Electronics > Projects, Designs, and Technical Stuff
Toroid Winder w/o cutting the wire.
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Ian.M:

--- Quote from: Cliff Matthews on May 23, 2019, 01:13:08 pm ---Pardon my nube-like ignorance, but why don't toroid mfg's make something like an intermediate product, split in half and supplied in matched pairs with some ferrous bonding slurry and catalyst? It would make shipping them a little easier too. Winding's could cover 350 degrees of the core perhaps with the aid of 4 plastic slip-on L-rings, but would that bring down efficiency too much to be a viable product?

--- End quote ---

You can get split toroid cores - they are frequently used for retrofitting common mode HF EMI suppression. 

However for split core transformers and inductors, a pot core is generally preferable.  A pot core bobbin is cylindrical so is much easier to wind, and as the ferrite core nearly completely surrounds the bobbin (apart from the slots to bring out the winding ends, field leakage can be lower than a toroid, even if its gapped by grinding the center leg.
Cliff Matthews:
Thanks, I've seen these many times over the years, but didn't know the name. Have these been used in 60Hz power transformers?

Ian.M:
I don't think so.  At 60Hz you don't need ferrite, as soft iron is good enough and soft iron sheet stacked laminations or wound tape cores are a lot cheaper and easier to work with.
David Hess:

--- Quote from: Cliff Matthews on May 23, 2019, 01:13:08 pm ---Pardon my nube-like ignorance, but why don't toroid mfg's make something like an intermediate product, split in half and supplied in matched pairs with some ferrous bonding slurry and catalyst? It would make shipping them a little easier too. Winding's could cover 350 degrees of the core perhaps with the aid of 4 plastic slip-on L-rings, but would that bring down efficiency too much to be a viable product?
--- End quote ---

They do but the interface at the cut surfaces is critical and now the problem has been transferred to the bobbin which will occupy additional space in the winding window.

It would be better to use some other core form.
T3sl4co1l:
In fact, there are bobbins and cores made specifically for this purpose:
http://www.mycoiltech.com/et20-common-mode-choke-bobbin-four-slots-coil-bobbin_p915.html
This is snapped around a single-piece core (rectangular outline, round cross-section), and gear-driven to wind the wire onto it.

The core being a single piece, it can be made out of high-mu ferrite; but what's better is, with no air gap whatsoever, it maintains that high mu after assembly.  Up to 15k mu_r is achievable.

Tim
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