Rolling Your Own (an adventure in coil winding) part I - diyAudio
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This is just an area I can blab on about stuff without it using up bandwidth in the threads Hopefully someone will find it interesting or useful.

Tony.
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Rolling Your Own (an adventure in coil winding) part I

Posted 24th September 2011 at 01:46 AM by wintermute
Updated 6th February 2013 at 12:09 PM by wintermute (add info about where I got the magnet wire.)

Wind my own coils, yeah why not, how hard could it be? Well if you are as much a perfectionist as I can sometimes be, pretty damn hard!!!

I suspect it would actually have been a whole lot easier if I'd not obsessed about getting a low DCR for my coils, and gone with a smaller gauge wire. As it turns out I was (obsessive), and decided to use 1.6mm (~14 AWG) wire.

I originally had thoughts of measuring off the length I needed, clamping one end in a vice and slowly turning the former (in my hands) until I wound it all on, luckily that Idea didn't last very long and I started to think about making a winding jig.

I hit google and saw some pretty fancy jigs, motorised with clutches, speed control, turn counters, that all looked too hard, so I thought about what I actually needed. Georges Transformer winding jig was in the back of my mind too, which gave some inspiration as well

The pictures below are what I came up with. I had the timber and dowel laying around. I went to Bunnings and bought some 5/16 threaded rod, some wingnuts, some masonite, and a length of 25mm dia aluminium tube. After discovering how bad I was at using a hand saw I went back to Bunnings and bought a mitre box

The whole thing went through a few iterations, and refinements. The original former ends were Masonite and held on with wing nuts (with no washers) but that didn't work so well, the wing nuts cut into the Masonite and it flexed too much.

I then got a scrap piece of 16mm MDF (which is much thicker than necessary) and cut a couple of circles out with a 70mm hole saw. Another trip to bunnings for some 5/16" nuts and washers and I was starting to make some progress.

The spool is probably the most important thing in this whole contraption. The width needs to be just right for the number of turns you need. Too small and after the first couple of layers it gets difficult to get all the windings on. Too large and turns start to slip down between the lower layer windings. In the end I found 1/2 mm bigger than the calculated size seemed to work for me.

I cut small disks out of masonite to fit into the ends of the former so that it could be centred properly on the threaded rod, the aluminium has a small notch cut in it to feed the wire down through the spool and out. The outer washer also has a small notch cut in it for the wire to exit cleanly.

Anyway below are the pictures.

1st pic shows the completed jig. rudimentary, but effective

2nd pic shows a 19.5mm former, one of the MDF endcaps, and a masonite locator.

3rd pic shows spool half assembled on the shaft.

4th pic is a close-up showing the exit point for the wire.

5th pic shows a picture of the spool ready to start winding.

6th pic shows a completed coil ready for removal from the spool.

More in part II. Hopefully I'll have another couple of coils made by the end of this weekend (and If I go well, all four of the remaining ones I need to make).

edit: (relevant for some aussies) I couldn't remember where I got the magnet wire, but a google search turned it up. It was Blackburn Electrical wires http://www.bew.com.au/wire.html . They were very helpful. I think you need to purchase a minimum of 2KG. Tell them it is for coil winding for speakers and they will recommend the best enamel type.
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Posted in Speakers, misc
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Total Comments 7

Comments

  1. Old Comment
    abraxalito's Avatar
    Is this all for passive crossover inductors? Certainly low DCR is desirable but how are you going to get around the proximity effect at higher frequencies? Losses mount significantly above say 1kHz for multilayer coils. Go active my friend
    permalink
    Posted 24th September 2011 at 04:12 AM by abraxalito abraxalito is offline
  2. Old Comment
    wintermute's Avatar
    Yes they are for my passive crossover I'm going old school. The crossover for the subs to MTM will be active.

    I've wanted to do this for about 25 years and I'm finally getting around to it. I know I could have got a MiniDsp or a Berringer or similar and gone fully active but the challenge of designing a passive crossover (with response shaping) was a lot of the fun

    I've just done one of my nominally 330uH (the biggest I'm making) ones, haven't measured it yet.

    Tony.
    permalink
    Posted 24th September 2011 at 05:22 AM by wintermute wintermute is offline
  3. Old Comment
    abraxalito's Avatar
    330uH isn't so huge for an air-cored inductor. The ones I extracted from my B&W CM1s are wound with 2mm diameter wire and measure 1.46mH at 50Hz. DCR is 0.24R, monster things - I reckon with the cost of copper I could buy 2 or 3 amp channels with that.

    Yeah I agree, if you've dreamed of this you've gotta do it to get it out of your system. But then for DSP, don't do it by halves, get an ARM Cortex M4 and program it yourself in assembly code
    permalink
    Posted 24th September 2011 at 04:15 PM by abraxalito abraxalito is offline
  4. Old Comment
    wintermute's Avatar
    Yes the small size of the inductors was one of the reasons I decided to give it a go. If I'd needed much larger inductances I may not have tried.

    The dimentions of the 330uH coil are ID 25mm OD 55mm height approx 21mm (former was 19.5mm but expands when taken off the former) and weight 250g.

    When I'm feeling in the mood for some low level programming I'll have to check out the M4
    permalink
    Posted 25th September 2011 at 01:51 AM by wintermute wintermute is offline
  5. Old Comment
    Pano's Avatar
    It's looking good Tony. Another year or two and you'll be winding your own transformers! Now that's a worthy goal.
    permalink
    Posted 29th September 2011 at 01:45 AM by Pano Pano is online now
  6. Old Comment
    wintermute's Avatar
    Thanks Michael. Are you subtly hinting I should be starting some tube projects

    Tony.
    permalink
    Posted 29th September 2011 at 12:48 PM by wintermute wintermute is offline
  7. Old Comment
    Pano's Avatar
    Not a bad idea. But you can use transformers with other stuff. I do.
    permalink
    Posted 29th September 2011 at 10:12 PM by Pano Pano is online now
 
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