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Does anyone wind their own toroid inductors/transformers?

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Patrick

Thu Jul 12 2018, 03:19AM

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

hen and fly are right about high frequency stuff. but in your picture i think its just for current and ease of winding. one large awg gets hard to stuff versus 3 or 5 smaller awgs pulled through. all of the inductors look like powdered core material.

johnf

Thu Jul 12 2018, 07:09AM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

Patrick
rubbish go pull a panasonic inverter microwave apart and look at the transformer a beautiful example of minimum wire needed for 2kW of power transfer
the centre bit of 20awg or below does nothing @ 100khz so could just as well be a tube. Look up skin effect!!!!!

hen918

Thu Jul 12 2018, 02:14PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

Also note that the single wire-core magnetics in that really nicely designed PSU are input chokes, where the current is at 50 to 120 Hz (depending on country and whether they are after the rectification or not).
Patrick may have a point though, as the output filters (as the multi core magnetics we can see probably are) only have a small AC component, and so the use of litz wire is usually not worth the effort at saving a few fractions of a percent of efficiency.

Patrick

Thu Jul 12 2018, 11:46PM

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

hen918 wrote ...

Patrick may have a point though, as the output filters (as the multi core magnetics we can see probably are) only have a small AC component, and so the use of litz wire is usually not worth the effort at saving a few fractions of a percent of efficiency.

yes as the transformer wasnt clearly visible i didnt want to comment on it. But the powered core ones are low frequency, in this case im sure 120 or 60 Hz. at low voltage and high current the difficulty of pulling a large awg through the hole effects cost.

Im aware of skin effect and proximity effect. I believe 4 aught tops out at 125 Hz for full cross-section usage as per American NEC.

EDIT: I should mention for those of us who wind our own, large diameters relative to physical core dimensions can cause insulation thinning on the outer radius or even kinking. Small multi-strands can go through less likely to fail.

Learn how SMPS's work, there awful fun. but i may nerd out here.

johnf

Fri Jul 13 2018, 10:22AM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

Alright
My pic of the pic is
a current mode ccurrent fed supply
green cores mains in filtering single yellow core the same

triple yellow core is the current feed inductor to the the transformer switchers
Double yellow is the output full bridge inductor and the last green on the left is the EMI output filter. Nice and tidy and probably a 500watt or larger supply which is EMI quite quiet

flyrod

Fri Aug 10 2018, 02:15AM

Registered Member #61905 Joined: Sun Nov 12 2017, 03:27AM
Location:
Posts: 23

I wound another one using 5 strands (2 on top of 3):

DSCN3966s

How would I test this compared to the single large wire and the 3-strand version I posted above? The copper area of the 5 strands is slightly less than the single, but with skin and proximity effect at ~150kHz it should theoretically perform better.

Dr. Slack

Fri Aug 10 2018, 10:02AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

How would you test it? It depends what concerns you.

As you talk about wire area and proximity effect, it sounds like you're worried about losses, at a particular frequency. Find a capacitor to resonate with the inductor at (or near) that frequency, and measure the Q of the resonator. For reasonable capacitors, the Q will be dominated by the inductor.

If you're worried about other things, max current, or change of inductance or Q with current, or SRF, then test setups to measure those can be devised.

Sulaiman

Fri Aug 10 2018, 03:56PM

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

flyrod : very neat winding.

I consider winding and characterising various inductors (and transformers) to be a rite of passage for electronic engineering,
and the least understood of the basic component types.

In general I wind two types of inductor,
my 'reference' inductors which are usually heavily over-engineered
and
inductors designed for a specific application,
where the 'hard' part is deciding the design parameters,
limited by easily/cheaply available core, former and wire.

Most of my learning was from manufacturer's websites such as ;

there used to be so many manufacturers of magnetic components but now there are only a few 'Western' giants,
and Chinese manufacturer's with little or unintelligible (not English) datasheets :(

Patrick

Sun Aug 12 2018, 03:42AM

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

flyrod wrote ...

I wound another one using 5 strands (2 on top of 3):

Very nice work those parallel strands i think make for better packing effciency in your case.

flyrod

Sun Aug 12 2018, 11:49PM

Registered Member #61905 Joined: Sun Nov 12 2017, 03:27AM
Location:
Posts: 23

Dr. Slack wrote ...
...it sounds like you're worried about losses...

Right, these are power inductors. I was going to swap them out in the circuit and see if there is a significant temperature difference under similar operating conditions.

I wound them like this as an imitation of what I read here:

So they are single layer, but the copper in multiple strands can bunch up on the ID and spread out on the OD. The multiple strands should also help with skin/proximity effect.

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