick with 100hz, but 500hz would probably work with a decent spark gap and reduce the mmc size), and divide the input power by it to get the amount of energy you can supply per break, and get a mmc that big. Ex, for a 100w input and 100bps break rate you would want a 1j tank capacitor, so a 10kv 20nf capacitor would work well.

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