A question or two...or three...about winding a coil

I was looking over some new projects as I got screwed on my last one. I purchased Electronics Projects for Dummies for the little remote control car, planning on making a rat for my cats to play with.

I instead started on the metal detector project in there. I ordered all the parts, carefully checking the list time and time again. The parts arrived and I eagerly begin assembling it.

Until...the fifth or sixth page when the author says "Insert two of the 247 ohm resistors here and there". Whaaaaaaaaat? I don't recall those on the parts list...*flip back*...nope, not there. Let's see where he's inserting them...eh, he's putting one in place of what the parts list says was a 1k resistor and one in place of a 330ohm resistor.

It was full of other major problems...needless to say I found his site and emailed him a nice "Proof-Reading for Dummies" letter.


It was a weak detector anyway, but I figured it would be good practice. I've always liked detectors, just never had one.

I found a plan for a detector called the Matchless300c, and it sounded like a good one to try. The only hesitation is you have to wind a coil, and I'm a bit confused by the instructions on winding it.

I made a little picture to illustrate where I'm confused, hope it'll make sense.

I was thinking that one turn was one time around, one image I found however showed one turn as three times around. What does one turn on a coil consist of, 1 or 3 turns...or more or less. For example, on a 50 turn coil, would it be 50 loops or 150 loops.

It says make a circle of such and such size. Insert pins here and there, and loop the wire around them. Do I loop around pin 1, then pin 2, etc?
Do I loop around the entire outer perimiter instead, making one big circle around the pins as I go?

Sorry if this seems stupid, figured I'd give it a shot. 



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NICE! Glad to have that mystery cleared up, and the advice about the insulated wire.

One last question if I may.

I'm looking at the picture I'll post with the reply, the guy used a dinner plate (plastic) to house the coils. The coils seem huge compared to what I'm visualizing in my mind.

Most coils I've see have the windings touching or really close, wouldn't a small coil like a coil made from 30swg wire that wound 70 turns on a circular former 120mm in diameter turn out to look like a stretched out phone cord (the curly kind) with the coils far apart once it was shaped like the picture?

That's the last bit of trouble I've got ...currently  . It doesn't seem right in my head, of course the only thing that seems right there is the empty space...and the voices.

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I wonder if those plates maybe smaller than I am imagining too. They look like the huge dinner plates I have in my home.

I only have some 22awg (awg=swg?) at home. I assumed swg and awg are the same and that 30swg would be a deal smaller than the 22 I have.

I kind of did a coil that size on a piece of paper using a small wire scrap I had in my jacket pocket of 22awg wire(must have fallen in there last night).

I made the lines on the paper to represent the coil of wire and then tore it off and bent it into a D shape. It seemed so small. Like it would amount to a cracker on that plate, instead of the monster plate covering coil I see in that picture. I'm guessing the 30swg would look even smaller.

Guess there's nothin left but buy some wire and give it a go. 
Aw poo...I think I see what I was visualizing incorrectly.

You don't take the coil off the former and make a loop from the front to the back right?

I was thinkning..."Ok, wind the coil, take it off and I have a nice long spring that I stretch out into a D shape." I wasn't thinking "Ok, I have a loop...I take that loop and just stretch it into a D shape." I was thinking I have to take that spring and stretch the front end to the back end to form the D.

That's what I was thinking...argh. I have way to many projects, trying to build this thing, write a book, create a video game (modelling, coding). I guess I got too many brain cells spread in different places and to few to go around.

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		Quote:			Posted by trickyspark
	I wonder if those plates maybe smaller than I am imagining too. They look like the huge dinner plates I have in my home. I only have some 22awg (awg=swg?) at home. I assumed swg and awg are the same and that 30swg would be a deal smaller than the 22 I have. I kind of did a coil that size on a piece of paper using a small wire scrap I had in my jacket pocket of 22awg wire(must have fallen in there last night). I made the lines on the paper to represent the coil of wire and then tore it off and bent it into a D shape. It seemed so small. Like it would amount to a cracker on that plate, instead of the monster plate covering coil I see in that picture. I'm guessing the 30swg would look even smaller. Guess there's nothin left but buy some wire and give it a go.  Aw poo...I think I see what I was visualizing incorrectly. You don't take the coil off the former and make a loop from the front to the back right? I was thinkning..."Ok, wind the coil, take it off and I have a nice long spring that I stretch out into a D shape." I wasn't thinking "Ok, I have a loop...I take that loop and just stretch it into a D shape." I was thinking I have to take that spring and stretch the front end to the back end to form the D. That's what I was thinking...argh. I have way to many projects, trying to build this thing, write a book, create a video game (modelling, coding). I guess I got too many brain cells spread in different places and to few to go around.

There is this to consider: take a 6.55 inch dia. coil and flatten one side and it makes half (a D) of an 8 inch coil... one D = 1/2 the circumference plus the diameter: the circumference of an 8 in coil = 25.132 in; half of this = 12.566 in; add 8 in = 20.566 in or the circumference of a 6.54 in coil.... this is in the instance of two individual coils

It just SEEMS small.

On winding the coil, if you go in and out(NOT around the pins and NOT a loop) you can create what is called a honey-comb winding; an odd number of pins are required, to do this, so the wires cross, rather than lay parallel.... this reduces inter-winding capacitance, it is handy for VLF coils.

Unless you have an LC bridge, to measure the inductance value, of this kind of winding, you should stick to directions.

This summer, there was some conversation about litz wire (technically, automotive wire is litz wire, being multi-strand,) and my digging said wire separation had a better effect, because there was less inductance loss, with more separation. Again, if you have an LC bridge, you can play with this, by making your (directed) regular coil, measure the inductance; wind either or both: one honey-comb and one with thick insulation, and multistrand, measured to the same inductance, and try them out to see which works best.

AWG and SWG are different, but I have to look it up to tell you the difference. It is like Troy (metal, gunpowder, rocks) ounces and Avoirdupois (the regular) ounces. Why not use a metric wire gauge and make it international?? I have never seen one but I am sure it exists... hey Google them!

Well, I have had (long ago) directions for two D coils but winding one coil and giving it a twist seems to produce the same effect, so yes, give it a twist, a flick of the wrist and it should be OK.. but I just thought, if you put a twist in it, the diameter is MUCH smaller. How large IS the starting diameter? Now you are getting me confused!

If you are going to twist it, why not wind it as two interconnected Ds, to begin with? Phase? 

The first D type coil I ever saw was actually formed with two independent coils, formed into ovals but set up just like Ds.

I have been thinking of trying to find some #16, automotive wire, and trying it. Heavy!

I want make a PI detector and am going to make a pancake coil of speaker wire, easy to pre-calculate values, and lower loss, in several ways. I figure my SMALLEST coil is about 14 inches but if I used #16 auto wire, it could be smaller.

Anyway, I need and LC bridge first. 

goldigger

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		Quote:			Posted by GoldDigger1950
	Brian, we differ on one thing. Going in and out of the pins is a trick of play, not an actual piece of good advice in this case. The coil is not normally calculated for scatter winding, which is what you do when you zigzag. While it may be an interesting exercise, there won't be any guarantee of the impedance being as you calculated it. Unless the designer specifies scatter winding, don't do it.

That is what I said! 

I guess we speak two different dialects of English... I understand your dialect but mine is Greek to you! 

goldigger

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