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Building a first-ZVS, inductor feedback!

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Killa-X

Mon Sept 20 2010, 12:02AM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

I never made a ZVS yet which is rather surprising. I have all I need for one on hand, except the induction coil. I already have to buy from mouser, so I took a look around. I know you want 47-200uH inductance, and you usually want a good 10+ amps. I found some that fit these descriptions, and for the lost price, it confused me. I saw some $7 ones, rated 15A. And I saw some 86A ones, for $1.

Heres the 2 I found so far.

http://www.mouser.com/ProductDetail/Murata-Power-Solutions/236R8C/?qs=sGAEpiMZZMsg%252by3WlYCkU%252bOjBV8qV5%252bXbU5Ip8DWjoI%3d

http://www.mouser.com/ProductDetail/Bourns/PM105SB-101K-RC/?qs=sGAEpiMZZMsg%252by3WlYCkUwXkpYLPJ4z4ulrdd3bYFV0%3d

Feedback would be appropriated. I just want to make sure these inductors can be up to the job, the lower price just confused me. They fit the right descriptions, but do you need it to be a specific material? I saw they allow you to select things by resonant frequency too...

Myke

Mon Sept 20 2010, 12:27AM

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

It's probably cheaper to just take something like 18 awg and wrap many turns around a ATX power supply core (the yellow & white ones). The cores work fine. I think the reason they are there is to block the AC but still allow DC to pass through and to make the supply look more like a constant current supply.

Killa-X

Mon Sept 20 2010, 12:59AM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

True but I dont have one unless I pay $25 to get a power supply. Cheaper to get one online!

Xplorer

Mon Sept 20 2010, 05:24AM

Registered Member #2416 Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91

If I were you I'd just buy a 1 inch diameter ferrous toroid off ebay. Cut two 25 inch lengths of about 24 guage magnet wire, unless you have something thicker, and twist them together to make one wire. Wind 20 turns on the toroid. That worked perfectly for me, and mine doesn't even get warm.

If you do buy a premade inductor buy one that you can add or remove windings to. If I remember correctly the inductor has an effect on the ratio of voltage to current on the output of the Flyback for a given input wattage. If you want more voltage then use a larger inductor, a smaller inductor will provide more current.

-Tony

Patrick

Mon Sept 20 2010, 07:03AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

the yellow and white inductor cores in ATX PS's are powdered metal, so there higher permeability then ferrites, and they resist saturation up to higher levels, and have a greater energy storage per unit volume compared to ferrites. the powder cores are meant almost exclusivley for DC or mostly DC input, due to reluctance and distributed air gaps. im not sure what purpose your use is, but keep all this in mind.

Sulaiman

Mon Sept 20 2010, 08:19AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

The two inductors were both very small.
Although powdered iron toroids are probably the best choice for both the dc-link inductor and the resonant transformer,
(I've used them for both),
I also like to use ferrite 'E I' cores because it's easier to wind on a bobbin,
and the airgap can be adjusted (inductance, saturation current, etc.)
So if you're experimenting you'll need either
many powdered iron toroids,
or two pairs of ferrite E I cores and some paper/plastic to make spacers.
A core cross-section area of around 1 square cm is a good start.
(more is better - as usual ;)

P.S. For the common powdered iron toroids a single layer of magnet wire wil oveheat from current at about the same current that will 'over-flux' the core.

Killa-X

Mon Sept 20 2010, 02:56PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

So really the size of these are too small. They did have some 15A for a higher cost. Sadly I don't have a computer power supply I can rip apart for one :(

I do however have a ferrite E I core. The round middle section is about 1cm diameter. Maybe 2" wide and tall and about 1.5cm deep. Think this will be big enough to at least try? I don't have a Henry meter so probably start around 20 windings?

Antonio

Mon Sept 20 2010, 11:15PM

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

The inductance of the series inductor must be larger than the inductances of the primary windings on the flyback core. So, if the cores and materials are similar, wind more turns on the series inductor core than in the primary coils.

Proud Mary

Mon Sept 20 2010, 11:35PM

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

There's no reason you can't wind a choke on one or more ferrite rods of the antenna kind. If one rod seems to be saturating, snap it in half/quarters with a file nick, and wind the inductor around the two/three/four pieces as necessary.

Killa-X

Mon Sept 20 2010, 11:39PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

Well, I talked to someone and i guess i didnt know the core didnt have to be so picky. I even heard people using iron cores. I took a Choke from a TV circuit, that was 1" diameter, and twisted 24awg together (2 pieces) 20 turns. I put 30V into it, and i get about 1.5" arcs. This stereo transformer is only rated 100W however. I've seen people get like 5" off a 12V computer power supply, but isnt this because it can demand more current, as my stereo tranny, maybe a few amps?

So far everything works, as its running at least, and making white arcs. I'm using a 400V 0.68uF snubber capacitor. Its ESR is 0.007 ohms. This was a left over capacitor from my halfbridge tesla coil circuit, and it never got hot after doing 120V 10A in. Since that is a full bridge, I had this left :)

So..If I want longer arcs, Its a mix of playing with capacitance and finding a power supply that can demand amps, correct?

Right now it draws 5 amps, and peaks 9.16 amps

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