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Inductors and Cores

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2005-2006 » Archive through 20 January, 2006 » Inductors and Cores « Previous Next »

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Darren
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Username: Darren

Post Number: 94
Registered: 05-2005

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Posted on Wednesday, 18 January, 2006 - 10:11 pm:   Edit Post Delete Post Print Post

Hi all,I'm making an air cored inductor winding machine for speaker crossover inductors - manual hand winding via a crank - and am planning on using PVC pipe - in various diameters - as the formers and I have 2 questions:
#1 - I'm a little concerned I may not be able to slide the PVC former out once the inductor has been wound onto it - any tips or suggestions?
#2 - If I left the PVC pipe former in the finished coil would it have much effect on the inductors value? Would I need to find the permeability of the PVC pipe to work this out?

For anyone interested, I've included an excel spreadsheet based on A.N. Thieles paper for the design of air cored inductors optimised for audio that calculates - from the required inductance (mH) and DCR - the inductors radius, height, time constant, wire size and approximate length of wire required for both 'square' - equal radius to height - and 'wide flat' - radius =2 x height - as well as letting you specify the wire size and radius you wish to use.
It also lists some standard sizes of PVC pipe for the formers and a wire gauge conversion table/list.
application/octet-streamInductor Calculator
Inductor Calculator.xls (60.4 k)

Also if anyones interested in the plans for the winder let me know, its an autoCAD drawing (.dwg or .dxf) but you'll need to find your own crank mechanism as I found mine a local scrap dealer.
Regards,
Darren
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Obiwan
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Username: Obiwan

Post Number: 61
Registered: 12-2005

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Posted on Wednesday, 18 January, 2006 - 11:16 pm:   Edit Post Delete Post Print Post

If you are using heavy wire, the coil should "spring back out" a little bit and you should be able to slide the coil off.

If you're using finer wire, Good luck. You could try some paper around the PVC first, that might make it slide off a little better.

If it's not too fine, maybe some lubricant like vasoline might help.

And if you leave the PVC on, it will not affect the inductance (at least not much). It has no iron, or other metal in it. So you'd be fine, at least at audio frequency.

If you were at very high frequency, they would have an effect. Some police radar detectors use plastic for the "antena", or at least for a wave guide.
May the Force be with you.....
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Dean_huster
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Username: Dean_huster

Post Number: 128
Registered: 05-2005

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Posted on Wednesday, 18 January, 2006 - 11:20 pm:   Edit Post Delete Post Print Post

The winder core will affect inductance. Ferrous metals increase the inductance while metals such as brass decrease the inductance. Is it possible to replace the metallic core with a plastic core? If so, splitting the core might give you some way of releasing the tension on the thing so the coil can be slipped off as well as reducing the core's effect on the inductance value. Spraying the core with silicone and/or giving it a wrap or two of plastic food wrap might help get the coil off. Don't forget to use magnet wire for winding as it is soft copper, bends easily and tends to hold its shape once bent rather than springing open when tension is released.

Dean
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Obiwan
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Username: Obiwan

Post Number: 63
Registered: 12-2005

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Posted on Thursday, 19 January, 2006 - 01:45 am:   Edit Post Delete Post Print Post

From the looks of the frist post, he's winding it on PVC, which is plastic.

Splitting the PVC (using a hacksaw or so) is a good idea, then you can colapse the PVC core a little bit and slide it off.
May the Force be with you.....
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Darren
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Username: Darren

Post Number: 95
Registered: 05-2005

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Posted on Thursday, 19 January, 2006 - 02:21 am:   Edit Post Delete Post Print Post

Hi,
Thanks for the tips. I'm also looking at splitting the pcv pipe in 4 and widening the cuts enough for cable ties to fit in the gaps. I'm going to use two discs made of MDF (medium density fibreboard) at either end of the PVC formers, with circle grooves cut into the wood - with an adjustable hole cutter - to hold/clamp the PVC - whether a single pipe or 4 pieces - in place and 4 grooves radiating from the centre of the MDF disc to the outside (also for the cable ties).The original idea for this came from a listing on ebay - see pics - and the fact there seems to be a limited range of values of prebuilt inductors for crossover applications available and their cost.
Winder 1Winder 2
Regards,
Darren

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