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Old 03-07-2008, 09:15 AM   #1
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House Running Hot?


I am trying to find out what the maximum and minimums voltages I should be receiving from the power company are. After I moved into the house I noticed that my backup systems for my computers started switching on battery or on to a voltage trim mode rather frequently. So I have been monitoring my voltage and it routinely hits over 127V at the outlets furthest from the service entrance and with a good sized load. My average voltage throughout a 24 hour period is a little over 125V.
Iím concerned by this for 2 reasons. The first is that my bill is higher (if only slightly) than it should be because of higher voltage, means higher amps, means higher KW/h usage. The second thing and more important thing is the wear and tear on my electronics. I know from my experience that having higher voltage (even if only a few volts) will wear out sensitive electronics more quickly.
So my question is what should be the maximum that I should receive from the power company under normal circumstances? Thanks in advance.
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Old 03-07-2008, 09:22 AM   #2
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Higher voltage does not mean higher amps. A utility must provide a nominal voltage and it may fluxuate within specific tolerances. 125-127 is pretty darn stable.

"Sensitive electronics" rarely run on line voltage, but rather through a switched power supply whic automatically adjusts the output voltage regardless of the input voltage. (My laptop power supply runs on 100-240 volts AC)
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Old 03-07-2008, 09:35 AM   #3
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I'm curious as to how you can have higher voltage but not higher amps. Ohm's law says E/R=I so a 60W light bulb (240ohm) draws .5A at 120V, when you bump to 130V it's now going to draw .54A, which is (P=I*E) about 70W of power. Multiply that out over the whole house and it can be a significant change. I understand that switching devices like your laptop have high ranges of acceptable power input but not all electronic devices do. Most computer gear (not laptops) does not take well to things above 125V
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Old 03-07-2008, 09:54 AM   #4
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Plus or minus 10% is the standard. So 108 to 132 is good. Higher is much better than lower. Your ohms law is a little rusty. Divide the watts by the volts to find amps. 60 watts / 120 volts = .5 amps. 60 watts / 127 volts = .47 amps. The only problems I have seen with my voltage running around 125 is with cheap light bulbs. Everything else loves it. I have a 6 computer lan running in the house with no problems at all. Feel lucky you have the higher voltage.
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Old 03-07-2008, 10:01 AM   #5
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60 watts / 120 volts = .5 amps. 60 watts / 127 volts = .47 amps.
it's negligible, but the 60W is only at 120V. So you can't use that to determine current if the voltage is above or below 120V. Power is a result of the resistance of the device and the voltage applied to it. the current is also a result of the same 2 factors. Of course this is different when switching power supplies are used but the basics for resistive loads are sound.
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Old 03-07-2008, 10:50 AM   #6
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tjtsj,
Do the math for any voltage, current or wattage and the results are always consistant.
If the math does not work, one of your constants is wrong.
Do you have an multimeter. Use that for all the constants and see if the equation is correct.
Note: Be careful with amp reading with a multimeter. Check for maximum first. Usually 10 amps.
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Old 03-07-2008, 01:51 PM   #7
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Originally Posted by tjtsj View Post
my bill is higher (if only slightly) than it should be because of higher voltage, means higher amps, means higher KW/h usage.
IF anything it would be lower but never enough to notice

if your ups is going into trim at 127 I would check the settings that shouldn't happen untill you get to around 130 - 132.
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Old 03-07-2008, 04:28 PM   #8
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The power consumed by an incandescent lamp versus the voltage applied is not all that predictable because the filament resistance rises as the filament temperature rises.

The impedance of motors is also difficult to predict since the rotational speed may increase as voltage is increased resulting in a change in the reactive component of the impedance, and/or the windings may heat up resulting in a change in the resistive component of the impedance. In turn the power consumption as voltage is increased is difficult to predict. In general, on the other hand, low voltage results in overheating of motors which in turn must mean disproportionatly high current draw.
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Old 03-07-2008, 06:34 PM   #9
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Quote:
Originally Posted by jrclen View Post
Plus or minus 10% is the standard. So 108 to 132 is good. Higher is much better than lower. Your ohms law is a little rusty. Divide the watts by the volts to find amps. 60 watts / 120 volts = .5 amps. 60 watts / 127 volts = .47 amps. The only problems I have seen with my voltage running around 125 is with cheap light bulbs. Everything else loves it. I have a 6 computer lan running in the house with no problems at all. Feel lucky you have the higher voltage.
Problem with that logic is the watts is not a constant. It does change as voltage goes up and down. Neither is amps. As the filament heats up resistance changes, watts changes, and amps changes.
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Old 03-07-2008, 07:17 PM   #10
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Problem with that logic is the watts is not a constant. It does change as voltage goes up and down. Neither is amps. As the filament heats up resistance changes, watts changes, and amps changes.
That logic is plenty close enough to show that current will go down on a resistive load when voltage goes up. Incandescent lamps are a resistive load.
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