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Old 20th February 2017, 06:08 AM   #1
Butcher is offline Butcher  New Zealand
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Default Help inductor. Parallel windings of thin wire to make one?

Hello. I am assembling 3 way crossover for stereo project.

I require air wound inductors of mH values of say 1 - 4mH. Exact values are not important here.

I have source of cheap (free) 20AWG wire (0.8mm). The DC resistance will be quite high in this case. I am building 12dB / Octave design. One inductor is in series with woofer so I would like to keep its DC resistance low for efficiency.


Question is, if I loosely twist 2 0.8mm conductors (with cordless drills assistance) in parallel and wind the inductor, Is this possible? I am looking for less than 1/10th Ω of woofer (less than 0.8Ω).

I am raiding an old F&P smartdrive washing machine motor of it's copper, if this helps anyone.


Thanks for any advice!


ps. I have made 4 x 0.36uH inductors quite happily using 0.8mm wire. I also have good (kit built Silicone Chip mag) inductance meter at hand.

Thank you. (I hope winding two conductors wont add any capacitance / inductance, causing a complex circuit etc). I am just trying to save some $$$ and have fun.

Last edited by Butcher; 20th February 2017 at 06:29 AM.
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Old 20th February 2017, 06:46 AM   #2
jcx is offline jcx  United States
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"bunch winding" is a known technique for making higher Q inductor/transformer windings

it is done as you plan - twist bundles of smaller dia insulated wire together, use as a single wire
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Old 20th February 2017, 07:38 AM   #3
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Here is a commercial product: https://www.intertechnik.com/Shop/Cr...-15/1768,en,80

IMHO, a 1mH air core does make sense, but a 4mH one not.

Ralf
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Old 20th February 2017, 07:52 AM   #4
Butcher is offline Butcher  New Zealand
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Thanks. I have wound 20AWG (0.8mm) wire and created 4 x 0.36mH aircore inductors (for 2nd order crossover, tweeter HP and mid BP) as well as 2 x 0.25mH (for my 1st order crossover) aircore inductors. Size is about 1 inch (25mm) diameter and height is less, which is respectible. My hands hurt now!

"Litz"windings is to lessen (eliminate) skin effect at microwave (RF) frequencies. I was concerned about complicating things at audio frequencies, namely non linearity! I desire good sound using home made components (personal, hobby use!)

Thanks jcx.



Mr. giralfino, why does making 4mH one not make sense? I guess making 4mH inductor would be about 10 times the size of a 0.4mH one? I understand it has to do with 'turns ratio'. I am guessing that DC resistance would be higher, due to 10 (?) times the number of turns. That would make 0.7Ω become 7Ω, which would be high ??? (8Ω + 7Ω = 15Ω)


May be I am missing something ? I am trying to AVOID iron core.

Last edited by Butcher; 20th February 2017 at 07:56 AM.
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Old 20th February 2017, 07:56 AM   #5
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Quote:
Originally Posted by Butcher View Post
That would make 0.7Ω become 1.7Ω, which would not be too bad ??? (8Ω + 1.7Ω = 9.7Ω)


May be I am missing something ?
One is Z, the other R
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Old 20th February 2017, 08:03 AM   #6
Butcher is offline Butcher  New Zealand
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"with 7 twisted, solitary insulated copper conductors"

That sounds cool.



Yes, I understand DC and AC theory, although AC makes my head Hertz (joke!)

Impedance comprises of C and R components... Thanks.


So, winding 7 x 20AWG wires in parallel and winding on rather large bobbin would work to my needs ?? I may have to work out series resistances of 7 x conductors (or what have I). ...I would like < 0.8Ω if possible (< 0.4Ω for the Z = 4Ω setup.


am I on the right track? Or is higher DC Ω acceptable for 'average' system? (Obviously less is more)

I am making two setups, one with one 12" woofer Z = 8Ω and the other speakers use 2 x 8Ω 10" wired in parallel (in phase of course )

Thanks.

Last edited by Butcher; 20th February 2017 at 08:06 AM.
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Old 20th February 2017, 08:08 AM   #7
Butcher is offline Butcher  New Zealand
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ps...

Originally Posted by Butcher Click the image to open in full size.
That would make 0.7Ω become 1.7Ω, which would not be too bad ??? (8Ω + 1.7Ω = 9.7Ω)


May be I am missing something ?




...I also corrected my math in post #4
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Old 20th February 2017, 08:34 AM   #8
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by Butcher View Post
I guess making 4mH inductor would be about 10 times the size of a 0.4mH one? I understand it has to do with 'turns ratio'. I am guessing that DC resistance would be higher, due to 10 (?) times the number of turns.
More like 3 or 4 times
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Old 20th February 2017, 08:49 AM   #9
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Twisting together 2x20AWG wires is equivalent to a single 17AWG wire. The inductance of a coil is dependent on the wire itself but also on the geometry of the coil, but expect to have a DCR of roughly 1 Ohm for a 4mH coil (*).
High DCR coils are not bad per se, but that means that some power will be wasted as heat and not passed to drivers (if a driver is in series to this coil). If a coil is in series to a midrange in a 3-way the DCR of the coil has to be summed to the resistance of a highly-to-be-there resistor, so probably not a problem, but if the coil is in series to a woofer, that DCR has to be low in order not to loose SPL.
And then there is the weight factor. Comparing two 3.3mH coils from the same manufacturer (Jantzen), the iron core coil uses 1.0 mm wire, has a DCR of 0.36 Ohm, and weights 225 g, while the air core with 1.6 mm wire has a DCR of 0.48 Ohm (still good but higher than the iron core), and weights 1Kg.
An iron core is not a devil, chosen right is the only sensible choice for a high inductance coil.

Ralf

(*) If your winding technology is good ...
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Old 20th February 2017, 09:25 AM   #10
Butcher is offline Butcher  New Zealand
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"
Originally Posted by Butcher Click the image to open in full size.
I guess making 4mH inductor would be about 10 times the size of a 0.4mH one? I understand it has to do with 'turns ratio'. I am guessing that DC resistance would be higher, due to 10 (?) times the number of turns."


"More like 3 or 4 times"



Not sure if you serious or not But they are big buggers!

It is nice to recycle perfectly good 99.9% (?) copper that was just thrown out. Good old washing machines! TV degaus (sp) coils are mostly 0.5mm D.



20-17 Gauge makes sense.



"If your winding technology is good ..."

Cheeky bugger! I read about hex windings. Stacking windings 2, then 4, then 2. Yea, might need some practice Mr. Ralf! Um, 2 + 4+ 2 = 8. Please explain hex windings. I understand that winding thus is to fill spool with max turns ... ? I am being lazy

I have AWG - mm D chart. Very interesting. I can spot pattern



1 ohm is acceptable. I now understand that the 3.6mH (Which I chose,,See below) needs to be low DC resistance for W (Woofer). this is current law, mmm, Mr, ohm, right??? Midrange not so fussy because of V Av. -Much more polarity changes...


Resistors loose energy thru heat. (So to capacitors and inductors...)


"highly-to-be-there resistor" Yes, inherent R !



"And then there is the weight factor."


Not a problem! These buggers are heavy, I take it (soon to wind one!). I will ask my mate to help. Cordless drill etc. Best way to straighten wire is with one turn around a smooth object. I settled on plastic screwdriver handle. Use about 0.9 turns and common sense!


"Comparing"

I like the way you think. establishes baseline!



"An iron core is not a devil, chosen right is the only sensible choice for a high inductance coil."

Well, permeability? would one choose bunch of old rusty nails??? I am being serious! I am aware of laminated sheets that act to prevent eddy losses?


I would like big damn 1.8mH and 3.6mH coils! Expense is no prob. My buddy made His own speaker boxes that are 1500mm high and allow for much room behind woofers, using recycled Remu wood (native NZ timber).

Link...
https://en.wikipedia.org/wiki/Dacrydium_cupressinum


I am no carpenter, but I would like to see this homemade system perform for His '80 's music!

Last edited by Butcher; 20th February 2017 at 09:28 AM.
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