Advice on rewiring this stepup transformer?  - Page 1
Forum section: electronics / repair

author: artvandalai
author_rank: Regular Contributor
timestamp: January 14, 2025, 06:49:41 am
content: I bought this Chinese made step up transformer to run some 220v appliances. Some of the wires were brittle and broke off. I attempted to improve some of the wiring with spade terminals and heatshrink tubing as the wires were just soldered straight to the connectors. Any advice on how to rewire the broken wires on this step up transformer? I'm unsure how to go about rewiring this to a better safe working condition.

author: XxMandragoraxX
author_rank: Contributor
timestamp: January 14, 2025, 07:30:59 am
content: Hellow, You just need to go wire by wire, making sure you know where each one is connected. It’s important to buy the same thickness of wire as the original to avoid overheating, as choosing a thinner conductor than what’s specified can cause issues. Also, I recommend taking pictures of each step of the disassembly in case you need to go back or don’t remember how it was assembled. Update if you need any help.

author: artvandalai
author_rank: Regular Contributor
timestamp: January 14, 2025, 08:11:32 am
content: The problem is that i don't know how the wires go that are connected to the windings. This is something i don't want to mess up to prevent fires or electrocution.

author: Gyro
author_rank: Super Contributor
timestamp: January 14, 2025, 10:44:24 am
content: I suspect the reason that the wires are brittle is that they are made of low quality Copper clad Aluminium rather than pure Copper. This is not solderable once the thin Copper coating has dissolved and is unreliable when crimped as it yields too easily. The classic test is to put a sample of the wire in a flame. Copper will remain untouched (apart from some tarnising) while CCA will melt.If you can't identify which wire is which, it will be very difficult, or depending on your level of experience, impossible to identify them safely. Feeding low voltage AC from a low voltage isolation transformer and measuring voltage ratios is one way.From the general construction, transformer winding insulation, grounding etc. I'm sorry to say that I don't think it will ever be safe.PS: I would certainly ditch the USB output board. The insulation of the winding for that definitely doesn't look sufficiently isolated.

author: srb1954
author_rank: Super Contributor
timestamp: January 14, 2025, 01:47:33 pm
content: Judging by some of the photos the insulation on the wires is damaged close to the transformer so it could be that the transformer was overloaded and got excessively hot. If the temperature was sufficient to melt the insulation off the connecting wires the insulation of the transformer windings may have also suffered severe damage. In which case the transformer is likely unrepairable.Before attempting to rewire the transformer it may pay to do an insulation resistance test between windings (not applicable for auto-transformers) and between the windings and the core.

author: artvandalai
author_rank: Regular Contributor
timestamp: January 14, 2025, 09:53:12 pm
content: So i should just throw it out and buy a new one? All these Chinese made step up transformers are built the same or with similar standards.

author: XxMandragoraxX
author_rank: Contributor
timestamp: January 15, 2025, 07:45:17 am
content: The coil has terminals, they usually have them. My recommendation is that you remove the transformer from the entire case, and you will notice where the wires are soldered. Just desolder them and resolder quality wires. In this picture, you can roughly understand what I mean. All the transformers I’ve encountered usually have this system.

author: Gyro
author_rank: Super Contributor
timestamp: January 15, 2025, 09:30:56 am
content: Check the photos and posts again XxMandragoraxX, the brittle wires go straight into the winding.

author: Zero999
author_rank: Super Contributor
timestamp: January 15, 2025, 09:35:30 am
content: Quote from: artvandalai on January 14, 2025, 09:53:12 pmIf it came like that, then send it back and demand a refund. It isn't your job to fix their junk. They shouldn't be allowed to get away with selling rubbish.

author: Gyro
author_rank: Super Contributor
timestamp: January 15, 2025, 11:36:58 am
content: Quote from: artvandalai on January 14, 2025, 09:53:12 pmI hate to put it in those terms, I really don't like giving up on something. Can you raise a case and get a refund?Unfortunately, while the world provides a demand for such stuff, they will keep producing ever worse rubbish (not a dig at you btw!). Ihaveseen better Chinese ones, if you try various search terms you might find some images on the forum, but I would seriously recommend getting a locally sourced (and preferably manufactured) one so that you can examine and return it easily and get the safety that you need.The one you bought screams extra gimmicks to make it look better at very little manufacturing cost - the USB port, multi-tap input voltage switch etc. Go for one that just provide the basic function, 120V in 220V or 230V out.preferably on a safe output connector (that 220V output socket is commonly known as a death socket, similar the deathadaptors due to the amount of exposed copper and is illegal in most 230V countries). As a 'private import' the responsibility transfers to you (assuming you bought from Ali etc.)[Edit: actually, I've seen worse (bigger holes)].I may be overly pessimistic, somebody else might see more opportunity for salvage but I suspect not.

author: silly sausage
author_rank: Regular Contributor
timestamp: January 17, 2025, 04:27:55 pm
content: the only safe place for that far eastern rubbish is 6 feet underground at your local landfill, It looks to be poorly made crap.