|Application||Amateur Radio / RF / Antennas|
|Summary||Information on Winding Toroids and working with Enamelled Wire and coatings used.|
|Date Last Revised||21st May 2021|
|Changes Made||Original article extracted from Antenna Tuner Kit document available from this Website|
|Learning Outcomes||To feel more confident with Winding Toroids and identifying types of enamel coatings.|
|Document Format||Web page|
Toroid Winding with discussion and thoughts on Enamelled Wire. This is an excerpt that was taken from the QRP Manual Antenna Tuner Instructions available on this website.
I was doing a quick bit of research on this enamelled wire (looking for the different types of enamel being used in the last 10 years) and even in the last few years, I noticed that there is a lot of forum chatter on best ways, quickest ways, best methods in dealing with removal of insulation from enamelled wire.
So, I thought for others that do not have experience with toroids and enameled wire, that I would put down my thoughts down (or even for others that find toroids frustrating because of these issues). Please note, I do not claim to be an expert.
Now there are two main types (there are more) of insulation used on enameled wire that the general consumer can purchase. This is PUR1 (Polyurethane Grade1) and PEI (Polyester-imide). PUR1 can be melted by a reasonable quality soldering iron (as I mention below), but PEI-S (Solderable) can also be melted but at a higher temperature. There are many grades of PEI such as PEI-S, PEI-AI, PEI-B, which may require stripping/cleaning with abrasive.
When winding toroids, I have always shied away from the deep red enameled wire as I have always associated it with the PEI enamels. I might be wrong on whether it is PEI and I might be wrong on assuming that these deep reds are not easy to melt the insulation away, but in almost all cases, my assumption has been right. The other issue is that unless you are buying from a specialist supplier (e.g. RS Components, Element 14, etc) they usually do not have the insulation material listed, and generally they don’t have data sheets available. Specialist suppliers like the ones mentioned above will have data sheets or they will have the words in their descriptions such as “solderable PUR insulation”, “Insulation Material PUR”,” Insulation Coatings : Polyurethane 180” and “Solderable PU Enamelled Copper”
I prefer to use the Enamelled Wire that I get from a local electronics shop which is more of a “gold coated” enamel (and I am assuming that it is PUR). This “gold colour” enamelled wire, when you present a tap (toroidal tap) or the ends of the enamel wire with a blob of solder, the enamel melts/burns away (under a good magnifying glass you can actually see it bubble away), and tins the copper wire at the same time. I find I have a less likelihood of dry joints when using this wire.
For those in Australia, this can be found at Jaycar Electronics with the following URL https://www.jaycar.com.au/0-5mm-enamel-copper-wire-spool/p/WW4016. And I found they sell it via Ebay as well.
If you look at the following picture in figure 1 (which I have left large to make it easier to see), the tinning of this enamelled copper wire was completed in roughly 7 seconds with no sandpaper or emery board. It required a temperature-controlled soldering iron at 350 degrees Celsius (for the taps I turn it up to 370 degrees), and a blob of fresh solder, in other words with the iron on the end of the copper wire, let it build a ball until you see the enamel coating disappear (bubble), and the copper being tinned. It is a little bit of an artform, but it is achievable with a good soldering iron, and believe me it is a lot more reliable than using emery paper or scraping the wire.
I can’t tell you what the coating this is exactly (I am assuming PUR1) but pleased that it appears to have a melting point around the 370 degree Celsius mark (at least that’s what the Soldering iron was set at).
So in summary, if you have some simple toroids, its not going to make too much difference what enamelled wire you use, but if you are doing some complex toroids with multiple taps, you will find that your choice of enamelled wire could save you a few hours of work, or possibly even throwing your project out the window in frustration.
Finally one more thing. You may find others talking about running PTFE tape (plumbers thread tape) around the toroid. I generally use the PINK tape (still called plumbers tape) which is thicker than the general plumbers tape. I don’t always use it, and may depend on the likelihood of the toroid scraping the insulation on the Enamelled wire (packed windings), or if it is going to be outside (balun etc), then I normally use it. If unsure whether to use it, just use it, you wont be worse off and actually adds a bit of movement resistance to the windings moving round the toroid.