How do you figure out the value of a torroidal inductor? - Page 1
Forum section: electronics / beginners

author: raspberrypi
author_rank: Frequent Contributor
timestamp: December 07, 2016, 02:48:41 am
content: Since torroids are hard to find I salvaged one out of an old computer monitor. What the math equation to figure out what the value is?Its a magnetic ferite? Its just a gray color, looks like if you dropped it would shatter, torroid (sorry for non metric I can't find one metric measure in the whole house!):7/16" thick15/16" diameter3/16" core21 turns of stranded copper 20ga wireMy goal is 350 uH or at least 275My other option is 30ga wire wrap wire and lots of spare time.What equipment would you use to build an inductor?I actually found a great starting point on Tube of You:

author: bktemp
author_rank: Super Contributor
timestamp: December 07, 2016, 07:31:40 am
content: Quote from: raspberrypi on December 07, 2016, 02:48:41 amL=n²*AlSince you don't know Al or any other properties of the material used, you can't calculate anything, you need to measure the values.QuoteAt least an LCR meter for measuring the inductance using a couple of turns and then calculating the Al value.Then you can calculate the required number of turns.If you want to use the inductor for a SMPS you also need this (because you need to know how much current you can put through the inductor until the core goes into saturation):http://elm-chan.org/works/lchk/report.html

author: chris_leyson
author_rank: Super Contributor
timestamp: December 07, 2016, 09:47:43 am
content: You could measure the inductance using a sig gen and scope if you don't have any other means,http://www.dos4ever.com/inductor/inductor.htmlI you've got 21 turns then Al = measured inductance/212

author: HighVoltage
author_rank: Super Contributor
timestamp: December 07, 2016, 11:26:48 am
content: If you have a way of measuring the inductor current with a scope, you can just use a switch, apply some DC voltage and look at the rise time "t"Then use this formula to calculate the inductance "L"I = E/R(1 – e-t/(L/R))This is a poor mans way, but it works really well.

author: ali6x944
author_rank: Frequent Contributor
timestamp: December 07, 2016, 12:01:23 pm
content: The way I would do is to create a resonance circuit and measure the frequency of the oscillation from the LC parallel resonance circuit and use this formula to find the inductance:L=1/(2*pi*f)²CWere L is inductance in Henry,f is frequency in hertz,C is capacitance in farads.See circuit here:https://plus.google.com/115108013327841958420/posts/LsGVzzE9oXo

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 07, 2016, 02:32:03 pm
content: Since it is most likely a ferrite material, it will saturate quickly without storing much inductive energy.It will, however, make a fine transformer.What was it doing, in the monitor? Was it looped around a cable, or something like that..?Tim

author: Zero999
author_rank: Super Contributor
timestamp: December 07, 2016, 07:29:27 pm
content: Quote from: HighVoltage on December 07, 2016, 11:26:48 amThat would work in theory. In practise though, switches bounce, which will make it difficult. You could use a push button to trigger a thyristor to swich the LR circuit and connect it to a 'scope set to single shot mode.

author: HighVoltage
author_rank: Super Contributor
timestamp: December 07, 2016, 09:09:15 pm
content: Quote from: Hero999 on December 07, 2016, 07:29:27 pmI used to do this a lot, long long time ago, before I had any LCR meter and it works kind of surprisingly well.As a switch I used an old Morse Key (like the one in the picture) and had no bouncing at all.If you trigger the scope for a single shot it is pretty repeatable even.well

author: K2CK
author_rank: Newbie
timestamp: December 07, 2016, 09:49:36 pm
content: I find an LCR meter invaluable for determining the inductance of wound torroids. Even an inexpensive model should get you into the ballpark.

author: danadak
author_rank: Super Contributor
timestamp: December 08, 2016, 12:46:57 am
content: You can always build your own LC meter for LF work -http://www.sillanumsoft.org/ZRLC.htmRegards, Dana.

author: raspberrypi
author_rank: Frequent Contributor
timestamp: January 05, 2017, 05:11:20 am
content: Quote from: T3sl4co1l on December 07, 2016, 02:32:03 pmWhatwas it doing in the monitor? Just kind of sitting there. Actually it had a power cable going through it.I have no equipment other then a multimeter and an SDR radio and alot of creativity. It's going into an LC circuit that will block the AM band for an SDR radio. Basically I just keep messing around with the circuit then look at how the SDR behaves.