Changing 120v AC to 240V

[Adrian C]

Unlikely, me thinks. 240V in the states would be used for high power items that would otherwise draw too much current at 110/120V. This class of item wouldn't fall into that use category, 240V wouldn't necessarily be plumbed in at the environment of use (studio, lounge etc...).

More than likely the choice of transformer is commonly in international use. However the designer might not have sized the device for 50Hz use, even though the provided windings are configurable. And then there's other components. Ratings of capacitors, rectifiers, EMI filters and insulation / creepage distance.

So all that needs checking to be safe. You are right about consulting documentation.

[Capitol]

As the product is described as 50/60Hz. It is very unlikely that two different transformer cores will be used. Also, 110/120V products have to withstand up to about 150V in operation because of the US distribution system of very long lines and the resulting poor regulation. I can't recall the exact voltage ranges we designed for in

120V PSUs, but I reckon it was 80 to 160V. My experience is that I've yet to see a US consumer transformer fail due to core saturaton at 50Hz. I generally buy US ceiling fans for summer use and none of these have yet shown any signs of overheating.

[Dave Plowman (News)]

Not quite sure what you mean? On an analogue power supply, the mains input is always set by tappings on the transformer.

If they were cutting costs to the last fraction of a penny on components, why use a dual winding transformer? Be cheaper to have a different one for each and every voltage? And make assembly easier?

Bit difficult, that one.

[Dave Plowman (News)]

It's pretty easy to get a 110v transformer to run US equipment here. If it really were a problem with transformer design on the average low power device I'd have thought it would be known.

[Martin Brown]

There may be jumpers that can switch it from a series to parallel winding configuration if that is what the maker intended. A lot of US stuff tends to be cheapskate though and only work on local US mains.

Ronson electric shavers spring to mind as an example of a horrible design that depended on a 60Hz mechanical resonance to work properly and was useless in the UK. They pushed them very hard as Xmas presents.

No idea if their modern ones still have this problem but they did in the

1970's.

Depends how they cost their inventory.

LCD thermochromic label and check after a few hours use.

[Dave Plowman (News)]

I'd suggest you read my first post.

[Dave Plowman (News)]

Got it done and all working. Transformer only slightly warm after running an hour or so.

[Davey]

We lived in many houses in the US, and 240 volts was only ever provided for dryers or cookers. We never had any sockets (receptacles in American) wired for 240v except for those specific devices.

[Tim Streater]

Sorry, my post was incomplete. I meant to say: " ... and a whole variety of different 120V sockets."

I had 2-pin, 2-pin-polarised, 3-pin, and I'm sure there must have been others. The US 3-pin socket and its flimsy accompanying plug is a PoS, given that for a given activity, twice the current is passing, hence four times the heat generated at the socket. The cable for anything using a lot of power, such as a fan heater, is huge.

[Davey]

Understood.

Totally agreed. And why they haven't caught on to the idea of putting a fuse in the plug, I have no idea. Most plugs there now are moulded onto the end of the cable.

[Dave Plowman (News)]

In theory, each US socket is on its own radial with its own circuit breaker.

UK fuse in the plug is to protect the flex (maximum 13 amp) as the circuit is capable of 30 amps or so.

[Capitol]

US Xmas lights have fused plugs.

[S Viemeister]

Really? Each socket on its own radial? Radials, yes. Circuit breakers, yes. But apart from things like freezers, cookers, etc, quite a few sockets per radial.

[Tim Streater]

And the notion of wiring one up yourself appears to be foreign. I had the devil's own job finding an ordinary 3-pin plug I could wire myself. And even then it was ugly as sin.

[Tim Streater]

Guess it has to be because of the potential current draw.

[Davey]

Agreed. When we had some additional wiring done, it was because the existing CB couldn't handle both the microwave oven and the 'fridge together, and that circuit supplied the whole kitchen except for the

240v oven. There was one CB for each end of the house on each floor, making 4 CBs, including one for the single room upstairs.