Transformer secondary wire repair help - Page 1
Forum section: electronics / beginners

author: akabek
author_rank: Contributor
timestamp: January 19, 2023, 05:39:30 pm
content: I am assembling the Thaikit CH-012 Transistor Curve Tracer. I ordered and received a transformer with secondary 15v-0v-15v outputs. When I opened the box one of the 15v wires was loose. I could feel the transformer was loose in the box before opening it so the wire must have broke off during shipping. Can I repair this? It looks like it would need to be taken apart to get to the broken wire.

author: inse
author_rank: Super Contributor
timestamp: January 19, 2023, 06:03:12 pm
content: This kind of transformer is hardly worth the effort.Complain about negligent packing at the supplier.Get a new one for a few bucks.

author: akabek
author_rank: Contributor
timestamp: January 19, 2023, 06:07:28 pm
content: They are shipping me a new one but I was wondering if I could salvage this one.

author: Gyro
author_rank: Super Contributor
timestamp: January 19, 2023, 06:55:14 pm
content: As it is a split bobbin transformer, there is no particular issue with mains isolation as long as you don't disturb the insulation on the primary.There are a couple of options that you could maybe try...1. As the bare strands of the 'flexible' lead are still visible, you could maybe just tin the ends and solder on another lead, securing it mechanically. Worst case the soldering heat could cause a secondary shorted turn, but you could test initially with a dim bulb test on the primary and appropriate fusing.2. Keep it as a single 15V secondary transformer (of aproximately half the VA rating).3. More difficult. Remove the outer tape on the secondary and re-terminate the end of the wiring - assuming that it is the outer turn rather the burried inner. More difficult because the transformer is vacuum impregnated so you can't just unwrap the tape. [EDIT: I can't see all three leads, but it looks as if it is the inner end of the winding].4. Remove the secondary winding completely by more brutal mechanical means, again being very careful not to damage the primary insulation in any way, and re-wind it with another low voltage secondary of your choosing for another project. Do this by threading the wire rather than dismantling the core - more tedious but will result in a better, quieter result.As inse said, it's not worth expending a lot of effort on it, but it could be useful if you need a non-standard voltage in future.

author: akabek
author_rank: Contributor
timestamp: January 19, 2023, 10:01:28 pm
content: Thanks for the responses. I will wait for the new one to show up and put this one aside.

author: BillyO
author_rank: Super Contributor
timestamp: January 20, 2023, 01:12:25 am
content: Quote from: inse on January 19, 2023, 06:03:12 pmThings in Germany might be different, but I doubt it. It's more likely you have not bought a power transformer recently.1) This is a nice transformer. Fantastic primary-secondary isolation.2) Transformers are as expensive a f#ck these days. I just bought 4 Triad FD6-24 (24V 30VA) transformers for a up-coming series of projects. They were over $25 USD each!!I can totally understand the OPs desire to fix it.

author: Nusa
author_rank: Super Contributor
timestamp: January 20, 2023, 01:21:23 am
content: I'd remove the outer tape just to get a better look at the situation before deciding if it's worth the effort.

author: Psi
author_rank: Super Contributor
timestamp: January 20, 2023, 01:22:46 am
content: It likely is fixable yes, the wire that's broken is probably soldered/joint to the enameled transformer wire under the yellow insulation.So if you can remove the yellow insulation you might be able to solder on a new wire and put some new insulation on.Should be pretty safe to do if you can leave the primary mains winding intact.Given the core bobbin design, it looks like the mains side is totally separate?So you can likely remove the 15V yellow insulation without touching the primary side.I would say 95% chance that is easily fixable for anyone with some skill using a soldering iron.