TheRadioBoard

[Dave-N2DS]

Hi gang,

On another thread in the crystal radio section, Georg asked why we
used 120 volts as our basic AC line voltage. I took it upon myself
to have a look at Google for an answer. The first link gave me a
reasonable answer.

120volts vs. 240 volts

It seems because the US was first in power development. At the time
light bulbs only worked well at the lower voltages. Lighting was a major
use of electric power at the time. By the time Europe got around to
electrifying, light bulbs that ran on higher voltages had been developed.

Thanks Georg for bringing this up. It was one of those interesting
topics that doesn't come up too often.

Best wishes,
Dave
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[XtalHWJ]

Dave,

I responded to the other thread, but you are right to move the discussion here.

Light bulb filaments were very fragile in the early days, so heavier filaments (with lower resistance) were used. To limit the power, the voltage had to be dropped.

Automobile lamp filaments see a lot of stress and vibration, so they also have to be heavy. That's one of the reasons battery voltage in cars has stayed low. There has been talk about moving up to 48 V batteries in autos, now that a lot of LED and HID lamps are used. That would reduce the weight and cost of copper wiring.

Even after light bulbs were improved, the USA elected to stay with 120 VAC as it was a reasonable compromise of insulation requirements and wire size. There was some concern that 220V would be more dangerous in terms of household accidents. Japan still uses 100V AC.

I've always been mystified about 60 Hz. here vs. 50 Hz in Europe.

Rich
_________________
Homebrew Radio ex-Silicon Valley

[wa4qal]

It might also be worth pointing out that a lot of the early electric power systems were DC, rather than the current AC (Err, that wasn't supposed to be a pun!). Edison was a big proponent of DC, while Tesla was a fan of AC. The problem is that, with a DC electrical power system, it's almost impossible to change the voltage. Thus, all of the power has to be generated and distributed at the voltage at which it will be used. Therefore, 117 Volts was a reasonable compromise. Higher voltages would cause problems for light bulbs, and even motors. Lower voltages would cause problems for distribution, and even generation.

It was only after the switch to an AC electrical system that voltages could be easily changed with a transformer, thus decoupling the generation and transmission factors from the usage factors.

Dave

[battradio]

I the US the only apliances in the home that required 220- 240 was an electric range / oven in 30's and 40's .In the 1950's central airconditioning came about and other than the rare a drill press ,lathe or aircompressor in a large home shop no other items need 240 .For comercial needs 3 phase 240/480 60 HZ is more practical .

I never could under stand why only 50 HZ power , 25 HZ is the minimum that can be used with an incancesant light buld due to flicker , double that and you have 50 HZ , go to 60 HZ and Televison pictures don't flicker like they due at 50HZ due to interlaced scaning and transformers need to be larger .
_________________


Mark

[XtalHWJ]

[wa4qal]

As for 60 Hz eliminating television flicker, note that that only applies to NTSC. In Europe and other parts of the world, the television standard is PAL, which can operate at 50 Hz.

Also, note that some people may be sensitive to even 60 Hz flicker. Some of this depends upon the individual, the total illumination level, whether the vision is the central vision or peripheral vision, and how tired the individual is (in addition to a variety of other factors).

Also, note that the flicker of incandescent lamps depends a lot on the thermal inertia of the filament. Heavy filaments tend to have more thermal inertia than thin filaments.

Plus, there's the concern with fluorescent and glow discharge lamps. There's some mitigation of this with fluorescent lamps due to phosphor persistence, although depending upon this effect to too great of an extent may adversely affect the choice of phosphors. To study phosphor persistence, look up a device called a phosphoroscope.

Dave

[battradio]

[Broesel]

[corne]

[XtalHWJ]

[Broesel]

[andrekp]

As a vague thought in support of AC over DC, a lot of people doin't really think about it, but a LOT of things use the 60 hz as a sort of timing sync internally. There's a reason that TV's refresh at the rate they do, and fans rotate at certain speeds, and things like that. Some of it matters, some of it doesn't, but it is the way it is now.

Using DC would necessitate extra circuitry, or at least slightly more complex circuitry to keep certain things in sync. It might even cause internal problems in some things if two separate DC motors had to synch with eachother... Not to mention the problem of not being able to use transformers for stepping or isolation.

We've sort of designed our electronic world to use AC, so it's not simple to switch.

All solvable problems, and not really major, but it is a thing to think about. I imagine that the move toward super fast digital electronics has changed a lot of this as well. We could run a lot of our lives on <12v DC.

That said, a lot of early home electronics could run on whatever you decided to feed it, so long as the tube filiments were fed and you didn't over-voltage it by too much.