USA mains voltage.

[Geoff]

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.

 

[Michael Karas]

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.

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]

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.

 

[Martin Brown]

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.

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

 

[Phil Allison]

"Geoff"

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.

** 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

 

[Uwe Hercksen]

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.

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

 

[Phil Allison]

"Uwe Hercksen"

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.

** 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.

 

[Spehro Pefhany]

+/-5% _at the mains plug_ is very optimistic. Better to design for
+10/-15% or wider (especially momentarily on the low side).

 

[Phil Allison]

"John Fields"

A transformer designed for use in the US will have an output at least
20% less than it should, and a transformer designed for use in Japan
could blow up if used in the US.

** 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

 

[Rich Grise]

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.

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

 

[Jamie]

Really?

Jamie

 

[Geoff]

Thats the sort of info I was after. Is that USA wide? One of
the posters said his local supply drops to 98V in summer. That
would be an outlier in that case. As a lad most hobby stuff I
read about the USA stated 117V as the nominal. I know some
areas of north Japan use 100V, but that market may be non-
existant for this product and I may be able to handle that
eventuality by choosing the 100V tap only for that area. My
customer knows where his overseas customers are located.

 

[Geoff]

"Phil Allison"

"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

The transformer I have is a single multitapped one and is made
to order by SES in Melbourne. I can change it as I like but
need to make a few more batches of 10 or so to use up stock. I
will consider doing this in conjunction with choosing an inlet
selector/IEC module which does not require a rear panel
metalwork or artwork change (no small deal).

The 120V sounds like an appropriate choice. There is a fair
overhead on the secondary voltages, I might do a variac check
on the next one as a check.

 

[Phil Allison]

"John Fields"

But that's all probably moot since switching supplies level seem to be
leveling the field.

Any thoughts ?

** The Chinese and others are still making huge numbers of iron core
transformers - for small AC adaptors mostly plus toroidal and R-core
types in all sizes.

SMPSs only shine when you need regulation of the DC voltage.

My Westinghouse ( 5 yo) gas oven has 300VA auto-transformer for the SiC
igniter that only comes in 120VAC rating.

Very few audio power amps and no tube guitar amps use SMPSs.



..... Phil

 

[Geoff]

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.

A valid point but this is a low volume specialised product
with not much complexity and a reputation for reliability. The
voltage is preset to the end customers country. Plus, my
customer is paranoid about design changes and previous bad
experience with switch-mode designs.

 

[Geoff]

Is there some reason (large load, etc. ) that you can't use
a switch mode, power factor corrected power supply capable
of accepting a wide range of input voltages?

Better yet, design your product with a wall wart of lump in
the line type supply that you can source, already designed
and tested from a repotable source.

No single off the shelf switchmode will give 600V 30mA, 9V 7A,
and +/- 15V low noise.

 

[Geoff]

You can start with a PFC, universal switchmode supply to
make one or two voltages, +-15 maybe, and convert from
there. We buy a MeanWell 150 watt, UL/CE switchmode PFC
supply for about $30. We can't buy a transformer for that,
much less the line voltage tap-switch module and rectifiers
and caps that a transformer would need.

John

I agree with that philosophy where products are available.
Except in this particular case the 600V and 9V supply wil
probably add up to more than the cost of transformer+selector
switch+labour.

 

[Phil Allison]

"Geoff"

I agree with that philosophy where products are available.
Except in this particular case the 600V and 9V supply wil
probably add up to more than the cost of transformer+selector
switch+labour.

** JL is talking out his arse as usual.

For your app a custom wound tranny is ideal.

" ... 600V 30mA, 9V 7A, and +/- 15V low noise. "

You simply have 3 secondary windings done to your specs on one tranny of
about 120 VA - quite compact and light if a toroidal is used.

Efficiency of such a tranny is about 92% at full load, much better at lower
loads.

Reliability is NOT an issue at all - unlike with all SMPSs.

And BTW - PFC at such low power is a wank.




..... Phil

 

[Geoff]

"Geoff"


** JL is talking out his arse as usual.

For your app a custom wound tranny is ideal.

" ... 600V 30mA, 9V 7A, and +/- 15V low noise. "

You simply have 3 secondary windings done to your specs on
one tranny of about 120 VA - quite compact and light if a
toroidal is used.

Efficiency of such a tranny is about 92% at full load, much
better at lower loads.

Reliability is NOT an issue at all - unlike with all
SMPSs.

And BTW - PFC at such low power is a wank.




.... Phil

Exactly. It's not a toroid but nevertheless it is less than
$100, has excellent isolation and failure rate of this
manufacturer is known to be about 1 in 2000 IME. I can't do
anything about the secondary requirements. They are defined by
the load which is not modifiable. Good point about the
reliability. That is important since I would have to bear the
warrantee costs. Thanks for reading the requirements.

 

[PeterD]

Thats the sort of info I was after. Is that USA wide?

Yes, but realize that each 'drop' can vary somewhat. But the goal of the
utility company is that the customer get 120/240 volts.

One of
the posters said his local supply drops to 98V in summer.

That is *very* unusual, and I suspect that the 'customer' should contact
the local utility and see about having the pole transformer upgraded. It
is NOT acceptable to drop to under 100 volts.

That
would be an outlier in that case. As a lad most hobby stuff I
read about the USA stated 117V as the nominal.

Many years ago 115, 117, 110 and some other voltages were 'local'
standards. As the years progressed, it was realized that a national
standard was needed, and 120 was chosen.

I know some
areas of north Japan use 100V,

Yep, Japan's standard is 100 volts--the only country that I know of with
that voltage! How'd that happen? Got me!

but that market may be non-
existant for this product and I may be able to handle that
eventuality by choosing the 100V tap only for that area. My
customer knows where his overseas customers are located.

I find it difficult to imagine any electronic device that won't handle a
spread from 110 to 130 without any problems at all. If it doesn't handle
that spread then I'd call that a design flaw. Ideally you should be able
to handle 100 to 140 volts without serious impairment to functionality,
though that may be a bit idealistic.