teddy52food
Well-known Member
I just read the post by Dave2 about electricty. I have a question. What is the actual voltage of AC power? 60 times a second it is positive. 60 times a second it is negetive & 60 times a second it is zero.???????
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- Thread starter teddy52food
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Home AC Power is 60 Hertz aka 60 cycles per second. Its in a sine wave pattern starting at 0 then rising to its positive peak then falling again to 0, then dropping down to its negative peak, then back up to 0 and this happens (completes the cycle) 60 times per second.
Got it????? Just look at a typical sine wave and configure it to 1/60 th of a second to complete one complete cycle.
John T
Got it????? Just look at a typical sine wave and configure it to 1/60 th of a second to complete one complete cycle.
John T
The actual voltage is whatever the transformer or utility sets it to be (less voltage drop) such as the typical home AC secondary nominal voltage of 120 Line to Neutral or 240 line to line. However much industrial power may be 208 or 240 or 277 or 480 volts single or three phase. YES its still at zero when it crosses zero as in the sine wave example I discussed above.
John T
John T
True, it goes positive 6o times per second and negative 60 times per second, but it is zero for a total of 120 times a second.
The 120 volts you are used to referencing is RMS value which is Root Mean Square which is the square root of the squares of all the instantaneous values of the sine wave.
True peak value of any sine wave is 1.414 times the RMS value.
So, the typical house voltage of 120 volts is the amount of AC voltage that would produce the same amount of heat in a purely resistive circuit if it were being powered by a 120 volt battery.
The actual peak to peak voltage of the household power is nowhere close to 120 volts if you would look at it with an oscilloscope.
Rather, it is 1.414 times the 120 volts it is typically called.
Likewise, RMS value is .707 times the Peak to Peak voltage.
The 120 volts you are used to referencing is RMS value which is Root Mean Square which is the square root of the squares of all the instantaneous values of the sine wave.
True peak value of any sine wave is 1.414 times the RMS value.
So, the typical house voltage of 120 volts is the amount of AC voltage that would produce the same amount of heat in a purely resistive circuit if it were being powered by a 120 volt battery.
The actual peak to peak voltage of the household power is nowhere close to 120 volts if you would look at it with an oscilloscope.
Rather, it is 1.414 times the 120 volts it is typically called.
Likewise, RMS value is .707 times the Peak to Peak voltage.
440roadrunner
Member
(quoted from post at 19:41:41 01/16/10)
Likewise, RMS value is .707 times the Peak to Peak voltage.
Nice try, but WRONG.
RMS is .707 X the PEAK that is from zero to ONE peak of a 1/2 cycle
Here's a pic
http://academic.pgcc.edu/ent/ENT%20171%20Online%20Project/rms.gif
(quoted from post at 19:41:41 01/16/10) The actual peak to peak voltage of the household power is nowhere close to 120 volts if you would look at it with an oscilloscope.
Rather, it is 1.414 times the 120 volts it is typically called.
AGAIN INCORRECT. The "actual peak to peak voltage" is TWICE that amount. 1.414 gives you the PEAK, or the amount of 1/2 cycle
You are correct on the rest. The entire reason for using the RMS figure is so that we can relate to the DC equivalent voltage for figuring power. That is to say, if you have 12V AC RMS versus a battery which is 12V DC, they will produce the same amount of power.
If on the other hand you had an AC voltage that was 12V peak---or 24V peak-to peak, the DC equivalent of that would be 12V X .707 = 8.484.
Except that Dave2 in is Germany, where he's probably getting 240VAC at 50 Hz in a delivery system that is quite different than the US system - 240V line to neutral, no second line (one hot, one neutral, transformer not center-tapped).
US single-phase distribution to households is 240V (60 hz) line to line from a center-tapped transformer with the center tap being the neutral, and the neutral being grounded at the service entrance. That gives 120V line to neutral, and limits the line to ground voltage to 120V as well.
US single-phase distribution to households is 240V (60 hz) line to line from a center-tapped transformer with the center tap being the neutral, and the neutral being grounded at the service entrance. That gives 120V line to neutral, and limits the line to ground voltage to 120V as well.
Anonymous-0
Well-known Member
Voltage can be what ever you want. What you're referring to is Hertz or cycles between positive and negative, rather than AC volts. Dave
440roadrunner
Member
(quoted from post at 23:32:24 01/16/10) Voltage can be what ever you want. What you're referring to is Hertz or cycles between positive and negative, rather than AC volts. Dave
and this one makes about the least sense of all.
Voltage can NOT be "whatever you want" the voltage is what the power company supplies, unless you have some sort of transformer to, uh, well, "transform" it.
ONE CYCLE that happens in ONE SECOND used to be known as cps or cycles per second. Some time ago, that term was dropped in favor of "Hertz." Therefore one cycle in one second is now referred to as on Hertz.
That is, (in this case) one sine wave from start to finish in one second is now "one Hertz."
So 60 Hertz power is "60 complete sine wave cycles in one second", formerly known as 60 cps or incorrectly, "60 cycles"
Anonymous-0
Well-known Member
What I was referring to is that the voltage can be anything. If you made a 50 volt AC transformer it could be 60HZ the same as if you made a 48,000 volt AC transformer. If I remember right 60HZ is actually 120 cycles. Inverters such as in welding machines have much higher hertz. On a basic AC welding machine the voltage can vary greatly from around 80 open circuit down to 24 volt while welding. It still stays at 60 HZ. Fancy TIG welders have fully adjustable wave balance and can vary the hertz and also how long on each side of zero the arc is. Dave
Anonymous-0
Well-known Member
A correction. 60HZ means the direction of flow changes 120 times, not 120 cycles. Dave
ny day above ground, I'm thinking it is positive.(quoted from post at 09:54:27 01/17/10) Is that positive or negative ground?
When I'm below it, ..........not so positive.........I reckon I won't be thinking at that point, but my grandchildren will probably think it is negative.
buickanddeere
Well-known Member
60 times a second + polarity,60 times - polarity and 120 times per second zero.
On a 120V AC circuit the sine waves peak at 171 volts.
On a 120V AC circuit the sine waves peak at 171 volts.
buickanddeere
Well-known Member
Amen, somebody here understands AC power.
As Buick-Deere stated, power from the grid is around 170 volts at the peaks and nadirs of the cycles (hi and low). The stated 120 VAC is more of an average. Most portable generators only put out 150 VAC at the peaks and nadirs, and is the reason why they don't run battery chargers properly. Most shop-type battery chargers work by clipping the 160-170 range peaks and valleys, and therefore work lousy when plugged into a genset only making 150 VAC. It' been a major issue for years with off grid people using solar, battery banks, and chargers sometimes run on gensets.
hoosier boy
Member
what I remember about electric engineerin is it was all math, never got to real wiring.
hat is because installation is the installer/technicians job, not the design engineers job. That is what tech schools teach.(quoted from post at 14:26:07 01/17/10) what I remember about electric engineerin is it was all math, never got to real wiring.
scot in pa
Member
I read somewhere that 60 Hertz is perfect for electrocuting someone, and that moving it some either direction makes it a lot less harmful.
Edison did his best dirty work to promote that idea in order to discredit Tesla & Westinghouse, but he lost.(quoted from post at 15:56:39 01/17/10) I read somewhere that 60 Hertz is perfect for electrocuting someone, and that moving it some either direction makes it a lot less harmful.
I don't know about the Edison story, but 60 cycle, 120 VAC current does tend to be more deadly than higher voltages, last I heard. I worked as a lineman back in the 70s for PSE&G, and my father did the same going back to before WWII. The majority of deaths, at least to line-workers, were from working with 120 VAC, not the high voltage three-phase lines. That because of what it does to the human electrical system that runs the heart. I'm sure some of that is also due the workers being a little less careful when working with low voltage, especially with two bare hands that makes a perfect path through the heart.
120 VAC, along with the inherent resistance of human skin, creates the perfect 120 mAs of current flow through the body to put the heart into fibrillation.
With high voltage, 10 amps will burn something awful, and 20 amps can blow off an arm, leg, or whatever. I've known a few people that got pieces blown off from three-phase high-lines and survived.
120 VAC, along with the inherent resistance of human skin, creates the perfect 120 mAs of current flow through the body to put the heart into fibrillation.
With high voltage, 10 amps will burn something awful, and 20 amps can blow off an arm, leg, or whatever. I've known a few people that got pieces blown off from three-phase high-lines and survived.
less care with "just little old 120v" is as you touched on is likely a giant factor. It only takes those few milliamps thru the heart to stop it from functioning correctly.
If you get the electrodes to the right spot on the brain, a 1.5 volt AA battery will put your lights out permanently.
If you get the electrodes to the right spot on the brain, a 1.5 volt AA battery will put your lights out permanently.
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