220 V table saws and ground

No, 75 or 100W is still 75 or 100W...

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Reply to
dpb
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As said or implied by others, the variable voltage output is good for setting up the voltage at the load, but not something that would be adjusted except as the load changes. For instance, if there's a transformer on a pole leading to a farm or ranch with 2 miles of run, the the variable feature would allow for line loss over that distance and the supplied voltage would be set to give

115-120 vac at the typical load. Good feature.
Reply to
Nonny

If a 100W bulb is run on less than its nominal voltage it will consume a little less power and run less efficiently that's all. The light will be yellower but its life will be extended. If that is the choice you wish to make then that's entirely your affair and no one else's.

Reply to
Stuart

Correct the bulbs resistance is fixed, increased voltage causes more amperage, reduced voltage reduces the amperage. Light output and bulb life will vary according to their ratings.

Reply to
FrozenNorth

If he's using 130v bulbs on 120v then he's using about 15% less KWH than he would be using 120v of the same nominal wattage. If that gives him enough light then he's got no problem. If he has to add bulbs or go up a wattage level to get the illumination level he needs then things get more complicated.

Reply to
J. Clarke

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Actually the load, in this case 100 watts, remains the same, but the lumen out decreases with increase in voltage rating of the lamp.

I used to make a very good living designing and selling industrial lighting systems.

As power costs increase the effiency of lamps becomes more and more important.

It was a straight forward process, based on total cost of ownership, to justify $30.00 lamps with 20,000 hour lamp life when power costs were less than $0.03/KWH.

With today's power costs, it's a slam dunk.

Lew

Reply to
Lew Hodgett

If you have a light fixture that's difficult to reach, Radio Shack is your friend. Our great room had a couple track lights well over 30' from the floor and a ceiling fan's 4 lights were around

25' high. Even with my straight ladder braced against the ceiling, it was awkward as the dickens getting the ladder inside, extended and within reach of either track OR the fan in particular. Eventually, some of the track bulbs departed and a couple of the fan bulbs as well. It was about time to paint the room, so I had the painter replace all bulbs with new.

I then visited Radio Shack and bought some 5a diodes for about a dime each. It was simple to install the diodes in series with the light switch, working on the floor at the switch and not up on a ladder. Each diode was well within the range of ampacity of the fixture/lights, of course.

The resulting lamps had a slightly yellower glow to them, but I never had to worry about replacing another bulb. (No diode on the fan's fan circuit, of course).

Another comment, about two lamps in a pump house wired in series, reminded me of our porch lights. There, we had a carriage light on either side of our entry doors on the front porch. The glass in the carriage lights was bubbled and cross hatched by design. I never really liked the way it looked when lighted, so I got a couple bulbs with spiral "flame type" indentations in them. They're quite common at any hardware, light or big box store. I then wired the two lights in series, rather than parallel, dropping the voltage across the two matched bulbs by 50%. The resulting light was a beautiful yellowish glow and the combined effect of the cross hatched glass in the fixtures, coupled with the spiral indentations in the bulb gave a flickering effect to the lights when someone walked or drove in front of them. It really looked swell and I soon began just leaving them on

24/7/365. When we moved from the house to another, we took the porch carriage lights with us; the bulbs were 13 years old by then, and they lasted another 10 years at the second location in the same fixtures.
Reply to
Nonny

They are called 'swinging transformers' - like swinging chokes.

The contact sets make before break - creating a shorted turn(s) that causes a little change in state. If the contacts get pitted, then all sorts of great voltage spiking occurs. That is when you call the power company and state that when the a.m. stoves turn on or afternoon heat forced air on - and it goes crazy - they know what to look for. In their load station yard.

We had one get so bad that by the time I returned from overseas it had almost eaten itself up. I put a drantz (IIRC) meter on it to measure the spikes and gave the tape to the power company. A new transformer was hauled in. It had eaten most of the sliding contact off and made it non-repairable.

Some smaller co-ops up the voltage so when a brown out occurs it isn't out of spec - just below normal.

Mart>

Reply to
Martin H. Eastburn

============================================== NOT!!!

As the voltage rating of a specific wattage lamp rating increases, so does the resistance of the filament.

This increased filament resistance provides a mechanically heavier wire which then allows for a "rough service" or "traffic signal" lamp rating.

The increased filament resistance also reduces the current flowing thru the filament which in turn reduces the lumen output.

Basic data available in any lamp catalog.

Just some of the basic engineering trade offs the lamp designer faces.

Lew

Reply to
Lew Hodgett

------------------------------------- NOT!

100 watts is 100 watts regardless the voltage rating of the lamp.

The current flowing thru the lamp is reduced which reduces lumen output when the voltage rating of the lamp is increased.

(E = I*R for a resistance load.)

Lew

Reply to
Lew Hodgett

On Thu, 10 Dec 2009 13:06:56 -0800, the infamous "CW" scrawled the following:

What used to happen is that they'd set it up, check it later, and adjust it if necessary before leaving for the lifefime of the xfmr. ;) "Highest voltage = X, Lowest voltage = Y, we'll set taps for the average of those and that's what y'all get, forever." 120v +-5%, right?

-- To know what you prefer instead of humbly saying Amen to what the world tells you you ought to prefer, is to have kept your soul alive. -- Robert Louis Stevenson

Reply to
Larry Jaques

If you have visions of becoming an electrical engineer, don't quit your day job.

For a resistive load P=E^2/R. If the lamp is rated for 100 watts at 130 volts then it will dissipate (120^2/130^2)*100 watts at 120v or about 85 watts if its resistance remains constant.

Reply to
J. Clarke

And yet you don't know how to rerate an incandescent bulb. Just goes to show that he who has the best line of bullshit wins.

Reply to
J. Clarke

On Thu, 10 Dec 2009 16:55:34 -0600, the infamous dpb scrawled the following:

Newp. I get 100W worth of light out of $2 (delivered) 23W CFLs. No replacements necessary for 2 years now, but all my Feit CFLs have failed in under a year, including the 4 they replaced at their cost.

-- To know what you prefer instead of humbly saying Amen to what the world tells you you ought to prefer, is to have kept your soul alive. -- Robert Louis Stevenson

Reply to
Larry Jaques

I use the same rating bulbs, yes. It is "nominal" 120V of course, but generally we will be closer to 125-127V than 120V and on rural lines w/ long distances fluctuations and interruptions are more frequent than most are used to; just goes w/ the territory of having only

1-and-a-fraction loads/mile on distribution lines as opposed to residential distribution grids. Hence, the lifetime is greatly extended.

Interesting that Lew would point this out in a followup post that a higher-cost bulb pays for itself even at lower power cost but can't help but try to make a putdown to the logic of using a 130V to obtain the same benefit.

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Reply to
dpb

At a typical 18-20 lumens/watt and 1,000 hour life, incandescent lamps are never even a consideration for a low cost of ownership lighting system.

Longer life incandescent lamps are purely for convenience except traffic signal lamps where the cost of servicing a signal enters the ownership cost equation.

Lew

Reply to
Lew Hodgett

After you have had a chance to review a lamp catalog, get back to me.

Lew

Reply to
Lew Hodgett

We bought a new house once and the contractor put in 130v bulbs. Not he 115v ones we buy in the store - and run them on 120 or 125v.

Anyway - when we sold the house 11 years later we still had some of the original bulbs.

Consider : P=E*I If E drops - the power drops. The bulb runs cooler. P=E^2/R or R = E^2/P 130*130/100 = 13*13 = 269 ohms hot. (rule of thumb 1/10 of hot = cold resistance or 27 ohms for surges). I=P/E = 100/130 = .76 amps Now - using the 130 bulb with 269 ohm filament and we run it at 120 :

P (used) = 120*120/269 or 14400/269 = 53.53 watts. P=E*I so I=P/E I = 53/120 = .44 amps

lower used wattage, longer life due to the derrating.

Mart> J. Clarke wrote:

Reply to
Martin H. Eastburn

--------------------------------------------- Review lamp data found in any lamp catalog.

The proof is left to the student.

Lew

Reply to
Lew Hodgett

And what do you believe that a lamp catalog will tell me? If you think that it will tell me tht a lamp rated for 100 watts at 130 volts will draw 100 watts at 120 volts then you need to take remedial reading.

Reply to
J. Clarke

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