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question regarding DC link inductors for ZVS circuit

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Ash Small

Thu Aug 16 2012, 08:13PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I picked these ferrites up at a hamfest at the weekend.

I've read (I think) that you want yellow/green ferrites for the current limiting inductor for the Mazilli ZVS circuit.

These measure 1 1/16" OD, 9/16" ID and 7/16" thick.

Are these suitable cores for the inductor for the ZVS circuit, and if so, how many turns of wire should I use?

EDIT: These are, fom what I can gather, T106-40, T106 being the dimension spec (26.9Â±0.5 mm OD, 14.5Â±0.5 mm ID, 11.1Â±0.64 mm Thick), 40 being the material, AL(nHï¼NÂ²) 81, Permeability (ui) 60, .

Forty

Fri Aug 17 2012, 05:58PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

I thought powdered iron was the way to go because of its frequency range and higher saturation point

Harry

Fri Aug 17 2012, 06:37PM

Registered Member #4081 Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139

Pretty much all toroids work, the better ones just don't get so hot

As for the turns there is no specific number, just choose a wire size that can handle 12 - 15 amps and start winding

Steve Conner

Fri Aug 17 2012, 07:06PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The inductance in the ZVS isn't really critical, it just needs to be "big enough" to smooth out the current.

A reasonable design process would be to pick a wire gauge that can barely handle the current you intend to run, and cram on as many turns as will fit on your core. If the inductance is too small, try stacking a bunch of cores.

Iron powder is the right thing to use. Ferrite toroids are not recommended, they saturate too easily with DC current. However, what you have there is a low permeability RF grade of ferrite, not the usual power electronic stuff, which has a permeability of about 2000. At low frequencies it may behave more like iron powder than ferrite.

Ash Small

Fri Aug 17 2012, 07:43PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Forty wrote ...

I thought powdered iron was the way to go because of its frequency range and higher saturation point

That's what I thought, but I'm sure a couple of people have posted on here that you should look for green/yellow toroids in ATX power supplies, so when I saw some at a hamfest I grabbed a handful.

Harry wrote ...

Pretty much all toroids work, the better ones just don't get so hot

As for the turns there is no specific number, just choose a wire size that can handle 12 - 15 amps and start winding

I assume I don't want it to saturate, so should I double up or 'treble up' on the cores? (I have plenty of them, and I assume more 'ferrite' = less heating)

I've read I want between 47 and 200 ?Henries (I'll have to check the units (micro or milli)), but there does seem to be a lack of infomation on the 'net regarding exact specs for the inductor.

EDIT: Thanks for the input, Steve, I was composing my reply and missed your post.

Harry

Fri Aug 17 2012, 08:40PM

Registered Member #4081 Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139

lack of infomation on the 'net regarding exact specs for the inductor

That's because pretty much every thing will work. I had a yellow toroid with only 6 turns on it and it still worked. I have also used a RFI suppression ring from a home cinema SMPS wound with 15 turns of standard 0.75mm wiring.
Here is a video which shows what I mean:

Apparently using a higher inductance means higher voltage, but I can't really see any difference.

I used my ZVS for induction heating once without an inductor, it drew more current but still survived.

Ash Small

Fri Aug 17 2012, 09:08PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Harry wrote ...

lack of infomation on the 'net regarding exact specs for the inductor

That's because pretty much every thing will work.

But people do say to avoid the usual ferrites that we use for HF power circuits. (as Forty and Steve have pointed out).

I picked these toroidal transformers up at the hamfest for a few quid each, which I assume have powdered iron cores, but they'd be a bit 'overkill' for this application. I'll probably use the cores for Hf chokes, though. I used a HUGE one (much bigger than these) as part of the choke curcuit in my HF TIG welder.

Harry

Fri Aug 17 2012, 09:31PM

Registered Member #4081 Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139

Yes that would be just a tad overkill! What voltage do they kick out? They might be good for powering your ZVS.I use a 30V 600VA transformer, and control it with a dimmer switch, which works surprisingly well though it probably isn't too good for the dimmer, controlling a large inductive load and such.
So to sum up you can use most inductors for the ZVS, there are good inductors and bad inductors, which heat up.
As Steve said, just cram as many turns of adequately rated wire onto it and see what happens

Ash Small

Fri Aug 17 2012, 09:53PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Harry wrote ...

Yes that would be just a tad overkill! What voltage do they kick out? They might be good for powering your ZVS.

They have two secondaries, each putting out 15 volts, which could be wired in series to give 30 volts.

Unfortunately, they only put out 3 amps (according to the vendor), so, even if I connected both secondaries in series, and both transformers in parallel, I'd only get 30V @ 6A, not really enough for a Mazilli ZVS. (Maybe I should have bought a few more

)

Harry

Fri Aug 17 2012, 10:30PM

Registered Member #4081 Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139

It does demand a lot of power, I blew the thermal fuse on my transformer after 10 minutes of arcing. Thankfully the fuse was on the outside of the primary so I could bypass it; some transformers have one that is near impossible to get to without unwinding most of it.
But if you put the 15V secondaries in parallel for 12A, then rectify for 20V after diode drop and such, that is pretty good. you could then series in another power supply, like a computer PSU for 32V, or a drill battery for 40V when it's full charged.
Get on Freecycle and see if there are any audio amps or stereos, that's where I got my transformer, from a big ass subwoofer

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