Wire coating?

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Volter
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Wire coating?

Post by Volter » Thu Feb 24, 2011 8:39 am

What is the wire used for winding transformers? That’s a coated wire but in what?
Thanks.

ltx71cm
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Re: Wire coating?

Post by ltx71cm » Thu Feb 24, 2011 11:06 am

Enamel coated wire also known as magnet wire.

Robert Reed
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Re: Wire coating?

Post by Robert Reed » Thu Feb 24, 2011 5:43 pm

The wire is indeed enamel coated (actually a type of varnish). However for transformers and motors the coating is thicker and formulated to stand up to more heat as opposed to radio frequency coils for example. In my experience with a vast majority of coils,inductors and so on, the high temperature varnish is always a darker and redder color than the light duty stuff.

Dean Huster
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Re: Wire coating?

Post by Dean Huster » Mon Mar 07, 2011 8:07 pm

Actually, I believe the term "magnet wire" refers not to the method of insulating, but to the fact that the wire is soft copper and will remain pretty much bent to shape when winding a coil rather than trying to play "spring" with you. The insulation for "varnish coated" wire can vary from varnish/polyeurethane to a thin plastic coating. Some of those varnish-coated wires can be twisted together and soldered without removing insulation as the coating melts at low temps. Most of the stuff must be scraped to bare copper for proper connections.
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

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rshayes
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Re: Wire coating?

Post by rshayes » Tue Mar 22, 2011 10:59 pm

I suspect that the term "magnet wire" refers to one of the earlier uses of this type of wire, winding electromagnets. In general, magnet wire is solid wire with the insulation applied as a thin film (a few thousandths of an inch). This allows a maximum amount of copper in a given cross section area of a winding and reduces the resistance of the winding and thus the loss in the winding.

A wide variety of materials can be used for the insulation. "Enamel" used to be used almost universally, but is less widely used now. "Formvar" is fairly common. It has better temperature and adhesion characteristics than enamel. Other materials can be used for higher temperatures, such as teflon, but this is used only when high temperature characteristics are absolutely required. Most of these insulations have to be mechanically removed. Some can be removed with special solvents, but this is much rarer. The solvents are specific to certain kinds of wire and a pocket knife is usually easier to find.

Small wire (above #30 or so) is difficult to strip mechanically without damaging the wire. These sizes of wire may have a nylon based insulation which melts below the temperature of molten solder. When solder is applied, the insulation melts and floats to the surface of the solder.

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MrAl
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Re: Wire coating?

Post by MrAl » Wed Mar 23, 2011 1:57 am

Hi,

There is also a special tool made for removing the insulation coating from 'magnet' wire. It appears as a bunch of rotating razor blades with space in the center where you insert the end of the wire and it strips off the insulation without damaging the wire. I havent seen one of these things in years though.
Way back when i used thin 'magnet' wire for various high density circuit wiring, i used to use a solder pot and dip the end into
the solder pot for a few seconds to 'tin' the end of the wire. That worked pretty well. I had made a small solder pot with the casing from an old heavy current diode and stuck that in the tip of a Weller heavy duty soldering gun. Worked pretty good.
I could probably dig up a photo of a wiring job, but unfortunately i dont have any photos of the rotating wire stripper.
LEDs vs Bulbs, LEDs are winning.

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reloadron
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Re: Wire coating?

Post by reloadron » Wed Mar 23, 2011 8:09 am

Hi Ya MrAl
There is also a special tool made for removing the insulation coating from 'magnet' wire. It appears as a bunch of rotating razor blades with space in the center where you insert the end of the wire and it strips off the insulation without damaging the wire. I havent seen one of these things in years though.
We had several of them laying around here at work. They may have been trashed. The rotating blades were adjusted for wire diameter using certified gauge pins. We use miles of wire in gauges like AWG 16 1/2 (odd gauges). The biggest problem with the rotary strippers was they do tend to knick the wire. We would find trace amounts of copper flake in the stripped off coating. For simple everyday applications like motor windings this is no big deal. When making motors for use in nuclear reactors it becomes a real big deal. :(

Currently we use a brazing torch to heat the wire ends several inches back and literally bake the enamel off the magnet wire. Then the baked ends are cleaned. This method works much better than the rotary strippers which although looked good we could never get approved for nuclear processes. There were a few in one of my junk rooms. I'll have to see if they still exist. Some examples can be found here. They come in assorted flavors and styles.

Ron

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