soldering enameled wire; repairing 110 to lower transformers


AIUI, when soldering to an enameled wire, there is no need to remove the enamel first. It just burns up and disappears when one is applying the solder. Is that true?
Otherwise, are there any tricks to repairing a small transformer** such as used to power an audio device such as a clock radio from 110VAC: I take the cover off and the first layer of "tape" and if there is only a half inch of wire going to the priamary winding, and if when I try to solder to it, it breaks off just as it goes into the winding, under other stuff, I haven't been able to fix them in the past. But maybe there is a trick I don't know.
**The one in question today has 3 secondary windings, green-yellow-green, red-red, and blue-blue. Does that indicate what the output voltages should be?
It's 1 3/4 x 1 3/4 x 1 1/2 inch and it runs a high-quality Panasonic, clock-radio, sterero cassette player/recorder. Model 680-3870
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Some enameled wire can be soldered without stripping , but I doubt it is the case in your transformer. Most o f the time it will have to be dipped in special stripping liquid or removed by scraping it off with a knife or sandpaper. It can also be removed by burning it off with a match , but with small wire , the wire will probably burn before the insulation.
The colors of the wire only mean there are 3 seperate windings and have nothing in general to do with the voltage. You will have to find the maker of the transformer and see what they used the colors for. In the days of tube radios, the green was usaully 6.3 volts , the red was for the high voltage (again voltage by the maker) , yellow was 5 volts, the black was for the primary voltage. Again even that was not 100% all the time.
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Nope. There are no standards for that, only suggestions as to possible colors.
http://tritium.fis.unb.br/Fis3Exp/fcim.csdc.com/fcimis/compid/ind/transfor.html
and many more.
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If you are lucky, you might be able to burn off the insulation, try a hot iron/soldering gun, and use plenty of flux (NOT ACID FLUX). A delicate hand is required if you try to remove the insulation by scraping. Sometimes you can get the solder to stick to the end of the actual wire, that is a minimal connection, but if the wire is very short it is better than nothing.
H. R. (Bob) Hofmann
mm wrote:

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No, if you could burn the enamel off you still have residue on the wire. Do you want to solder dirty wires? Use sandpaper or fine steel wool down to shiny clean copper - works for me.

contact area with the iron tip) and a little pull could break it. But its done all the time. Clean and tin the tip of the iron would help in heat transfer. Another thing you could do if the wire is too short to work with is pigtail in another larger gage wire - twist together and than you could solder much easier, heat shrink and solder the other end of the pigtail to the terminal.
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they make a chemical stripper to strip off wire enamel. I know its sold at Radio Shack (or used to be sold). DOn't know if an ace hardware would carry it.
Transformers can get really hot in their cores. I have never seen one that used burnable enamal. The burnable stuff is usually used for small inductors that get dipped into a solder pot. THe solder is hot enough to burn right thru the enamal and they don;t have to have an extra process step to remove it.

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mm wrote:

overheating enamel insulated magnet wire never makes it solderable. Just destroys it's insulating qualities. On fine wire, use a thumbs worth of fine steel wool. Poke the enameled wire into it, squeeze lightly and pull the wire out. Repeat (rotate wire a little) until the end is shinny copper. Practice with different sizes until you get the squeeze pressure down, before taking on the real repair.
There is magnet wire manufactured with synthetic insulation, that can be heated and soldered in one step. Some trade names were Nyleze, Soldereze etc. These are almost always bright color insulations, red, green, blue, and yellow are common. If you touch a hot soldering iron to it, the insulation will form small beads that will move along the wire, away from the iron tip.
One caution, a lot of shop appliance motors (drills, hedge trimmers, weed eaters) use insulated ALUMINUM magnet wire! No matter how well you remove the enamel, the wire looks "tinned" and just won't solder. You will also see only small brass crimps used to connect to this stuff.
Many manufacturers offer reasonably priced replacement transformers. I also wonder why you have so many failures? I have on occasion "unwound" a bad (internal short) transformer, removing the "lams", counted the turns. Then gauged the wire sizes and rewound the coil and relaminated the stack. It's getting difficult to find small quantities of numbered magnet wire, the papers, and electrical varnish these days. The only high tech tools? Micrometer, wire standards, and an oven. Kitchen type works fine if the "boss" isn't home ;-)
-larry / dallas
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Thanks for all the valuable, interesting information. I'll remember it.

Me? In the last 10 years or more, I have only had this one failure of a transformer. I have failures in general because I look for them. I pick up broken things to fix them. They are usually broken before I get them. Often my friends save them for me, or I get them out of the trash or at yard sales. It's a hobby. Often I give them away after they are fixed, or give them to Goodwill.
One time in NY, on my to the car on a Sunday I found a tv in the trash. I had a date -- we went to the zoo and to dinner -- but I looked forward to working on the tv when I got home. Sadly, it worked fine.

Interesting.
When I was about 12 to 14 I unwound a broken motor from an erector set. We couldn't afford an erector set with an electric motor, only the one with the spring motor, but a friend gave me his broken electric one. I unwound the enameled wire and found that it was broken at every 2nd corner or maybe every turn. I scratched the enamel off of both ends of every piece, hooked them together, and wrapped it up again. Then I made the mistake of wrapping it in electric tape instead of plain cloth. It worked but as it got hot, it started to melt the adhesive and started to smell or smoke. Maybe it was getting too hot too fast, because the wire was shorter than it had been and partially shorted, but anyhow, I figured if I tried to take off the tape, too much adhesive would stick anyhow.
And I don't think we could afford to buy me a roll of enameled wire. Nor did I know any place that sold such stuff.
Anyhow, getting there is more fun than having a motor. I did my best, even if I failed. I wasnt' upset.

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