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UK to US Transformers in reverse

UK to US Transformers in reverse

Old Oct 3rd 2009, 6:22 pm
  #1  
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Default UK to US Transformers in reverse

Hi,

Just wondering if anyone has tried using a UK builders type (240v to 110v) transformer in reverse.

From what I can gather they're only a box full of windings so in theory you could use this to power UK electrical items from US power sources, assuming that there isn't a diode in there.

I understand that the hertz rating can be different (50/60hz) and I'm pretty sure that the things most likely to complain are electrical motors but I think it's probably worth the gamble since I already have one

Any thoughts or considerations?
Regards
Nick
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Old Oct 3rd 2009, 6:26 pm
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Default Re: UK to US Transformers in reverse

Originally Posted by dirtbike View Post
Any thoughts or considerations?
Not the sort of thing you'd want to build, test for 5 mins, then hide under the sofa. If it works, leave it in the open for a good while working under heavy load conditions and monitor the heat output.
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Old Oct 3rd 2009, 6:31 pm
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Default Re: UK to US Transformers in reverse

Yeah I think thats sound advice...

It's quite a large transformer 3kva rating so assuming that it actually works (there isn't any kind of diode or short circuit protection etc..) it should be over kill for anything I'd be using it for.

I'm hoping to bring my workshop tools with me rather than have to replace them all.

Nick
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Old Oct 3rd 2009, 8:24 pm
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Default Re: UK to US Transformers in reverse

Originally Posted by dirtbike View Post
Hi,

Just wondering if anyone has tried using a UK builders type (240v to 110v) transformer in reverse.

From what I can gather they're only a box full of windings so in theory you could use this to power UK electrical items from US power sources, assuming that there isn't a diode in there.

I understand that the hertz rating can be different (50/60hz) and I'm pretty sure that the things most likely to complain are electrical motors but I think it's probably worth the gamble since I already have one

Any thoughts or considerations?
Regards
Nick
There should be no reason why that wouldn't work.
Do you know if it's an isolating transformer or an auto-transformer? If it's the latter, just bear in mind that it doesn't provide any isolation from the mains supply.
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Old Oct 4th 2009, 3:34 pm
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Default Re: UK to US Transformers in reverse

Using a transformer designed for 50Hz in a 60Hz country will actually run it cooler.

The isolation issue is worth looking into. Typically a site transformer will have a 230v winding on the primary side, and a center-tapped 55-0-55 winding on the secondary side. The center-tap of the output winding is connected to ground (and the metal case).

The neutral of your US 110V mains is also connected to ground, so if used unmodified you'll effectively short out one half of the secondary. The core would saturate, it would draw a lot of current and probably blow fuses. You can fix this by opening up the casing and disconnecting the center tap. Do be sure to leave the case grounded for safety.

It's really not too big of a job but if you have no electrical experience you might want to either get someone to check your work, or just buy a regular stepup transformer.

Check that your tools will work ok on 60Hz. If they use universal motors, they should do.
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Old Oct 5th 2009, 11:32 am
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Default Re: UK to US Transformers in reverse

And watch those dilithium crystals, they caenna take much more...
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