60 Hz AC system, change in direction of current

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Alchemy One

Joined Oct 5, 2019
89
How many times the direction of current change in one second in our so-called 60 Hz AC system?
Everybody seems to say it is 60 times a second.
I think it is false. What am I missing?
 
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Jony130

Joined Feb 17, 2009
4,975
Wee see this:
prąd.PNG

And each half of a cycle will last 1/120Hz8.4ms and the whole cycle (two half) will last 1/60Hz ≈ 16.7ms
 

AlbertHall

Joined Jun 4, 2014
8,364
During one full cycle, the current direction will change from 'positive' to 'negative' and back again to 'positive so the current will change direction each half cycle, thus 120Hz.
 

Reloadron

Joined Jan 15, 2015
4,508
I think it is false. What am I missing?
My scope says that my 60 Hz house current (when there is a load) changes direction 60 times per second, my frequency counter seems to agree with that so I have to agree with the consensus.

I also read this on the Internet:
"An alternating current will flip the direction of charge flow (60 times a second in North America (60 Hz) and 50 times a second in Europe (50 Hz)). This is usually caused by a sinusoidally varying current and voltage that reverses directions, creating a periodic back and forth motion for the current".

It's pretty common knowledge that they can't put stuff on the Internet unless it is true so it must be true. I also read that on the Internet.

I think it is false. What am I missing?
Maybe this would go better if you explained, in detail why you think this is false rather than have everyone else state why they feel it is true. This way people would better understand your exact, well defined, thinking on the frequency of AC current.

Ron
 

ElectricSpidey

Joined Dec 2, 2017
690
If the change at the beginning of each cycle counts, then it changes twice per cycle.

If you isolate each cycle, then it only changes once. (assuming the start at zero crossing)
 

Tonyr1084

Joined Sep 24, 2015
3,578
In 60 cycles, one cycle consists of a complete waveform. Starting at zero - first it goes to the (lest assume) positive peak, then it goes to the negative peak then returns to zero. That's one cycle. During that one cycle the current starts out going (again lets assume) positive, then it changes direction and goes negative, crosses the zero point, goes to the negative most part of the period, then changes direction again and returns in a positive direction to the starting point. One single cycle. During that one cycle it changed direction twice. So yes, the current changes 120 times during a 60 cycle period.

But this depends on where you start the counting. I'm starting at zero. You could start anywhere in the cycle, just be sure to count a full period. If you start at the negative point in the waveform, from there current is moving in the positive direction. Once it reaches the positive point in the waveform it changes direction (once) and heads back toward the negative point. In that instance current has changed direction only once. However, current must again change to go in the positive direction. But generally, we assume the process has been going on since before we started counting, and we always start counting at the zero crossing point.
 
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AlbertHall

Joined Jun 4, 2014
8,364
In the diagram below, the blue arrows mark the start and end of one cycle of an AC waveform. The pink arrows mark the changes of direction. There are two changes of direction in each cycle.
prąd.jpg
 

Tonyr1084

Joined Sep 24, 2015
3,578
If the change at the beginning of each cycle counts, then it changes twice per cycle.

If you isolate each cycle, then it only changes once. (assuming the start at zero crossing)
If you start at the zero crossing then you must return to the zero crossing. Starts positive, changes to negative, then changes back to positive until it reaches the zero crossing again. Remember, a cycle is a complete 360 degree movement.

{comment removed due to inaccuracy of statement}
 
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Exactly, if you start the count at the peak of a cycle it must change twice to return to that peak.

No, Tony if you start at zero crossing, and count only one cycle there is only one direction change.
 

Tonyr1084

Joined Sep 24, 2015
3,578
@ElectricSpidey You've got me rethinking this entire thing now.

[edit] During the positive period of the waveform current is moving positive (conventional current). That's half cycle. During the negative period of the waveform current is moving negative. That constitutes a single change in direction. However, during the next positive waveform the current has changed direction again. So you're starting out with a change in direction. All positive peaks are odd numbers in the count and all negative peaks are even numbers in the count. I'm standing on 120 changes per 60 Hz.
 
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AlbertHall

Joined Jun 4, 2014
8,364
No, Tony if you start at zero crossing, and count only one cycle there is only one direction change.
The zero crossing point is a point of direction change. So if you go from that point to the end of the full cycle there are actually three changes of direction but you would count one of them as part of a different cycle, so we are back to two changes of direction in a cycle.
 

nsaspook

Joined Aug 27, 2009
6,279
Zero to a value or a value to zero is not a change in direction or sign, it's a change in value/magnitude. If you're French, 0 is positive and negative at the same time.:D
 
Albert, if you count the one between the two cycles, then you would have to also count the one at the end of the two.
 

SamR

Joined Mar 19, 2019
1,151
Give it up guys he is a troll. Doesn't matter what you say he is always correct so don't waste any time or effort here. Seems he has some undeclared method of changing time so the electrons "jiggle" the way he wants them to.
 

Thread Starter

Alchemy One

Joined Oct 5, 2019
89
My scope says that my 60 Hz house current (when there is a load) changes direction 60 times per second, my frequency counter seems to agree with that so I have to agree with the consensus.

I also read this on the Internet:
"An alternating current will flip the direction of charge flow (60 times a second in North America (60 Hz) and 50 times a second in Europe (50 Hz)). This is usually caused by a sinusoidally varying current and voltage that reverses directions, creating a periodic back and forth motion for the current".

It's pretty common knowledge that they can't put stuff on the Internet unless it is true so it must be true. I also read that on the Internet.



Maybe this would go better if you explained, in detail why you think this is false rather than have everyone else state why they feel it is true. This way people would better understand your exact, well defined, thinking on the frequency of AC current.

Ron
You and I are both on the internet right now and we are reading it. I agree if it wasn't true they wouldn't be saying.
I believe in god, then the guy asked me which one?
I answered let me check with Ron. (just off the subject dry humor)

The only difference between you and me is this: the Internet is you and me and wait also these people. and these other people here and those........ and all of the ones everywhere. ....
https://www.quora.com/How-many-times-does-AC-current-change-its-polarity-in-one-second
 
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