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Old 8th May 2013, 04:49 AM   #1
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Default hand making inductors

Is it common for DIYers to hand wind there own inductors, such as the one on the output of a lot of amps?

If so, is there a guide somewhere for "how many turns at what diameter for what gauge of wire for how many henrys" out there?

Or is it more common to order them commercially?
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Old 8th May 2013, 04:54 AM   #2
Mihkus is offline Mihkus  Estonia
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I do it randomly but accurately and measure them over.
Simple task.
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Old 8th May 2013, 05:00 AM   #3
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If I don't have a tool to measure inductance, is this not a good idea for me?
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Old 8th May 2013, 05:11 AM   #4
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Many amplifier projects will specify the wire gauge and turns for the inductors.
You can calculate the inductor characteristics and be reasonably certain of its electrical properties. This will help do that.
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Old 8th May 2013, 05:19 AM   #5
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Several incarnations ago I made a few inductors for production test jigs. At that time, "Reference Data for Radio Engineers" and the ARRL "Radio Amateurs Handbook" included graphs, nomograms and formulas for air-core inductors. The folks who sold magnetic cores (e.g., Amidon, Fair-Rite, Micrometals, et al) were pretty good at publishing design aids for their particular products. Typically you had to add or remove a few turns from the calculated value to get the inductance you wanted, but once this was done the unit-to-unit repeatability was good if you took care to construct them identically. I suspect that design information is squirreled away on the 'net someplace, and I wouldn't be surprised if it has been implemented in online calculators.

If you don't have access to an LCR meter - or your LCR meter doesn't cover the range you need, or measures at a frequency far removed from the actual application - you can make reasonable inductance measurements by resonating the device with a known-value film capacitor, using your 'scope in X-Y mode to detect resonance.

Dale
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Old 8th May 2013, 06:05 AM   #6
RJM1 is offline RJM1  United States
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Online coil inductance calculator.
Coil Inductance | Electrical Engineering Tools | EEWeb
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Old 8th May 2013, 06:59 AM   #7
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At the accuracy required for output chokes, messing around adjusting inductors for precision better than 10% is really only gilding the lily. Other uses for inductors in solid state audio may be in small signal LR, LC or RLC filters but these became redundant with the development of opamps.

Considering that audio DIYs often modify output filters with choke increments of x2, x3 or a half or quarter value, it seems a waste of time and money precisely measuring a damped output choke any more than you need to accurately specify main rail smoothing caps. For typical output use, general coil winding guidelines from a trusted source will give more than adequate accuracy. From my perspective as a making one for each amplifier completed, and that's well over a hundred, I've never had a need to measure, even with repair work.

Curiosity and collecting a pile of instruments as an expression of our serious interest in electronics is another matter. Some of us like to do this and others don't understand circuit requirements and fret about things that aren't professionally made, labelled with certain values and with overkill levels of precision to aid our sense of security, too. Those are personal issues.

There are occasional designs like Quad power amplifiers, that use an RLC bridge for feed-forward error correction and this does require better precision than the simple, first order filters we usually refer to. Those, I would probably purchase with a kit or individually with the specified accuracy in any case, considering the likely one-off nature of the purchase and also the mounting requirements.

This little calculator is so easy and there is a multi-layer version on the site too: Pronine Electronics Design - Single-Layer Air Coil Calculator
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Last edited by Ian Finch; 8th May 2013 at 07:14 AM.
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Old 8th May 2013, 12:52 PM   #8
oshifis is offline oshifis  Hungary
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Look for the J.A.E.S. article from A. N. Thiele: "Air-cored Inductors for Audio". I made several inductors for loadspeaker crossovers in the 10mH order, and all measured within 1%.

Winding your own inductors
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Old 8th May 2013, 01:24 PM   #9
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I like this site for working out air cored coils... --> Mark 2 - Inductor Sim

I was winding coils for crossovers, but should be still applicable. I found I needed to up the inductance 10% on what the calulator stated to get the right value, but I was using 14Gauge wire (which is hard not to get kinks in) so using thinner wire it may work out more accurate.

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Old 8th May 2013, 02:30 PM   #10
djoffe is offline djoffe  United States
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There's also the famous Wheeler formula for inductors. Wheeler developed inductor formulas for the National bureau of standards in the early part of the 20th century.

Wheeler Formulas for inductance




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