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question regarding DC link inductors for ZVS circuit

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Ash Small

Fri Aug 17 2012, 10:43PM

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

Harry wrote ...

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

I picked up a couple of audio amps on Freecycle yesterday

I'm planning on using car batteries for the ZVS.

If I wanted to use a xformer I'd probably try a welding buzz-box (I have a few lying around), look out for my 600A rectifier thread (coming soon)

Harry

Fri Aug 17 2012, 11:10PM

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

600 amps?!?! I'll keep an eye out for that!

Sulaiman

Sat Aug 18 2012, 12:15AM

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

I doubt that a 50/60 Hz inductor will work well at zvs frequencies
- but in unexpected ways it might.

and the matching primary capacitor ???

Ash Small

Sat Aug 18 2012, 09:42AM

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

Sulaiman wrote ...

I doubt that a 50/60 Hz inductor will work well at zvs frequencies
- but in unexpected ways it might.

and the matching primary capacitor ???

I assume there is a misunderstanding here.

This inductor isn't for the zvs driven transfomer, its for the current limiting inductor in the positive supply rail.

Steve Conner

Sat Aug 18 2012, 09:59AM

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

Maybe refer to it as the DC link inductor to avoid confusion. Current limiting inductor is definitely the wrong name: inductors do nothing to limit DC current.

A 50/60Hz toroidal transformer is the worst DC link inductor you can imagine. It has lots of inductance, but it saturates very easily. However, due to the easy saturation, they work well driven by a Royer oscillator in ferroresonant mode. (that is to say, DC link inductor left out, frequency controlled by saturation.)

m4ge123

Sat Aug 18 2012, 10:20AM

Registered Member #4118 Joined: Mon Oct 03 2011, 04:50PM
Location: MD
Posts: 140

The inductor you're referring to isn't for current limiting; it's just to keep constant current flowing into the circuit. Basically, do what Steve said, but you should make sure the input inductor has at least 20x the inductance of the tank inductor (a bit more is better) and won't saturate too much. You can find a graph and formulae to calculate saturation here

Ash Small

Sat Aug 18 2012, 10:40AM

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

@ Steve and M4ge, thanks fr the input, I'll change the thread title to 'DC link inductor'.

(I suppose it's more of a 'current controlling inductor' than 'current limiting inductor'

)

This thread is certainly answering most of my queries regarding these inductors.

Sulaiman

Sat Aug 18 2012, 09:40PM

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

I (briefly) posted this yesterday then when I saw mention of 600A changed it to my post above, it may add a little;

Ash Small,
a couple of thoughts;
1) The (Cotswold Electronics) transformer cores would not make good inductors for the dc link in a zvs because they are almost certainly strip=wound steel cores,
(a thin ribbon of steel tape wound up) and are the best choice for small ac power transformers im many ways.

2) the VA (power) rating is pretty much determined by the weight, so if you find a similar weight toroidal transformer your VA will be close enough to that.
e.g. 50VA/0.7kg, 100VA/1.2kg, 200VA/2.2kg for one (random) manufacturer.

3) the transformers are also inductors,
high inductance/low current primary
high current/low inductance secondary
BUT the core will saturate easily with dc
You can also just wind over the existing windings for your own value of inductance
(careful though as the original primary windings may produce very large voltages)
this way when you realise that they don't make good inductors you will still have two good transformers ;)

4) I don't think there CAN be a formula for calculating the dc inductor because each application will be different,
some will want high efficiency good sinewaves
(high inductance / low loss)
some will want as much power throughput as the core/wire will allow, running hot,
(thin wire/some small saturation allowed)
and it seems many get best power throughput when the "zvs' is not actually operating in zero-switching, so short-term overheating/core saturation can also work in this circuit.

5) I'm not sure what the other cores are, on my monitor they look Grey/Yellow,
(with a bit of research you can find different manufacturers color codes)
(being from a HAM fest they're probably some popular mix)
if you find a match you can look up the specifications,
if you can measure their Al (nH/turn2) you can measure the core and look for similar,
(amp.turns = (1 to 2) x Al/Ae) Ae=core cross-section in m2
or, as above, experiment ........

(I really must learn to be more concise ..still rambling ..sorry)

Ash Small

Sat Aug 18 2012, 10:11PM

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

Thanks for the input, Sulaiman.

Sulaiman wrote ...

5) I'm not sure what the other cores are, on my monitor they look Grey/Yellow,
(with a bit of research you can find different manufacturers color codes)

Apparently these are standard colour codes, green/yellow indicates type 40 ferrite (not actually ferrite at all, but as follows):

Ash Small wrote ...

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 (MnZn NiZn)), 81 AL(nHï¼NÂ²), Permeability (ui) 60, .

I'll try and find a link that gives all the standard colour codes for toroidal ferrite cores.

Steve Conner

Sun Aug 19 2012, 07:55AM

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

I believe the colour codes were invented by Micrometals. You can see a list of the codes on their website.

Yellow with a grey top is the cooking grade of iron powder for low-frequency applications: green with a blue top is a similar but improved grade that I've used in a few projects. Either makes a fine DC link inductor.

You seem to have grey with a yellow top which is something else entirely.

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