Make air core inductor of 5.6mH, and impendance is less than 0.5Ohm - Page 1
Forum section: electronics / beginners

author: BZTrafo
author_rank: Newbie
timestamp: March 13, 2023, 07:17:10 am
content: Is it possible to make an air core inductor with 5.6mH value, but its impendance is less than 0.5Ohm?

author: SeanB
author_rank: Super Contributor
timestamp: March 13, 2023, 11:07:29 am
content: Yes, but going to be a good few kilograms of copper, or aluminium, flat insulated rectangular section wire that is wound on a former. Really large volume as well. If it is intended to act as a choke you will probably be better off with a large ferrite core with a large air gap, or even, for lower frequencies, a E I laminate stack with an air gap in it.

author: wasedadoc
author_rank: Super Contributor
timestamp: March 13, 2023, 11:47:44 am
content: Quote from: BZTrafo on March 13, 2023, 07:17:10 amAssume you meant resistance, not impendance (sic). Impedance is frequency dependent.

author: jonpaul
author_rank: Super Contributor
timestamp: March 13, 2023, 11:57:02 am
content: Yes one can design any rating of aircore inductor, dépends on the voltages, power, temp rise, duty cycle, freq etc.Pictured air core HV inductors are different L but gives an idea.....#1 75 kV HMI arc lamp ignitor series injection secondarySize ~ 100 mm #8 SQ single layer perfect lay#2 MRI pulse test inductor.....size ~ 1 m , #4 RECT Cu HPTZ, single layer perfect lay on G-10 FR4 custom frameEnjoy!~Jon

author: inse
author_rank: Super Contributor
timestamp: March 13, 2023, 12:11:20 pm
content: I have a 2.2mH with 0.3Ohm resistance and it’s made of 2mm copper wire, ca. 1kg.Maybe you can extrapolate to 5.6mH.That’s why I switched to a transformer core coil for 5.6mH

author: jonpaul
author_rank: Super Contributor
timestamp: March 13, 2023, 02:59:00 pm
content: iron core,totally different chararistiscs than,air.Depending upon the voltage, etcj

author: inse
author_rank: Super Contributor
timestamp: March 13, 2023, 04:04:52 pm
content: I measured the inductance vs current up to 10A, it did not saturate and the other parameters were not relevant for my purposes.What relevance should the voltage have, by the way?

author: jonpaul
author_rank: Super Contributor
timestamp: March 14, 2023, 02:46:20 am
content: Voltage...A LVPS filter L may have little,V across it.A HV series Lfilter can be elevated to many kV to ground.An HV pulse inductor may have 10s of KV pulseThus the application and voltages are importantj

author: BZTrafo
author_rank: Newbie
timestamp: March 14, 2023, 05:22:42 am
content: Thank you for your help. I'm going to use the inductor in lound speaker, and needs best audio quality, ferrite core maybe is not a good choice.

author: inse
author_rank: Super Contributor
timestamp: March 14, 2023, 05:41:35 am
content: Good luck, you are going to need a couple of kg‘s of copper, as SeanB already noted.

author: jonpaul
author_rank: Super Contributor
timestamp: March 14, 2023, 11:03:17 am
content: Rebonjour....A 'inductor in loudspeaker"Pity you didn't mention in the first post. WOULD HAVE SAVE US A LOT OF TIME.1/ If you BUILD a speaker then all voice coils are in effect on a magnetized (Alnico, Neodymium) steel core of the speaker frame and magnet.2/ If you build a loudspeaker CROSSOVER (hi/lo pass LC) you MUST use aircore coils.Go to Parts Express or similar in your country, see ready made crossovers of all sorts.Also the specia caps and coi;s for the DIY X over.We would our own on commercially avail bobbins s solenoid aircore.Beware the types of caps and filter design.Very best Xover passive is the Linkewitz-Riley.Good luckJon

author: Kleinstein
author_rank: Super Contributor
timestamp: March 14, 2023, 11:38:56 am
content: One can also have the inductors for the cross over networks with ferrite or similar core, especially if they have quite some air gap. There can be a slight nonlinear effect from the magnetic material, but a laodspeaker is somewhat nonlinear anyway.Things with an air coil gets quite a bit easier (less copper needed) if a higher series resistance is accepted and included in the filter design.

author: jonpaul
author_rank: Super Contributor
timestamp: March 14, 2023, 05:36:31 pm
content: Klienstein:Yes commercial speaker X overs use ferrite slugs or bobbin cores to save cost, and space.The distortion and nonlinearity precludes the us of ferrite or iron cores in high end crossovers.We have made fine air cost inductors of modest dimensions on a round bobbin, sizes ~ 40mm.Jon

author: Gyro
author_rank: Super Contributor
timestamp: March 14, 2023, 05:52:10 pm
content: Well-gapped laminated alloy cored inductors (and autotransformers) have been used in high quality and professional speakers for decades to achieve low DCR.Edit: ^ Hyphen inserted (changes the emphasis somewhat).

author: Kleinstein
author_rank: Super Contributor
timestamp: March 14, 2023, 06:09:12 pm
content: Transformers can be a bit more forgiving than an inductor in the cross over network, as the nonlinear magnetization current only effects the load current and the input voltage still corrects. So especially a relatively large transformer with low DCR can work quite good, even with relatively crappy (e.g. quite some hysteresis) core material.The other alternative to bulky inductors is to use separate amplifier for the speakers and not just 1 amplifier for al frequencies.The gets especially attractive with modern IC amplifiers, so not really much effort for the amplifier. It is usually only the low frequencies that really need high power and this can protect the higher band speakers from excessive power.Not sure if really relevant, but one advantage of a separate amplifier is a low output inpedance to get good damping of the speaker resonance. A passive cross over may add some impedance - if cheap maybe comparable to the speaker DCR.Another point is that on can combine drivers with different efficiency. Low efficiency for the highest frequencies would hardly matter.