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Discuss Can my step-up/down transformer be repaired? in the Electrical Appliances Forum area at ElectriciansForums.net

Marvo

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Must admit I assumed it was an electronic converter, but perhaps not. In that case I wonder what went bang?


You might be right, I was just going on the weight which is only one step up from blind guesswork. It sounds from the OP that whatever did go wrong was failing over time and causing occasional tripping before it eventually went big badda boom. From experience things semiconductor have more of a tendancy to go pop one-time without warning, things wirewound might be more prone to deterioration over time but again no proof.
 
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Honestly I think the wiring in the house is to blame probably. Before the transformer arrived the circuits in the house did trip a few times with normal appliances. With the transformer, though, it was every single time I plugged it in.
Given that, really hope one of you can recommend how I can protect a new transformer from the same fate.
Thanks a million.
 

pc1966

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According to the Amazon listing that thing is about 8 kilos so I'm guessing it's a wire wound step down transformer inside rather than a switch mode type supply.
Good point - I was basing it on the visual size. Even so, at that sort of new price I would doubt that you could get it rewound economically.
 

pc1966

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As to why the transformer went bang - it could just be a duff component in it, or sometimes it is provoked by a spider or similar shorting stuff out and causing an arc (which is the high current bit that does the damage, the spider is long gone by then).

You mention the house electric tripping, that is something to have investigated as it might just be a serious issue. Do you know if it was the MCB (over current) breaker that trips, or the RCD (earth leakage) one?

Transformers do draw a high inrush current so can trip MCBs and thinking about it if that really is a 5kVA transformer it would need a dedicated supply and not a 13A plug! Basically 5kVA is about 22A for 230V and usually you would be looking at something like a 32A D-curve MCB or BS88 fuse for it.
 

pc1966

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OK I looked at the device again and it is not a 5kVA transformer, the continuous load is 1500W so weasle wording from the advertisers once more:

"This model has up to 3000 Watt Maximum Capacity (110/120V <> 220/240V) with super-quiet performance.

MAX - 5000 Watt for 30 Mins Use. For continuous use: 1500W. Make sure you multiply x2 the wattage of your item and get a transformer bigger than that"


So it can be used from a 13A plug and is probably OK for a ring final that has the usual 32A B-curve MCB on it, but it is hard to say for sure if it would be trip-prone on inrush current. Just noticed you are in Ireland, maybe if in ROI your house has more radials with 20A MCBs? They would be trip-prone here. Perhaps @Risteard or @Edmond Noonan might have some insight on this aspect.

I would get a professional electrician in to take a look at your house electrics just in case.
 

Lucien Nunes

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It's too heavy to be electronic and too light to be 5kVA. It's probably a cheap nasty wirewound autotransformer rated lower than even their lowest claim, knowing that in domestic use it might not see any heavy loads. They specifically warn you against using it to supply heating loads, but most domestic loads >1kVA are heating loads. You can't get 5kVA out of it using one 13A socket at 230V or two 15A sockets at 115V anyway. In step-up mode, how you are supposed to feed it 5kVA via one 15A 115V plug even for half an hour is a mystery.

Cheap, nasty transformers that skimp on iron are also more likely to trip breakers on inrush, because they saturate magnetically for a longer fraction of the mains cycle. It's probably also wound for 220V and starts losing its spring at 240 anyhow. I would fully expect something like this to be prone to tripping a B-type MCB. A professional grade item would be more like £500 and weigh 25kg+.
 
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Maybe buy a "Local" replacement of 1 of the heaviest wattage appliances with one .. so the transformer has less work to do.

Big motor appliances cause start-up surges that may -eat into the life-expectancy of a replacement.

Larger continuous heating applinces cause gradual overheating build-ups.

Just a strategy thought. Good Luck.
 
Thanks a million everyone, this is all really good. Though I'm afraid I'm a total novice so had some trouble understanding some of the more complex advice...

I think the wiring in the house definitely needs to be looked at, but this is an "as is" rental so that rules that out.

In terms of appliances, in fact the transformer alone -- without any appliances connected -- trips the circuit.
*Given that, any specific ideas about what I could do, if anything, to protect a new (cheap) transformer?*

Planning on getting a UK "3kVA" one of the same type.

When the appliances are plugged in, generally what I have is a high-end coffee maker that is heating and in use for a total of about 10 minutes, 2 or 3 times a day. I have quite a few other appliances I use with it occasionally but the coffee maker is the only consistent one and is basically the reason I bought the transformer in the first place.
 

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