Hi
I am making a line of products to ship to the US. Since my preferred voltage selector selector has only 3 positions, I would like to have only 1 position for the USA. Currently I have a choice of 110 volts or 120 volts. Practically, is 117 the closest nominal so I can choose 120 volts setting for the USA? It is a 50/60Hz transformer input.
120 should be fine though in some areas (where we live) the line Voltage can get as low as 98 on a hot day with all the neighbors running 6+ kW AC units. Normally it's about 122 at our house.
G=B2
Geoff pretended :
The design Nominal in the USA is 120/240 volts 60hz. That doesnt mean thats what everybody gets. In Oz the nominal is supposed to be 230 in recent times but I live under a transformer and it runs at about 240 volts most of the time.
You would do well to reconsider your design. Messing around with a voltage selector switch is not the thing to be doing in todays world with the technology that is available. Most products today use designs with efficient switching power supplies that accept a wide input range of 90 to 260 VAC at 50 or 60 Hz.
Michael Karas explained on 15/08/2011 :
Having expierenced power supply problems from 60hz 110/200 volt ?? countries over many years the new idea of design for 90/260 volt 50/60 hz seems a great way to go as far as those of us who don't live on the flat earth (USA) are concerned. Think of the out of range currents in a fan motor designed for 220 volts 60 hz running on 240 volts 50 hz because someone thought it would be OK inside a machine exported from USA.
Reconsideration of the design is not simply one of replacing the power supply. Instead it has to be a system level thing and in the case you called out the fans would typically be changed out to be low voltage DC powered fans.
Michael Karas formulated the question :
Yes, thats true but it took many years for that message to get back to the flat earth. I was just using it as an example of short sighted design.
I still remember discovering how a Ronson electric razor was actually
*supposed* to work the first time I visited the USA. It relied on a 60Hz mechanical resonance to work properly and tended to jam on a UK 50Hz supply. They were widely advertised in the UK as suitable Christmas presents for men by some nutter who bought the company.I swapped to a properly engineered Braun shaver soon afterwards.
The most extreme example I can recall was a US brand of early multisync monitor that included a small proportion that in the UK would under some unfortunate circumstances spontaneously catch fire if left on power for more than a few days at a stretch. The fault was that on some of them the flyback transformer was going into saturation on UK video refresh rates. We swapped to NEC after that and never looked back.
Regards, Martin Brown
"Geoff"
** The most common arrangement is a split primary transformer - each half rated at 120 volts and 50 Hz.Wired in parallel, it is fine for the USA and Canada.
Most of the rest of the world is then covered by the series connection - pay attention to correct phase.
Japan is the really odd one out - with a nominal AC supply of 100 volts and either 50 or 60 Hz depending on which part of the country.
.... Phil
Phil Allison schrieb:
Hello,
a transformer designed for 50 Hz will operate with 60 Hz also, so what is the problem? You only have to avoid using a transformer designed for
60 Hz only with no reserve in iron weight.Bye
"Uwe Hercksen"
** Helps if you read the whole of a post and don't snip it and forget.---------------------------------------------------------------------------
** The most common arrangement is a split primary transformer - each half rated at 120 volts and 50 Hz.Wired in parallel, it is fine for the USA and Canada.
Most of the rest of the world is then covered by the series connection - pay attention to correct phase.
Japan is the really odd one out - with a nominal AC supply of 100 volts and either 50 or 60 Hz depending on which part of the country.
---------------------------------------------------------------------------
.... Phil
+/-5% _at the mains plug_ is very optimistic. Better to design for +10/-15% or wider (especially momentarily on the low side).
"John Fields"
** The latter is not true.Japan local market products all use 50Hz rated transformers so can take an extra 20% in voltage if used at 60 Hz.
For a give level of core saturation ( Imag), input voltage and frequency are in simple proportion.
... Phil
Ignore the noise on the thread. Just stamp it 120, albeit I know you know to design it to take about 95~125V. They still call that "120."
Have Fun! Rich
Really?
Jamie
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