coils still- but not forever

[rick]

well after a little more investigation,found a formula


that seems to be close to that desired---how close


are the results ???? maybe not too far off---recalling


the inductance of past coils made----so if any are


interested-----stoped to find again--me get better


on this 486 fancy box--kind of cute--but the code


is quite inefficiant anyway


http:www.uslink.net/~cybercir/cir23.htm--you look


glad those boys do--


This shows how to design air core inductors. In the above formula: L= inductance in microhenries,


a= average diameter of the coil in inches, b= length of the coil in inches, c=radial depth of the


winding in inches, n= total turns of wire.


Source: "Radio-Electronics" Magazine, Nov,88 issue (C) Copyright Gernsback Publications, Inc.,


1988


L=.2a^2n^2/(3a+9b+10c)


this does not take gauge into consideration and for a round shape----would not expect inductance to change


much (orde of magnetude) if shape coil to elliptical


me shut up and push button now----

[Carl]

Re: coils still- but not forever

Rick -


I'm pretty sure I have that issue of R-E. My recollection is that the formula is valid for long inductors where length > radius, or something like that. I will try to dig up the article.


If I cannot find any reference material for scramble-wound short coils then maybe the best thing is do it experimentally. For that, I need to finish the coil winder I'm working on.


- Carl

[rick]

Re: coils still- but not forever

hi carl--


the pictorial on the web site shows a long solenoid


type structure---the coils made here are generally


on a plexiglass form with easy measure of dimentions.


by a resistance measure can get close on the number


of turns---by resonance with cap of known value


(though Q is a little wide sometimes) carefull


peaking---can attain inductance value--by experiment.


then by plugging in values into formula mentioned,the


delta was not too far different---so close that just


tweeking the frequency a little from what was called


peaked--now difference is on the other side....


should be interesting to see you come up with---


question--you make coil winder--mine all by hand--


tedious but no production requirements...running out


of magnet wire----not like old days 1lb/4.95


regards rick

[JIMI]

Re: coils still- but not forever

Hi folks, thought I would pass on a couple of techniqes I have used and still use to make coils.


#1 I cut a master form out of plywood, 1/2" 5/8" or whatever I want ro use in the diameter I want. Then I make a couple of sides about 1" more in diameter and screw them to the sides. As i wind the coil I use a wood dowl or bolt through a hole in the side as a handle and just let it turn on a small shaft, counting the turns as I go. When done just remove the screws from one side and tape the coil before removeing it.


#2 I am currently experamenting with using PVC as a form buy cutting it in half on a table saw and then gently heating it to make my bends. You come out with a PVC u that you wind the coil on.


Just a couple of thoughts to pass along.


JIMI


>well after a little more investigation,found a formula


>that seems to be close to that desired---how close


>are the results ???? maybe not too far off---recalling


>the inductance of past coils made----so if any are


>interested-----stoped to find again--me get better


>on this 486 fancy box--kind of cute--but the code


>is quite inefficiant anyway


>http:www.uslink.net/~cybercir/cir23.htm--you look


>glad those boys do--


>This shows how to design air core inductors. In the above formula: L= inductance in microhenries,


>a= average diameter of the coil in inches, b= length of the coil in inches, c=radial depth of the


>winding in inches, n= total turns of wire.


>Source: "Radio-Electronics" Magazine, Nov,88 issue (C) Copyright Gernsback Publications, Inc.,


>1988


>L=.2a^2n^2/(3a+9b+10c)


>this does not take gauge into consideration and for a round shape----would not expect inductance to change


>much (orde of magnetude) if shape coil to elliptical


>me shut up and push button now----

[rick]

Re: coils still- but not forever

thanks to respond too jimi...


more thoughts the better....


presently use sheet acrylic to make bobins for


permanamet form----


example--take single strength sheet and cut out


3 "donut" shapes--say 2)5"od x 4"id and


1)4.25"od x 4"id////sand smooth edge etc.


now use acrylic cement to make sandwich assembly


(of coarse there are certain technics to follow


such as clamp 2x4 in vice with hole in it for jig


saw blade to keep plastic flat--no bounce cut slow


at slow speed else plastic melt tablesaw surface


flat reference when cement together sandwich ultra


clean less dust make surface not touching---)you do


correct and smile---now in this case bobbin


round (can be ellipse or any shape) 5"od x 4.25id


hence a channel 3/8"deep x ~1/8"wide (use 1/4" or


??? for center ) you smile----line with al. foil


for channel---leave space less 1 turn winding


shunt field........cut 2 plastic face --to make mount


shaft etc....

[Carl]

Re: coils still- but not forever

>hi carl--


>the pictorial on the web site shows a long solenoid


>type structure---the coils made here are generally


>on a plexiglass form with easy measure of dimentions.


>by a resistance measure can get close on the number


>of turns---by resonance with cap of known value


>(though Q is a little wide sometimes) carefull


>peaking---can attain inductance value--by experiment.


>then by plugging in values into formula mentioned,the


>delta was not too far different---so close that just


>tweeking the frequency a little from what was called


>peaked--now difference is on the other side....


>should be interesting to see you come up with---


I read through the article and found nothing suggesting a length limit so maybe the formula is valid for short coils like your measurements suggest. Probably needs a slight "fudge factor" added.


>question--you make coil winder--mine all by hand--


>tedious but no production requirements...running out


>of magnet wire----not like old days 1lb/4.95


The only source I can find right now is Mouser, 1lb/$12 or 8lb/$75. Have you ever tried wire wrapping wire instead? Thicker insulation should give lower interwinding capacitance. More expensive, tho.


- Carl

[rick]

Re: coils still- but not forever

hi carl--


thanks to look up--have to get new mouser catalog--


if price for 38ga not too bad--did not look


at mail order--kind of my problem/way----if you


cant get local,dont buy else get spares...but they


?mouser,$25 min order/shiping etc...local motor


rewind shop not too bad--but only to stock gauge..


even still thanks to mention---me find out.


you keep old magazine ref.---same here...run out room


though..thanks to read/comment....wirewrap--no


but if coil is for low c--low l--nice thoght--if


only a few turns as pi can be--?--rg174 use shield


as faraday shield and center as loop...18c/foot


anyway no more guess coil inductance so much +


more---sharp people here and on eric fosters too..


friendly (for most part)


rick