Coils

I've wanted to check out some things using big coils - not the sort used for RF circuits, but large coils such as might be found in a Tesla coil. I don't have the funds to special order them or to buy them pre-made (assuming they even come that way). I expect I'll have to wind my own... but...

How the heck do you do that? What sort of arrangement would work for that? Trying it by hand left me exhausted and with poorly-wound coils of insufficient turns. Surely there is some simple arrangement whereby you can feed in wire and magically get out coils.

Can anyone point me in the right direction with this? I'd appreciate it. I've already tried Google, with little success.

I also tried buying a used "coil-winding machine," but it's just a powerful motor with a chuck for holding the coil's form. No speed control at all, no reasonable controls. There is a toggle switch that selects the motors direction, and doesn't even let you turn the damned thing off. If it's plugged in, it's rotating one way or the other at full speed and power.

I'd appreciate any helpful ideas. Thanks.

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Reply to
Chiron
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[snip]

Googling on 'diy testla coil' brought up:

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Car ignition coils from a scrapyard are one option.

Reply to
Randy Day

homemade_tesla_coil.htm

Thanks, Randy. However, I am not particularly interested in making a Tesla coil; I simply mentioned that to give an idea of the types of coils I was interested in creating. Big coils, lots of windings, air core, potentially very high voltages and relatively high frequencies. Some with fairly high magnetic flux density, perhaps. I am looking for flexibility.

I've used ignition coils previously, which are OK for some uses. Unfortunately, they are limited. IIRC, they have an iron core which limits their upper frequencies.

The solution, as I see it, is to wind my own coils so that I can choose their size, wire gauge, number of turns, core, and other variables.

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Reply to
Chiron

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That's all true but, if you're asking for help, very little can be
offered without your stating what you want to do.
Reply to
John Fields

I want to wind coils. That is what I want to do.

I don't want to *have* coils, per se; I want to *wind* my own coils, so that I can adjust them for whatever variables seem interesting, necessary, or otherwise useful.

I do not have in mind any particular project to build. I want to putter around with them, as my interests may lead me. So maybe I'll want a large magnet; or a transformer of some sort; or a Tesla coil, Oudin coil, hell, I don't know, maybe even motor windings.

Maybe think of it as a sort of "teach me to fish" kind of thing. Instead of needing to track down this kind of coil, or that kind, I'd be able to make whatever I needed.

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Reply to
Chiron

..

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No magic devices. We use a lathe to wind coils. Built a little spool holder with adjustable 'friction', turn on the lathe and start counting. (We've added a turn counter.) Scatter wound coils are pretty easy, if you want something more 'controlled' then our production peolpe put a layer of tape on after each layer or two.

Maybe a foot operated AC switch would help make your coil winding machine more 'user friendly'.

George H.

Reply to
George Herold

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Look at 0:06 and starting at 1:02.

See how he's adapted a cable to allow foot control of the motor speed?

As soon as I saw that I thought "Coil Winder"!

The Foredom FCT-1 is an electronic solution that would plug right in without any 'metalworking heroics'.

Nifty!

--Winston

Reply to
Winston

I've wound a number of Tesla coils and a 1 KW induction coil with ~13 miles of wire in the secondary... According to the DC resistance, I nailed the length of wire to within 300 feet of my design goal - not too shabby out of 13 miles.

First few TC's I did were by holding the PVC tube and guiding wire on while rotating the tube in my hands. That got old fast.

I built a coil winder with a large PM DC motor. Fixed the motor horizontally, to a 2X6 plank ~50" long.

I used a reel drive motor from a computer (1" X 15" tape reels), but there's lots of "treadmill motors" these days with similar power and size on the surplus market.

For the mandrels, I laminated a pair of spruce 2X4's together, drilled a hole through the center and mounted a short length on the motor by just drilling the hole undersize and beating it on with a hammer (healthy motor with a 3/8" X 2" shaft).

I turned the mandrels using a variable power supply (24 volt battery charger with a variac to control voltage) and some wood chisels, rasps and sandpaper to make a friction fit to the 1-1/2" to 3" PVC coil forms. Turning wood is a lot of fun....

The fixed center of my winding lathe, was a construction out of wood using a 3/8" bolt as the lathe "center." Turn two mandrels and leave one on the motor and one on the center, with the PVC tube between.

Winding is a snap - took less time to build the, admittedly crude, lathe, and wind the 3" wide long coil, than it would have taken to wind the coil alone.

I wound a total of 12 coils in the 2" to 4" diameter range and had loud noisy sparks 8 feet long out of some of them.

They can easily be coated with thick layer of epoxy or varnish by leaving the coil on the lathe, rotating it slowly, while using a credit card to spread the epoxy evenly. It rotates slowly while the epoxy sets up so there are no sags and you get beautiful results.

I just set the power supply so it is tensioning the wire then hold the wire back with one hand and guide it on with the other as the motor turns. Precut masking tape holds the wire in place long enough to cement the end down (under tension).

The induction coil was the same deal, but I made four large bobbins out of 3" PVC for the cores, and 1/8" thick Plexiglas donuts for the end plates. They are 3-1/3" wide, since I had plain adding machine paper on rolls to use as layer insulation.

I'd wind a layer using the TC winder with one mandrel to hold the bobbin (and a shorter bed on the lathe for this project). A layer took about 2 minutes using #32 AWG wire. Then tape it in place long enough to paint it with quick drying varnish to hold the turns, wrap it with a layer of paper and do another. Took about a week of spare time to finish 4 bobbins with some 24 layers on the outside coils and

30 on the inside ones. Took about a month total to build the induction coil. I wound the primary in four layers and brought out the starts and finishes so I could wire them in series or parallel to use as an AC HV transformer or DC induction coil.

AC performance is ~10,000 volts and DC unknown (but jumps a 5" spark with no problems) The whole thing got vacuum impregnated with wax (using my pressure cooker on the range top with a vacuum pump attached to it filled with molten wax - the wound bobbins soaked in the oven overnight on "warm" to get the wax to flow easily)

My stove is electric - I wouldn't do it that way with gas since the paraffin is flammable and the varnish is hot and out gassing residual solvents when the vacuum pump is running. Hotplate outdoors with a fire extinguisher standing by makes more sense....

Oak box, porcelain conical turret insulators, with brass wood screws, and a largish 1930's X-ray machine ammeter on the primary, and switch box to serve different primary combinations for different voltages. The coils are potted in wax, the iron protrudes out either side of the box. Weight is ~35 pounds and it should have handles or wheels on it.

Another, perhaps easier, way to do it is with "pies." Bobbins are only 1/8" wide with plastic film side plates, and the wire is jumble wound on - depending on the large number of bobbins to provide insulation between layers. I was working from a 1930's book on the subject and just adapted what they had to modern materials.

I use the induction coil to excite the Tesla coils - I found that up to around 200 hertz the TC performs much better. They resonate at ~100 KHZ. Higher and either the iron loses are too great or the waves aren't damped out before the next spark comes along.

Reply to
default

Thanks, George. Maybe I can work something out with this motor I've got (the alleged "coil winder." Its one advantage is that it already has a counter on it. I think a foot-operated switch would be a great idea.

I wonder whether there is any sort of foot-operated switch that lets you adjust the speed... that would be a major help, since this motor turns faster than I can feed in wire (10,000 RPM).

I've been seeing people talking about PWM. I've never worked with that, but it might be something to try for the motor.

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365 useless things.
Reply to
Chiron

Thanks, Winston. That sort of foot-operated switch, that allows variable speeds, sounds perfect.

The guy who made the video seems very inventive.

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Reply to
Chiron

Wow! Thanks, "default," whoever you are. You've given me some great ideas to try. I appreciate it.

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Reply to
Chiron

(...)

Yup, just plug one of these in and tyrap your trigger to 'constant ON'. Only nine are available here, but they cost only 30.50 each!

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He does very nice work.

--Winston

Reply to
Winston

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Wow.. much to fast, in my opinion. (That actually sounds a bit scary.) We use the back gear in the lathe to really slow it down. Is there some way to rig up some reduction gearing?

George H.

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Reply to
George Herold

Another way might be to mount two pairs of fixed (not swivel) casters so the wheels are pointing up on a 2X6" board in two groups spaced so they support the ends of the tube.

The tube (coil form) rides in the valley formed between the upright casters.

Then to drive the tube with a motor... a hole drilled in the end of the coil form - straight through (two hole, in and out) and a short length of reinforced rubber tubing (think: oil lines for autos) to connect to the motor shaft to a bar run through the holes on the coil form. Hose clamps to keep the motor shaft from slipping in the tubing.

Upside - easier than turning mandrels for each diameter tubing

Downside - is the axis of the motor would have to move up and down to accommodate different diameters of tubing so it drove it in the center.

Even something as basic as a couple of V groove blocks to drop the coil form in is much easier than trying to hold them by hand.

A holder for the feed spool of wire is another necessity in my opinion. You want the wire to come off the top of the feed, and go on to the top of they coil form - to avoid kinking.

With very fine gauge wire (think: winding guitar pickups and #37 - 40 AWG) it is easier if the wire comes off the end of the spool (spirals off the axis). That kinks heavy wire but thin wire just twists and takes it.

With Tesla coils, the gains tend to be incremental. A small difference here and there can make a huge difference in output spark length (if that is your goal). One of my best coils is 26 AWG wire-wrap wire with "Kynar" insulation and silver plated conductor - coated with epoxy.

Another thing with TC's: electrostatic field control makes a difference - you don't want a point where electrons can leak off a "point" like just the diameter of the coil form - so the output terminal has to over shadow the last turns of wire - electrostatic field on the terminal suppresses corona that would emerge from the coil.

If you are doing Tesla coils - other than the obvious hazards like electrocution, there's ozone and X-rays to guard against. Ozone is a serious issue. You can smell it in the PPM range but when it increases it doesn't smell any more strong, and it can cause lung cancer (and UV light/ozone can bleach things, cause eye cataracts and damage plastics).

X-rays aren't a problem until you put high vacuum toobs (like radios used to use) on the output terminal (little #47 bulbs light green - the X-rays fluoresce the glass envelops) Regular light bulbs aren't good for X-rays they just behave like plasma globes.

Reply to
default

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Reply to
John Fields

I stumbled upon some homemade coil winding machines projects just by looking for coil/inductor formers, winding, etc on google. Didn't save the links but they sprung out pretty easily.

Reply to
asdf

This is the method I preferred. You can wind a coil by hand faster than you can around talking about it, or waste time making some contraption.

The largest coil I made was about 5' long on 10" PVC pipe.

The trick is to not stop once you start winding, and to tape the edges down if you do take a break so you don't lose tension in the winding. If it unravels when you wind it, you're screwed. Cut the wire off and start over.

Don't wind magnet wire on warm PVC either. PVC shrinks enough in the cold for the windings to loosen and slip over each other.

Winding a secondary coil is one of the easier tasks in making a tesla coil. Once you make it you're done- all the other parts including the primary require lots of fiddling with.

I'm not sure what size coils you want, but I've always liked 20 guage copper. It's strong enough to not tear and thick enough wide edgewise with a wooden block to force the windings down and next to each other as you turn your coil form. I've wound coils by throwing a PVC pipe on some felt over an open dresser drawer with a spool of wire on the other side of the room. The front edge of the drawer keeps the coil from rolling away. Save the energy wasted on rube goldberg winding machines for your spark gap.

Reply to
Cydrome Leader

mount a chuck on the back wheel of a domestic sewing machine,

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Reply to
Jasen Betts

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Reply to
Michael A. Terrell

I have to disagree. I seriously doubt you can possibly keep up with a motorized winder entirely by hand, and it was no problem for me to kludge together a winder in less time than it takes to wind one.

I used wire in the 22-32 range. The induction secondary coil has ~67,800 turns of 32 on it. No way that would be done in a week by hand.

The winder got adapted with some poly side plates and Teflon center to wind a rotor coil for a motorcycle alternator. Self supporting coil with epoxy in the layers.

I do a fair amount of woodworking, and have a small table saw, so my time to build might be different than yours.

I did a primary with wood slats supporting the wire and individual spiral grooves to hold each turn - cylinder shape, spiral, and conical versions. Rotary gap with a few blank compact disks laminated for the rotor. One of the better, simpler, gaps was a pair of 2" diameter copper pipe caps sweated on to short lengths of copper pipe to dissipate heat.

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