Over the years, I’ve had to track down a lot of parts, materials, and tools to build labs and demonstrations. Some stuff is common and some stuff is pretty hard to source, especially in small quantities.
Knife Switches: When I was but a wee lad, every general science supply house had a selection of sturdy knife switches for use in school physics labs. Though they are crude devices, they are great in the classroom because students can see exactly what it does — not too big of a deal for a simple single-pole (SPST) switch, but great for 3-way (SPDT)and 4-way (Cross-connected DPDT) switch arrangements.
These days, what passes for a knife switch is laughable. I have several that are so flimsy that the blade has to be carefully guided home or it will bend and twist out of the way. Well, if you are willing to pay for quality,
These days, not very many people wind their own transformers – at least nothing bigger than tiny electronics devices – and rewinding is largely limited to large devices that are reconditioned in specialty shops. This makes it difficult for those who want or need to wind custom devices to find parts.
Bobbins: Bobbins are nothing more than little plastic spools (square spools if you are using EI lamination). They give you a uniform surface to lay down windings on and keep you windings from falling off at the ends. It is possible to create windings without a bobbin, but that requires better equipment and is unlikely to work out for the DYI transformer winder.
Small bobbins for electronics projects can be obtained through a number of electronics suppliers, but bobbins for small power transformers are more difficult to find. With a quick search online you can find a number of vendors, but they cater to high volume manufacturing.
After a long search, I am happy to say that I have found a vendor that is willing to work with smaller orders (though possibly not for just one or two). In my case, I was looking for around 100 units. My vendor pick is Foremost Plastics. Not only did they respond without me having to call them just to get them to look at my inquiry (I’m talking to you, Cosmo Corp), but the price per unit is less than half.
To be fair, Foremost Plastics is also geared to serve those needing larger quantities (at 250 units, the price dropped in half again), but at least they are willing to talk. In addition, they do custom injection molding.
EI Transformer Lamination: For small, single-phase power transformer projects the tried and true EI core lamination is (or was) pretty standard. Originally developed as an alternative to expensive toroid wound transformers which are difficult to machine wind and use core material less efficiently. Thomas Skinner has a good selection and quick service. The minimum order is one box. Be warned this stuff is heavy. A box of EI-125 core is 90 pounds and shipping is NOT trivial! Expect shipping to add 60% to 75% to the price. Call for a quote.
Mounting Brackets: Nothing more than a little L-bracket, but these were the hardest parts in the list to find. You need four per device. For now, these are available from Edcor for EI-125 and EI-150. I say for now because Edcor has been phasing out sales of individual parts. They have a nice dimensional drawing that I include in case they need to be fabricated someday.
Magnet Wire: You can’t wind a transformer without a conductor to wind. Standard magnet wire is the least costly and can be purchased from a few vendors. Remington Industries has a nice selection magnet wire that will work well for simple devices.
In my case, I want to wind devices with dual windings and a lot of taps which makes keeping everything neat and identifiable a little more difficult. MWS Wire Industries carries Multifilar wire. This wire consists of two or more individually colored conductors that are bonded together. This wire is what is known as “bondable” wire and allows the individual turns to be bonded together without impregnating the coil with electrical varnish. Bonding can be either by solvents or heat (oven or resistance heating). The price is higher than standard wire with varnish impregnation, but for some projects, the time (and mess) saved will more than offset the difference in cost and does not require investing in a vacuum chamber or curing oven. MWS does not list prices on their website, but they are very responsive if you need information or a quote.
Stripping Magnet Wire: To me, the worst part of winding has always been removing the enamel from the magnet wire. The enamel is really tough and resists all attempts at removal. If you look online you will find all kinds of suggestions from patiently scraping with a knife, to dipping the ends in highly caustic chemicals, to (the one I ended up using) burning the insulation and scrubbing it off with fine steel wool.
I recently found an electric rotary enamel stripper on Amazon for $80. “What,” you say, “Eighty bucks to strip wire!” Believe me when I tell you that if you do more than a dozen or so wires, you will be begging to spend the money. These are kind of rare beasts, but now that you know to search for “electric rotary magnet wire stripper,” you may be able to find others. The one on Amazon comes from China and has almost incomprehensible instructions, but with a little fiddling with the speed control, I have been able to strip wire as small as 36 AWG. I believe the largest wire it will strip is 14 AWG. If you plan to get into winding, just buy one.
Winding Machines: Any thought of winding a coil without a machine will last for about half of your first coil. Basic hand-winding machines can be purchased for around $40. Here is a link to one on Amazon. You will find the exact same machine re-branded by about 100 dealers, so look for the best price. The cost jumps up rapidly from there and most aren’t that impressive. I retrofit my original hand winder with a gear motor so I wouldn’t have to try to crank it while feeding the wire. I am now working on a stepper controlled version with a feed mechanism. I’ll upload the project if I make any headway on it.