I don't think this is correct.
Power = V^2/R
Based on that, to keep wattage constant resistance must increase as the square of the voltage. Double the voltage and the resistance has to increase by a factor of four.
Chris
Funny, in the business we always called them tap changers, as did the power companies that we dealt with (nation wide in the U.S.and parts of Canada). When dealing with the manufacturers, they called them tap changers too. Glad you straitened that out. We must have been wrong all these years. I'll have to let them know.
I don't "assume" anything about "exactly" anything re: the light output. It puts out what it puts out and that's adequate w/ a 130V bulb just as it is w/ a 120V of the same wattage even though it would be somewhat more w/ the latter. _IF_ it weren't, I'd have to either bump in size or go back to 120V or add another light. I'm simply saying given the lights we have and our habits _we've_ not seen any necessity to do any of the above.
OTOH, you're the one that apparently is obsessed w/ somebody not doing as you would do and measuring lumens to the nth degree.
Under the above scenario, it's cheaper as the power dissipated will be less for the 130V bulb at something under 130V average than it will for the same rated 120V bulb at the same average >120V. Add onto that the much longer lifetime and it's "win-win".
Again, if you want to do something different; fine. Just don't claim I'm spending more in absolute $$ running 130V bulbs of the same size and you certainly aren't in position to state I don't have adequate lighting near my easy chair or not to meet my needs.
Finis, you can tilt at light bulbs all you want, I'm done here.
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Because the difference in a 60W @120V wouldn't be enough for a location that has a 100W in it, either. The substitution is as earlier stated--simply 130V of whatever I'd use 120V in that location and I'm good to go.
No, you're simply trying to make an argument that doesn't hold by making a false requirement that isn't pertinent. IOW, the strawman argument; if you change the groundrules to suit your purposes you can "win" but it doesn't negate the conclusions of the original premise at all.
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Yes. assuming the same length, material, etc.
No. The resistance should be 169 ohms at 130 volts. You seem to have gotten 156 ohms by dividing 120 volts by 0.768231 amps. There is no justification for this. The resistance of the filament will vary with its temperature. It will be lower than 169 ohms at 120 volts. but there is no reason to assume that it will be 156 ohms.
See previous comment. You seem to have derived a result from your assumptions (you assumed the current at 120 volts is 0.769231 amps in your previous calculation).
This result is based upon an incorrect assumption that the current is
0.7629231 when the voltage is 120 volts.The power at 120 volts will be between the 85 watts (the value that would be calculated if the resistance is constant with temperature) and the 100 watts at 130 volts. Thus 92.3 watts is a reasonable guess for the power at 120 volts but you have not presented anything to prove it.
Dan
With light bulbs, the explanation is _simple_. Your assumption is in error -- "everything else" does _not_ remain unchanged.
(Note: Lew had the 'results' right, albeit with a somewhat incorrect description of the 'causation')
'Rough service' bulbs use a different composition in the filament element than normal service bulbs. It has a *much* higher resistance per unit of cross-section area, and thus *does* require a larger cross-section to get the 'appropriate' resistance for the slightly lower amperage needed for the same number of watts as the lower-voltage bulb. Note: the 'wire length' of the actual 'element' in a rough service bulb is usually much shorter (not as much 'coil') -- necessitating a higher resistance 'per unit length'; over and above the compensation for the larger cross-section.
BTW, the relationship between bulb life and applied voltage is an _eleventh_ _order_ equation -- i.e., a 5% decrease in applied voltage will result in an over 70% increase in bulb life. Note: decreasing the voltage by 5% _will_ result in a _more_than_5%_ decrease in the light output, so you _do_ end up paying 'more *per*lumen*of*light*output*'.
NOTE: the cost of the electricity to operate a 'typical' household light-bulb (25-150 watt) is generally *several*times* the cost of the bulb itself.
Hint: imagine a square copper wire of a fixed length, now double its thickness and width, _in_steel_, and explain how that is equivalent to four copper wires of the original thickness in parallel for 1/4 the resistance!
By using 130V bulbs on 120 V, he's paying *MORE*PER*LUMEN* for the electricity to operate them, vs a 120V rated bulb.
Generally people thing of a light bulb as 'a light bulb', with little regard to how much light it puts out. This leads to ill-informed decisions about the cost-effectiveness of various alternatives.
The _first_ thing one has to do, is figure out how much _light_ is needed and/or desirable, then look for the 'least cost' way of getting that amount of light. Higher wattage bulbs produce more light output _per_watt_ than low wattage ones. Thus, a few higher wattage bulbs will produce more light than an equivalent wattage of low-wattage bulbs.
The true 'cost of ownership' of light bulbs depends on the cost of the bulb, the frequency with which it has to be replaced, the 'cost' (labor, etc) in performing the replacement, _and_ the 'operating cost' (the electricity to drive it).
The cost of the electricity -- over the lifetime of the bulb -- generally swamps the cost of the bulb itself.
The frequency of replacement determines how much of a factor the 'cost of replacement' is. Depending on circumstances, this can be a 'small change' item, or it can be far more than the bulb _and_ the electricity to run it.
You are correct.
Yep.
Lew
"Yeahbut" applies.
A light bulb is _not_ a 'constant resistance' device. It takes _more_ than a _simple_ high-school physics application of Ohm's Law to get an accurate answer.
Proof: measure the 'cold' resistance of a, say, (nominal) 100 watt (@120v) lightbulb. It only a =few= -- as in _less_than_ten_ -- ohms. Which is why a light bulb draws _lots_ of power (for a very short time) when it is turned on. {Google for 'light bulb inrush current' for the gory details, if you're interested.} Incidentally, this also explains while the vast majority of bulbs burn out _when_ you turn them on.
Incandescent Lightbulbs run *HOT* -- 'white hot' (grin), in fact. This
-greatly- increases the filament resistance over what it is at 'room temperature'.
Reducing the voltage of a nominal 130v bulb to 120v will result in a _decrease_ (albeit relatively minor) in the resistance of the bulb. As a result of that change, the current flow at 120V will be _more_ than 12/13 the current flow at 130v.
Thus, a '100 watt @ 130v' bulb has a nominal operating current draw of 0.7692A at 130v. a 'hot' resistance of roughly 169 ohms.
_if_ one makes the mistake of assuming constant resistance, then at 120v the consumption would be about .7100A (120/130 * .7692A, or about 85.2watt @ 120v).
BUT, this calculation is in *error*. Because the resistance of the bulb will _decrease_ -- due to the fact that it is not running as 'hot' at 120V as it does at 130V.
The exact figures depend on _exactly_ how the bulb is constructed, but for 'typical' 130V bulbs, the power consumption will be around 88-90 watts, at
120V. (Roughly 92.3 watts is the 'absolute maximum')[[.. sneck ..]]
Substituting a standard 130V bulb for a standard 120V one probably does *NOT* pay for itself -- *IF* you need the same light output as the 120V bulb gives.
Running a bulb at lower than the 'rated' voltage, _does_ extend the life of the bulb, *BUT* the quantity of light output (the 'lumens') goes down even _faster_ than the savings in electricity. Thus the 'cost per lumen' of the eletricity is _higher_ usuwing the 130V bulb at 120v, vs the 120v bulb.
It is also a fact that the cost of electricity over the life of the bulb swamps the cost of the bulb itself.
That said, there are "much more efficient" technologies for lighting than 'incandescent', e.g. 'halogen'. These technologies have a _much_ higher lumen output _per_watt_of_power_consumed_ than conventional incandescents. Thus, you can get the same _light_ output, for far less power consumed. Amortized over the rated life of the bulb, the power savings _greatly_ exceed the cost of the 'high-priced' bulb required to achieve the savings.o
Running the _same_ technology (incandescent) in a down-graded form (130V bulb at 120V) does *not* achieve these savings. In fact, because the bulb is being operated in a 'less than optimum' (relative to _design_ criteria) manner, the cost _per_lumen_output_ is higher than the optimal operation.
Eleventh power. not 16th. a 5% decrease in voltage equates to an over 70% increase in bulb life.
Depends on what you're measuring.
"Per lumen of light output", the de-rated bulb is more expensive to operate.
If the de-rated output is 'adequate', and you're just looking at the cost of operating "a bulb", the 130V bulb does save a little (circa 10%) operating money. Plus a little more for the reduced replacement frequency. The only _real_ advantage comes if the bulb is located somewhere where it is _hard_ to change -- i.e., with a significant 'labor' cost involved in performing the replacement.
A 100 W 130V bulb operated at 120V has just about the same output as a 75W 120V bulb. It's a wash on electricity cost, balanced against the cost difference for the 130V bulbs, vs 120V ones. Plus the "convenience factor" of less frequent bulb replacement. Drawback: the 130V bulbs give off a "yellower" light than the 120V ones -- one may, or may not, notice it.
A 60W 120V bulb has somewhat more output than a 75W 130V bulb at 120V. The 120v bulb is the _clear_ winner in this case. bulb is less expensive, gives off more light, and uses less electricity. The -only- advantage to the 130V bulb is less-frequent replacement.
At lower wattages (60W@130/40W@120 and 40W@130/25W@120), the cost advantage also goes to the rated 120V bulb. Again, the -only- advantage to the 130V bulb is less-frequent replacement.
What has gone unsaid is that a yellowish bulb gives the subliminal impression of warmth. By dropping the voltage across the lamp filament, you can fool the building occupants into turning down the thermostat in the winter. This saves on heating oil, gas, coal or electricity. Thus, it's obvious: a diode or series wiring saves energy during cold weather. During the summer, just boost the voltage up a tad and they'll be turning off the A/C and putting on sweaters.
Please send all flames and men in white coats to someone else.
Electricity explained I think its time for me to explain about 220 current and why it is so different from 110 volt service. First of all, it's twice as big. Secondly, it'll shock you more. Outside of that, 220 is really two 110 volt lines coming to your house from different parts of the globe. The up and down 110 comes from the northern hemisphere, and the down and up version comes from below the equator. Without trying to get technical, it all boils down to the direction water flows when it goes down the drain. On the top of the earth, it goes clockwise, while on the bottom of the earth it goes counter clockwise. Since most electricity is made from hydro dams, the clockwise flow gives you an up and down sine wave, while the counterclockwise version gives you a down and up sine wave. Between the two, you have 220 volts, while either individual side only gives you 110 volts. This is particularly important to know when buying power tools- which side of the globe did they come from? If you get an Australian saw, for instance, it will turn backwards if connected to a US generated 110 volt source. Sure, you can buy backwards blades for it, but that is an unnecessary burden. Other appliances, like toasters cannot be converted from Australian electricity to American electricity, with horrible results. I knew one person who bought an Australian toaster by mistake and it froze the slices of bread she put in it. If you wire your shop with 220 and accidentally get two US-generated 110 volt lines run in by accident, you can get 220 by using a trick I learned from an old electrician. Just put each source into its own fuse box and then turn one of the boxes upside down. That'll invert one of the two up and down sine waves to down and up, giving you 220. DO NOT just turn the box sideways, since that'll give you 165 volts and you'll be limited to just using Canadian tools with it.
ROTFL! ... should be in the Anti-FAQ.
My sinuses haven't been this clear in days... wow. :-0
Robert, You know that's a bunch of bull. If you have an Australian saw and it runs backwards all you have to do is to mount the blade backwards. Sheesh.
Max
Wouldn't doubt it. I do go overboard with my wiring at times. Well, most times. But I did only run three 8's and a ground to the shop. Reading here, I probably should have gone with 6GA to be as bullet proof! :)
On Fri, 11 Dec 2009 16:40:43 -0600, the infamous snipped-for-privacy@host122.r-bonomi.com (Robert Bonomi) scrawled the following:
Why don't ALL OF YOU stop wasting electricity and get rid of the ghastly yellow lighting at the same time? CFLs are the way to go.
My electric bill last month was $18 and change. The only incans I have in the house are in the fridge, stove (no replacements available for the two previous lamps), laundry room (130v Rough Service which was here when I moved in and refuses to die), and a pair of Reveal bulbs in the security light outside.
Speaking of ghastly, CFLs define the term. Yuck! Wouldn't own one.
Get real. The reason you have an $18 bill has nothing to do with CFLs. Hell, I'd put up with CFLs if they'd run my heat pump and water heater.
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