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ZVS flyback driver voltage and power questions

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Adrian

Sun May 20 2007, 04:10PM

Registered Member #697 Joined: Thu May 10 2007, 12:28PM
Location: Australia
Posts: 22

Hi, I've constructed the ZVC flyback driver circuit from the hvwiki. For me this was a relatively ambitious 'project' (if you consider a few hours work to be a project) being far higher powered than anything I've made so far.

It uses two IRF540N mosfets and is powered by the +12v rail of a computer PSU (10A).

Running it at the minimum recommended voltage certainly seems to make the output suffer. Arcs start at 1-2mm and can be drawn to about 1 inch max. However the arcs are of course, incredibly hot and quickly melts/vapourizes any electrode less than 1mm thick.

Will doubling the input voltage roughly double the output voltage and thus distance I can draw arcs on the output?

Could anyone recommend a good way to power this circuit at more than 12v. I tried connecting the PSU and a car battery recharger in series for a while before realising it was a bad idea and not worth it.

The mosfets can only handle up to 24v yet even that is hard to supply at 10A or more without buying a lab power supply which would cost me some $300+ at my local electronics store.

A note on the primary: Originally it was just 5+5 however I later rewound the primary and added the two three turn coils. I noted no difference in the output (though I have no way to measure it reliably). I know the three turn coils should be *over* the five turn coils however there isn't enough room between the black flyback chassis and the core itself to have two layers of wire.

Any tips on how to get longer arcs are welcome, as well as other comments and/or design criticisms.

Setup and arc pictures.

Dr. Dark Current

Sun May 20 2007, 05:09PM

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

Edit> I've re-read your post and now know where the additional 3+3 turns come from

however the circuit should operate fine with 5+5 turns up to some 40V (with proper MOSFETs)...
Try to wind a bigger inductor, your one seems a bit too small to me. Also putting larger "spacers" in the core sometimes improves performance.
How big is your resonant capacitor?

Myke

Sun May 20 2007, 06:25PM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

Bigger inductor and shorter wires. You don't need a lab PSU for the ZVS driver, you can use a rewound MOT, bridge rectifier, and a filter cap.

Tonic

Sun May 20 2007, 09:50PM

Registered Member #528 Joined: Fri Feb 16 2007, 10:32PM
Location: Warsaw, Poland
Posts: 166

Is it possible to achieve 100-120 DCV from rewounded MOT? And what's in general voltage output with one turn secondary coil? I have there a ~0.5kW MOT bought for 10$ and I'm going to use it for supplying ZVS driver. I will remove utterly secondary wiring, so I'll have a lot of space for own secondary winding. And I'm a 230V user.

uzzors2k

Mon May 21 2007, 03:35PM

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

It varies from MOT to MOT, but from 0.5V to 1.5V is the norm. Wind a few turns and divide the output voltage by the number of turns and you have the volts/turn. I found that 1 turn would give about 1 volt after rectification and filtering. For 100V out you will need approximately 100 turns, just to give you an idea of what to expect. I made a MOT psu a few months ago, check it out.

The voltage drops alot under load, due to the crappy wire I used. (notice that it's not one piece?) Use magnet wire, I think 20-22 AWG would give you the needed amount of turns.

Adrian

Mon May 21 2007, 03:45PM

Registered Member #697 Joined: Thu May 10 2007, 12:28PM
Location: Australia
Posts: 22

Thanks for the suggestions. I have experiemented today with a 16v low amp power supply and those extra 4 volts made a noticable difference so I can only image what 24+ would be like. I purchased a larger inductor and some magnet wire for it however I haven't had the time to wind it. (Distracted by a green laser pointer which arrived today).

Dr. Shark

Thu May 24 2007, 04:45PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

You are not the first to discover the main limitation of the Marzzilli driver: The rather exotic requirement for a power supply to run it off. Just who needs 30V these days?
There are a few options though. You can series two ATX PSU if you first lift the ground connection of one of the PSUs. Usually the output is grounded directly to the case at the screws that hold the PCB in place, cut the tracks and you are ready to go.
Another option is to identlfy the voltage feedback path in the PSU and mess with the voltage divider to trick the PSU into providing a greater output voltage. This can work very well, but can also cause a lot of problems if you don't know what you are doing.
The best option probably is to hit ebay for cheap 12V transformers with two separate secondaries, they can be put in series and even voltage doubled, and usually take abuse gracefully compared to regulated PSUs.

RickR

Thu May 24 2007, 08:14PM

Registered Member #93 Joined: Thu Feb 09 2006, 04:11PM
Location: Houston, Texas
Posts: 64

FYI, there are a couple places to obtain some pretty respectable (watt-wise) power supplies on the cheap.

BG Micro sells a 48V, 5A switching supply for USD $24.95 here:
http://www.bgmicro.com/index.asp?PageAction=VIEWPROD&ProdID=10928

and Marlin P. Jones sells a 36V, 4.2A switcher for USD $19.98 here:
http://www.mpja.com/productview.asp?product=13636+PS

Both supplies allow some minor adjustment of output voltage. I just received the 36V supply and haven't tried it out yet, but the 48V supply really works well with my ZVS flyback driver. Actually, a little too well. Most flybacks tend to fry pretty quickly. I'm hoping the 36V supply will be a little gentler.

Rick

EDIT -> Crap, I just noticed you live in Australia. Both companies above are in the US. It looks like BG Micro will ship internationally (with some restrictions). So will MPJA, but they require a USD $100 minimum order. Both supplies are pretty light so if you do decide to order, you're mostly just faced with shipping time. If you're in a hurry, modding a couple computer supplies may be the way to go.

ragnar

Thu May 24 2007, 10:48PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Live in Australia? Drop in to Jaycar Electronics and buy one of their 300W toroidal transformers. You can get them with 24V+24V, 40V+40V, etc, secondaries. Parallel them for double current; series them for double voltage.

Matt

Sparrow338

Fri May 25 2007, 01:01AM

Registered Member #661 Joined: Sat Apr 21 2007, 03:17AM
Location: Ventura, CA
Posts: 41

Since were on the topic of the ZVS flyback driver I wanted to know if these mosfets will work?

If they wont work,what are the requirements for a ZVS driver mosfet?

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