Air Cored Inductor - Page 1
Forum section: electronics / beginners

author: TorqueRanger
author_rank: Frequent Contributor
timestamp: May 15, 2013, 11:07:25 am
content: I am trying to build a Lead acid battery zapper mk3 and the circuit requires a couple air cored inductors but I can't seem to find on mouser websiteCan this components be replaced with something else with out affecting the circuit ??

author: AlfBaz
author_rank: Super Contributor
timestamp: May 15, 2013, 11:36:34 am
content: if you have something to measure inductance, get yourself some thick copper enamelled wire and wind it onto a half inch whitworth bolt. 10 -15 turns ought to get you close, then unscrew the bolt from the wound wireHere's one of those dodgy formulasL = (d^2 x n^2)/(18 x d + 40 x l)L = uHd = diameter in inchesn = number of turnsl = length of coil

author: TorqueRanger
author_rank: Frequent Contributor
timestamp: May 15, 2013, 03:43:50 pm
content: Quote from: AlfBaz on May 15, 2013, 11:36:34 amI have no other info beside the schematic info and that's it .....

author: c4757p
author_rank: Super Contributor
timestamp: May 15, 2013, 03:49:45 pm
content: That's all you need. You choose the coil size yourself.

author: TorqueRanger
author_rank: Frequent Contributor
timestamp: May 15, 2013, 03:58:32 pm
content: Quote from: c4757p on May 15, 2013, 03:49:45 pmLOL OkI asking because I have never built an inductor before and really have no clue but I am going to look up some info right now..

author: quarks
author_rank: Frequent Contributor
timestamp: May 15, 2013, 04:22:52 pm
content: Hello TorqueRanger,you really only need to have/buy some enameled copper wire like this (sorry for German, but you see what I mean)http://www.reichelt.de/Kupferlackdraht/2//index.html?ACTION=2&GROUPID=5040&SHOW=1&START=0&OFFSET=16&choose the thickness of the wire for the amperage you plan to use it with.Then wind as many times around any round object with the diameter you like (I use a pencil for example) until you get the inductivity you like to have.Pull out the pencil, strip off the insulation on both ends and you have someting looking like this (in the left side of the picture)http://commons.wikimedia.org/wiki/File:Luftspulen.JPGIf you have an LCR meter just check the iductivity of x windings and then multipy/calculate how many more or less you need compared to your test coil, until you have what want.If you do not have an LCR meter to confirm what you did, use the provided formula from AlfBaz and you will get close enough.Hope that helps.byequarks

author: AlfBaz
author_rank: Super Contributor
timestamp: May 15, 2013, 05:30:45 pm
content: The good thing about using a screw thread is you know the diameter based of the bolt size and the thread gives the wire a good guide to form the shape. As mentioned above you can choose wire size to suite current but it needs go be thick enough to hold its form.I mentioned half inch (or 12mm) and the number of turns etc, because that'll get you close to 1mH, according to that guiding formula

author: quarks
author_rank: Frequent Contributor
timestamp: May 15, 2013, 05:45:10 pm
content: A screw is great because of the guide. But when using a metal screw, there is also a small risc of cutting the insulation, that is why I normaly use a pencil.

author: SeanB
author_rank: Super Contributor
timestamp: May 15, 2013, 05:54:27 pm
content: Just wind the bolt with pipe tape if you are worried, makes it easy to unwind then. A lot of coils I made have been made on a mandrel from a paper till roll inner, it is a nice size and works well, plus it is easy to make 2 holes at each end to pass the wire through to anchor it.

author: Smokey
author_rank: Super Contributor
timestamp: May 15, 2013, 06:47:41 pm
content: One thing to watch out for with making air core inductors is that at first it seems like a good idea to just use an off the shelf spool of plastic insulated wire, which is essentially an air core inductor. But after the plastic insulation melts the first time and turns your inductor into a shorted together fused mess you will go with enameled wire.Spools of wire do make good quick test inductors if you don't get them hot enough to melt though

author: smashedProton
author_rank: Frequent Contributor
timestamp: May 15, 2013, 06:51:15 pm
content: If you have some good reference capacitors you can dind tge resonant frequency and solve for L. Cheap dodgy alternative to a lcr meter

author: smashedProton
author_rank: Frequent Contributor
timestamp: May 15, 2013, 06:52:10 pm
content: Smokey, I'm sure your name has something to do with that!

author: Smokey
author_rank: Super Contributor
timestamp: May 15, 2013, 07:26:17 pm
content: I may or may not have a couple of spools of melted wire laying aroundNow what REALLY smoked up the joint was when we over-loaded a potted transformer secondary. It took weeks for that smell to totally go away.

author: C
author_rank: Super Contributor
timestamp: May 15, 2013, 07:34:04 pm
content: Note that you can change the inductance after the coil is wound by changing the spacing of the coils.This works great to fine tune a circuitC

author: notsob
author_rank: Frequent Contributor
timestamp: May 15, 2013, 10:21:37 pm
content: That is a Silicon Chip project - issue 202, normally SC has all the details on winding/making inductors/transformers included in their project write ups. If the details are not there contact Silicon Chip, I've had questions in the past and they have been quite helpful.

author: TorqueRanger
author_rank: Frequent Contributor
timestamp: May 15, 2013, 11:15:03 pm
content: Quote from: notsob on May 15, 2013, 10:21:37 pmI tried posting up the article but it's too big and I can't seem to find any of that info and will have to try and contact Silicon Chip and see what they say...I found this and thought it would be pretty useful for making air cored inductors...http://www.colomar.com/Shavano/inductor_info.html

author: notsob
author_rank: Frequent Contributor
timestamp: May 16, 2013, 12:16:02 am
content: A correction, there were 3 versions of this project, July 2005, May 2006 & Mk3 July 2009, if you do not have the complete article, you can purchase online access to the particular month concerned from Silicon Chip.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: May 16, 2013, 02:26:45 am
content: QuoteSurely this is too low for 220uH or 1mH with an air core?

author: AlfBaz
author_rank: Super Contributor
timestamp: May 16, 2013, 05:33:14 am
content: Quote from: HackedFridgeMagnet on May 16, 2013, 02:26:45 amTo be honest, I don't know.If that formula I posted is remotely accurate then a 1/2" BSW thread is 12TPI so diameter, d = 0.5" (Although I believe its the total outside diameter including the wire), over an inch turns, n = 12 and the length of the coil, l = 1" so0.5^2 * 12 ^2 / (18 * 0.5 + 40 * 1) = 0.735uH

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: May 16, 2013, 06:58:24 am
content: I was only using the formula too, via an online calculator.I just remembered that I couldn't get anywhere near 1mH inductance in a small amount of turns without a higher permeability core.

author: Fuse_Burner
author_rank: Contributor
timestamp: May 16, 2013, 07:04:50 am
content: Quote from: Smokey on May 15, 2013, 06:47:41 pmWill an inductor even create loss/heat?

author: SeanB
author_rank: Super Contributor
timestamp: May 16, 2013, 07:09:17 am
content: Yes they get toasty, just from resistive losses. If there is a ferrite inside with a high loss any power dissipated in it will be done as heat, and in the middle of the windings where it is least able to dissipate. Thus you get crispy, and remember standard PVC melts at just over 100C, unlike enamelled copper where it can handle typically 150C with ease, and it is a lot thinner so transmits heat better out to the outer layers.

author: rf-loop
author_rank: Super Contributor
timestamp: May 16, 2013, 07:12:16 am
content: For rough estimate inductor (air core) this is handy tool:http://www.daycounter.com/Calculators/Air-Core-Inductor-Calculator.phtmlSo, half inch diameter with some few turns (example 15) is far far away from 1mHbut in uH class, yes.

author: Fuse_Burner
author_rank: Contributor
timestamp: May 16, 2013, 07:13:01 am
content: Quote from: SeanB on May 16, 2013, 07:09:17 amTYHow about at perfect resonance?Will it still present some loss/heat?

author: SeanB
author_rank: Super Contributor
timestamp: May 16, 2013, 07:24:06 am
content: At resonance the losses in the coil are at the highest, so all the power put in to keep it resonating will be dissipated as heat in the windings and core. Thus for these applications you use a ferrite with low losses, ie with a small loop in the hysteresis curve. large loop area ferrites are used for things like chokes and memory cores, as there you want to have power dissipated in the core or have remnant magnetism.

author: Fuse_Burner
author_rank: Contributor
timestamp: May 16, 2013, 07:46:35 am
content: Cool, I'm glad I asked. This works for a tank coil as well? I've been told that a tank coil presents no loss and creates no heat.

author: ConKbot
author_rank: Super Contributor
timestamp: May 16, 2013, 07:55:55 am
content: http://www.colomar.com/Shavano/inductor_info.htmlLooks decent for putting in a desired inductance and spitting out turns/dimensions that should work. Youre gonna need a lot of turns for a 1mH inductor

author: AlfBaz
author_rank: Super Contributor
timestamp: May 16, 2013, 08:09:10 am
content: Quote from: AlfBaz on May 16, 2013, 05:33:14 amBrain fart, thought another .3u would make it to 1m

author: Mar
author_rank: Contributor
timestamp: May 16, 2013, 10:16:32 am
content: if u need 1 mh aircore you will have to do handreds of turns ...i made 1 mh inductance with ferrite toroid core got from old ATX power supply ( i though its AL=92 ) .. with only 114 turn about 4 meters from 0.7mm wire diameter ...

author: ConKbot
author_rank: Super Contributor
timestamp: May 16, 2013, 01:50:43 pm
content: Quote from: Mar on May 16, 2013, 10:16:32 amYou have to mind your saturation though if you are using a core. For the desulfator, the L3 inductor, its keeping the pulses/ringing of the desulfator from affecting the charger. So it needs to maintain its inductance under the full charge current. The ATX one will work fine for smaller charge currents, but an air core will work fine until you burn the insulation.Also, if you want to buy instead of make, parts-express sells air-core inductors for decent prices. Meant for crossovers in stereoshttp://www.parts-express.com/term/1.0mh?srch=1.0mH