Transformer to feed UK machine

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mattknows

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Aside from the frequency (50 to 60Hz) difference, is it possible to use a 480/240 (primary) to 120 (secondary) as a step up transformer to feed a machine in the US that was originally from the UK that takes 220 (set up for standard UK household current so that 220 is the hot, with a neutral and ground) from (US) 120? My understanding is X1 is hot, X2 neutral, then H1+H2 hot and H3+H4 as neutral.

Thanks.
 
yes. it is possible. you need a transformer that is not labeled as primary/secondary though. call the transformer mfg tech support people and ask for a suggestion. you will need to ground what becomes the secondary side.
 
petersonra said:
yes. it is possible. you need a transformer that is not labeled as primary/secondary though. call the transformer mfg tech support people and ask for a suggestion. you will need to ground what becomes the secondary side.
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Well this is the one the supplier recommended, so you're saying this one won't work period. Well shoot.

I should add that the machine requires a transformer with at least a 5kVA rating,as the machine draws 10 amps at 220.
 
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Can you feed the circuit with 1ph 240V? If you can, the transformer you are looking at could be okay. Most of this type transformers are 480/240 primary, and 240/120 secondary. Look at the name plate, see if you get lucky.

If you have to feed with 120V, or the preferred transformer is not as shown above, look for a 240/120 primary nd a 240/120 secondary. These should be readily available.
 
Yes I have also found one that can be fed 277/240/208/120 primary and 240/120 secondary. That I believe would work. Appears I had the wrong one recommended to me.
 
190923-2002 EDT

My following comments are not based on legal rules, but on how things work.

An ordinary transformer is bidirectional. Meaning power or signals can feed into either the primary or secondary. However, from a description perspective one would usually call the power input side the primary, and the output side the secondary. But. in fact in something like a transformer used in a telephone circuit you can have power flowing both ways simultaneously.

Some power transformers are rated based on turns ratio, while others are based of the voltage ratio at full load.

If a transformer is rated on turns ratio, then its output voltage at full load is lower than implied by turns ratio. This applies equally to either direction.

If a transformer is designed as a stepdown transformer. and rated based upon its full load output, then its turns ratio will be less than implied by the voltage ratio at full load. If reverse fed, then it could actually be fed from a somewhat higher voltage than its rated output. But suppose it is fed from its rated output voltage, then the induced no load voltage in the other winding will be less than implied by its original rating. And the other winding under load will be even less.

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The UK machine will not need for there to be a "neutral", it just needs for there to be 220V between the terminals. Don't ground the 220V on one side, it could be dangerous for someone in the future who will not expect that.

What kind of machine is it? the frequency difference can really bite you in the rear on some machines.
 
Depending on what's in the machine 240V 60Hz may work out better than 220V 60 Hz. Motors and transformers are inductive loads and so the time it takes for the current (and therefore the magnetic field) to build up to the full value each cycle is proportional to 1/(applied voltage). So with the shorter time of a 60 Hz cycle, it would take 60/50 = 1.2 times more voltage to get the same value of current and magnetic field as at 50 Hz. This is why a constant voltage/frequency ratio (V/f) is often used in variable frequency drives (VFDs).
1.2 x 220V = 264V but I wouldn't recommend running your machine at such a voltage because any electronics present could be damaged, and even the insulation on motors, wiring, etc. would be stressed. But taking extra measures to reduce 240V 60 Hz to 220V may not be necessary or even desirable.
But as Jraef mentioned there could be other issues with running at 60 Hz.

If the machine is intended for use in the UK, as far as I know they actually have a nominal 240V not 220V:

https://www.se.com/uk/en/faqs/FA144717/
 
mattknows said:
Aside from the frequency (50 to 60Hz) difference, is it possible to use a 480/240 (primary) to 120 (secondary) as a step up transformer to feed a machine in the US that was originally from the UK that takes 220 (set up for standard UK household current so that 220 is the hot, with a neutral and ground) from (US) 120? My understanding is X1 is hot, X2 neutral, then H1+H2 hot and H3+H4 as neutral.

Thanks.
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UK nominal domestic voltage is 230V, not 220V. That said, it was 240V and it was changed to 230V to "harmonise" with other EU countries. In effect, nothing actually changed. Except tolerances.
 
I think there are about 3 different discussions going on here.

1) having a grounded conductor. As I understand residential power in the UK, it is nominally 230V, 50Hz, with one grounded circuit conductor. If you want to provide 220V (or 230V) 60Hz with a grounded circuit conductor, then you will need an isolation transformer.

2) step up vs step down transformers. As gar noted, transformers are bidirectional devices, power will flow in either direction. However some transformers are only 'listed' for use in one direction, and there are differences in design for step up vs step down use. How important these differences are is variable depending on the application.

3) buck/boost transformers. A buck/boost transformer will change voltage but will not re-derive a new 'system'. If you go from US 240V to 220V using a buck transformer, you will _not_ have a grounded circuit conductor on the ouput.

4) while UK residential power normally has a grounded circuit conductor, my understanding is that most European equipment is designed to be agnostic to this grounded conductor; it is expected that polarity will be unknown and that either conductor could be (but is not necessarily) grounded.

-Jon
 
mattknows said:
I should add that the machine requires a transformer with at least a 5kVA rating,as the machine draws 10 amps at 220.
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10A @ 220V = 2.2kVA, why the requirement for a 5kVA transformer? AKAIK, the transformer can handle any surge load that might be thrown on it as long as the constant load is w/in it's rating.

I stumbled across this, you might be interested in it, I can't recommend their products because I have no experience with them.
http://internationalconfig.com/icc6.asp?item=30255-620P
 
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winnie said:
... 3) buck/boost transformers. A buck/boost transformer will change voltage but will not re-derive a new 'system'. If you go from US 240V to 220V using a buck transformer, you will _not_ have a grounded circuit conductor on the ouput. ...
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Auto transformer is a pretty good idea. Use a 120/120 and connect as an auto transformer. That would give grounded 240V
 
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