Winding your own inductors

Kornbread

   How hard is it?  Does it make cents to wind your own?    

   Wolf, can you post some pics and a how-to of your winding jig.   

Wolf

I'll get back to you. I'll have to find my photos. If you want to go to the 'Bucket account, you can find the Koylz folder and they should be in there.

You can't 'make money'(cents) winding your own, but you can save a bit. a 10# spool of whatever gauge will run you about $100. I buy from Temco through Amazon, the twice dipped type. The worthwhile gauges are 14-18. I got about 8 various coils from a spool of 14AWG. If you go to 12AWG, you get less than what I would call long enough for most winding use, and the hand cramps are easier to get. I use an LC meter, but a DATS/WT3/WT2 will also work.

I set the spool between my feet rolling toward the couch so I can control tension. I turn the jig by hand to wind.

Wind a bit, and pause where you think it's close. I use a big binder clip to hold the wire in tension to the jig plate while I spot measure. Scratch off some of the insulation carefully just enough to get a reading. Too long? wind back onto spool. Too short? keep going. The scratched area will be covered by the next layer anyway, and in finale, I dip mine in polyurethane and let dry.

Kornbread

   Guess I should have said save cents, not make.  Hadn't tried Amazon yet, but ebay had 10lb rolls of Temco 16awg for <$100 shipped.  I was curious as to how many various size coils that might make and how much money that might save, or if it would even save enough to be worth the bother.

   Have a couple old electric motors laying around, can that wire be recycled without a lot of fuss?         

Wolf

It's easier to use coiled wire from a spool than pre-kinked wire, but it can be used. The motor wire might be a pain to harvest.

As to how much money saved? I did figure it out at one point. For the 14AWG 10# spool as an example, let's call it $100. It does depend on where you buy your coils and such, but just using the 14AWG Air Erse from PE and the Solen 14AWG Perfect Lay from Mad...

I got (with very little waste, and some estimated costs):

2x 0.9mH/2x 19.99/2x $17.50(0.82mH is $17.30)

2x 1.5mH/2x 32.94/2x 22.50

2x 0.35mH/2x ~$14(0.33mH is 13.85)/2x 11.15(0.33mH is $11)

2x 0.485mH/2x ~$18(0.51mH is 18.31)/2x $13.15(0.47mH is $13)

Temco + labor = $100/Erse = $169.96/Solen(Mad) = $128.60

If you get good at it, and they look good, then you can save between $30-$70 per spool of wire you purchase.

Wolf

I also bet that the small gauge wire is likely a higher rate of return or savings. The 14AWG is just an estimation, but one that is easy to add up and validate due to the fewer units produced.

Wolf

...and I've not found a site that sells multi-tapped coils, but I assume the cost will skyrocket for premade ones. I have a proto-board on the burner with 6 coils of the multi-tap air-core variety, listed as follows:

2x 1.0mH/18 with 13 middle taps

1x 5.0mH/16 with 6 middle taps

1x 1.72mH/16(ran out of the spool, and just duplicated the second to match) with 9 middle taps

1x 0.25mH/16 with 5 middle taps

1x 0.75mH/16 with 6 middle taps

I will be getting 2x Super-Q 2.0mH, and up-winding multi-taps to 10mH for the 7th and final pieces.

All but the 1.7mH/16 and second 1.0mH/18 on each board are soldered and wired to the barrier strips. I'm trying to get this done sooner than later, and then I can combine it with the Proto-jig I built a few years ago and the soon to be done L-pad board with 3x 100W L-pads, 2x 15W rheostats, and a pair of homemade variable 10W resistors.

Yes- I am making my own version of the Box of Doom...

Kornbread

   How do you know the dia of the center gap?  How many winds, apprx length of wire, etc?  Is there an online calc somewhere to get in the ballpark?    

Wolf

There are on-line calculators, and there is an optimal geometry, but I tend to shoot for a 1.5-2" hub diameter due to the jig arrangement. I can scale the length as I see fit. It's just better to try and approximate those of the Solens, et al, to get an optimal geometry. I just wind until I hit the value, and once you wind enough coils you can kind of tell right about where that should be in your jig.

I like to use 1.5" or 2" PVC/ABS or even 2" black polyethylene pipe for the bobbin. If I don't want a bobbin, the center hub is made so I can make them bobbinless. I really like using the steel barbed plastic zip-ties for these, and I HIGHLY recommend you use a zip-tie gun to get them tight. GB types are available from Menards, but not as nice as the Ty-Wrap brand from HD, $20/100. Solen uses the Panduit brand ties, as they are the reference industrial product, but they are expensive (...and Solen does not make them as tight as I like either. I restrapped and dunked the Litz coils I bought.). Their guns are upwards of $300. I have a simple Paladin Tools product, and it cuts the ties when tight for about 1/6 the cost.

jhollander

I like to wind and unwind my own under 1 mH.  I purchase plastic bobbins on ebay and wind with a variable speed drill.  I use them mostly in tweeter circuits because I don't mind higher DCR values and there's less likelihood of melting the insulation off the wire.

The benefit is being able to get the value I want right now.  I'll post some links when I'm home

ani_101

those small values are really pesky and not always available in the right fraction! for the bigger ones, not much difference in response in rounding up or down to the next available value.

jhollander

Shavano is my favorite calculator
http://www.pronine.ca/multind.htm
http://www.colomar.com/Shavano/inductor_info.html
http://info.ee.surrey.ac.uk/Workshop/advice/coils/air_coils.html

Plastic bobbins on ebay
https://www.ebay.com/p/4pcs-53-29mm-Clear-Plastic-Bobbin-Coil-Former-FR-DIY-Speaker-Crossover-INDUCTOR/1947438767?_trksid=p2047675.l2644
https://www.ebay.com/p/Clear-28-14mm-Plastic-Bobbin-Wire-Coil-Former-DIY-Speaker-Crossover-Inductor-10/1533280743?_trksid=p2047675.l2644
https://www.ebay.com/p/6pc-38-20mm-Plastic-Bobbin-Wire-Coil-Former-FR-DIY-Speaker-Crossover-INDUCTOR/1831483489?_trksid=p2047675.l2644

I use a tapered wooden dowel to hold the bobbins then chuck the dowel up in my drill and turn away.

I know some people like precise layer stacking and that can minimize the DCR variation. However, I did some tests between slow/ neat and fast sloppy there was only minor differences that did not matter to me.

Kornbread

From the Shavano website calculator, it looks like 16 gauge and 2.5mh calls for:

                       height           rad            turns    wire dia.                        

16

0.57Ohms

0.84 Inches ( 21.42 mm)

1.69 Inches ( 42.83 mm)

142

0.052 Inches ( 1.33 mm)

400 Watts

142.0 feet ( 43.3 m)

"You'll need to be able to have the correctly sized opening to wind the core onto (the program gives that as Radius - multiply this by 2 to get the diameter) ..."

Is that correct, the coil will need to be started on a 3.38 dia. core?  Looking at the 2.5mh's on PE, they're outer dia. is about that size?     

jhollander

The inside diameter can vary. Typically I use the height as the diameter and match it to the dowel or PVC piped diameter I have when doing the big ones.

Ron_E

Wolf said:

Scratch off some of the insulation carefully just enough to get a reading.

I put a clip lead on the blade of my Exacto knife and push the blade down on the wire to take a reading.

Ron

Wolf

That's smart! Thanks, Ron!

Wolf

Wolf

Hope that helps,

Ben

Kornbread

Using the online calcs it looks like ~150ft. to make one 2.5mh.  A 10lb roll of Temco 14awg has 790ft. and costs $92, w/free shipping.  That's enough to make 5, 2.5mh coils.  PE's price on the Dayton brand 2.5mh is $31.28 x 5= $156.40.  That's considerable savings, plus you can roll any size needed.    

John, I take it your saying the inner dia. is not all that important? 

Wolf, seeing those pics helps tons.  I think I can build something similar cheaply, but it would be nice to not wind all that wire by hand.  Will need to work a cordless drill into the mix. Will wood router bits work on plexiglass?              

PWRRYD

Wolf said:

Hope that helps,

Ben

You are a coil winding mad man!

They look great Ben!

jhollander

Kornbread said:

John, I take it your saying the inner dia. is not all that important? 

Wolf, seeing those pics helps tons.  I think I can build something similar cheaply, but it would be nice to not wind all that wire by hand.  Will need to work a cordless drill into the mix. Will wood router bits work on plexiglass?              

Yup.  The brooks coil calculators give the optimal flux density (as I recall) but the inductor value is proportional to the number of turns, so a smaller diameter means more turns and less wire for the same mH.

Even running the router on the lowest speed I melt the plexi more than cut it.  I still use router bits but chip off the slag then file, sand, and flame polish to get a good edge

Wolf

KB-

Forstner/spade bits if you have them are a great options for plexi. I used a v-groove router bit at the 7" diameter for the faces of the jig, and circle-cut both faces half-depth of the plexi. Then I sanded the circumference so it wouldn't tear up my hands while in use. The rounded ends of the slots were forstner'd through, and then the center was drilled out to 1/4" for a nylon bolt. The rubber washer is a critical piece to keep the jig from loosening while winding the coils. The slots can be cut via a dremel, jigsaw with plastic cutting blade, or make yet another jig like I did for easy repetition, to use in the miter-saw. Sand the edges, and then lightly hit with a torch to polish if you so desire. I would recommend either 3x or 4x slots in the jig. More will weaken the center's strength, and fewer will allow bunching/bulging of the coil upon removal.

Oh- use the 0.23" or 0.25" plexi if available. Thinner is not strong enough, and thicker is too expensive. I built 2 from scrap pieces I had, and eventually the first one will likely fail. There are stress fractures around the bolt hole from use. If you want to make a second layer or use a large nylon washer for the center, that might be a good idea for prolonged use.

My center hub was cut with a 1.5" hole saw. I like the grip of the particle board around the hub while winding, but maybe a Delrin center might be easier to remove in use.

Craig- yes, I am! Thanks....

PWRRYD

I've salvaged a bunch of brake coils from failed hoist brakes at work.  Looks like a hundred or so feet of 19 gauge on each.  And luckily they are only taped to keep from unwinding instead of dipped in varnish.  I need to make some bobbins and wind my own small coils for future projects.

Kornbread

Mostly pieced together from stuff laying around.  A work in progress.  The SS all-thread and nuts holding the small winder in place are non-magnetic.  Hit everything with a magnet before buying anything.  Hoping they have a very small and repeatable affect on mh.              

Wolf

I like the tubing-tensioner! Great idea!

Tom_S

You could build a super cheap winding counter with an Arduino Nano clone. 

Kornbread

Initially, the hose tensioner was too tight, added some length and it worked in conjunction with the rubber washers on the crank just fine.  Would stop cranking to take a reading using a lead attached to an exacto knife (thanks John) and everything remained nice and tight. 

Problem; winding across the spool goes smooth but getting to the end of the spool and heading back across in an even manner, not so good.  Is there a trick to reversing?  If I can get the reversing figured out I think I can crank out quite a few coils in not a lot of time.    

From an earlier experiment with some 3/8" ss bolts and a tiny coil, there seemed to be a small measured change with and w/out the ss bolt placed in the center of the coil.  Was worried about this larger diameter all-thread having a larger affect.  It doesn't appear to.  Mounted was .7979mh/.26406ohm and unmounted .7905mh/.28188ohm. 

1.95mh/.398ohm and .79mh/.282ohm.  Not as pretty as Ben's but they'll do. 

 

   

Wolf

Don't forget to bind the windings by dunking in polyurethane or applying an adhesive or tape.
Thank you for the compliment!

Kornbread

Playing around with some unfinished projects that are going to need +4mh inductors.  That's a ton of wire for an air core but not so much for a solid core.  There are a few motor housings laying around that laminated steel could be sourced from.  How hard is it to figure out the amount of steel needed in a solid core inductor?   

Kornbread

To kind of answer my own question.  The dayton branded solid laminated steel? cores from 1 to 10mh show the same drawing with a 13x14x76mm core with 43mm winding length. 

jhollander

I recal seeing something that 1/2" or 5/8" steel strips are preferred in a square cross section.  Also interesting was that the individual number of strip and edges were important for helping to prevent saturation (IIRC).  Steel strips were preferred over solid core. Not sure where that article is.  I've done wood washers and a 3/8 inch bolt (fit in the drill).

dcibel

Cores are split into laminated sections to prevent eddy current losses.

https://electricalbaba.com/how-core-laminations-reduces-eddy-current-loss/