[GreenKeys] History - Why voltages and frequencies are chosen(5v & 3.3v l...

[Sheldon Daitch]

I've got a guess or two on why the double voltage relationship.

As noted in the discussion, the US "standard" for most end users, 120/240, so that the 
user can have the higher voltage for larger loads, big air conditioners, stoves, dryers
and similar and have the two 120 legs against neutral for smaller loads.  

Was it possible that many other countries viewed the US use of 240 for some 
loads and decided to simply standardize on 240 for their single phase loads,
to reduce copper requirements in structures.

Also, in the days before switching power supplies, it was easy to market 
dual voltage products with dual primary and equal windings in the power transformer,
to operate equipment in both regions 120 vs 240, without major changes in the
transformer.  The primary windings in phase and in parallel for 120, in phase
and in series for 240 operation.

With that said, however, I can remember that years back, much of the consumer electionic
equipment made in Japan for the US market was for120 only while there was also a
world a market unit which had a voltage selector on the rear panel.  I am thinking there
might have been some reguatory issue with dual voltage equipment sold in the US markets,
but that no doubt has changed, as I started seeing more and more equipment with 
selector switches.

These days, with switching power supplies, so much equipment works fine from 100VAC
to 240VAC.  Even so, I remember some Scientific Atlanta rack mounted satellite receivers
which were marked for the US market as 120VAC units, but really had 100-240 VAC 
capable power supplies and we were told it was either a UL or NEC issue years back.

Sheldon and his random thoughts and guesses.




________________________________________
From: greenkeys-bounces at mailman.qth.net [greenkeys-bounces at mailman.qth.net] on behalf of Keith Mc [acti at provide.net]
Sent: Sunday, November 25, 2012 5:17 PM
To: Greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] History - Why voltages and frequencies are chosen(5v & 3.3v l...

... and why did many places choose (roughly) TWICE the voltage,
for mains?  You don't see "1.5x" the voltage, so could there be
some physical or design property involved in the number selection?

- Keith Mc.