Electronics > Repair

Advice on rewiring this stepup transformer?

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artvandalai:
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.

XxMandragoraxX:
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.

artvandalai:
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.

Gyro:
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.

srb1954:
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.

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