Any tips for toroidal transformer winding. ?

"N_Cook" wrote in news:gpgiki$eoa$ snipped-for-privacy@news.motzarella.org:

Some ideas that may help you. Some have been used successfully winding smaller toroids.

Use a 'throw away' tie wrap to give you a handle with which to hold the core. You can clamp the tie wrap in a fisherman's fly-tying vice and position the core in a convenient position, with the hole horizontal.

Pre-cut wire to length needed. (calculate amount needed or estimate from a trial run using short piece of wire). Better to end up with some excess, rather than too short. Use the 'average length' for a turn. Average turn length will be the average between the minimum length (a turn snug against the core) and the maximum length (pad the core to simulate maximum number of turns of wire already wound).

When winding, pass half your wire through center of core. Then alternate winding turns with each end of the wire. Pull each turn 'tight' so you don't run out of room for the wire.

Be careful not to pull too tight and damage the insulation on the sharp edges of the core. You may want to remove the sharp edges with a file or the corner of a whet stone before you start winding your wire onto the core. You can use a short section of thin tubing, such as that salvaged from an old telescoping antenna, as a 'needle' to push/pull the ends of the wire through the center of the core if the wire isn't stiff enough to serve as its own needle.

Start with the wire doubled if you want to wind 'two windings' of the same number of turns.

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Thanks, thats more than I'd found googling. I think its beyond a fly-tie vice. I was thinking of some slabs of lorry innertube fixed to the jaws of a Black & Decker workmate and work at the side edge of the workmate. Maybe use softer rubber, only at the thought experiment stage at the moment. Doubling up is probably ok for secondaries but I'm not a believer in doubling up for primary windings , too much voltage over too little laquer.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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If this transformer is to be used for a 'mains' transformer, like an isolation transformer - DO NOT DOUBLE UP THE WIRE!

first wind a prmary then layer well with kapton tape then wind secondary

you may also find that you will need to add an extra turn(s) to the secondary to make up for losses and get the voltage through as 1:1 under load.

Robert