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Current amount in AC

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joseche

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Maybe I am not understanding clearly but this is my question:

With AC, the polarity of the voltage is constantly changing, at a 60Hz rate, it means it goes from ~120v to ~-120v, but that change is in voltage, the force that atracts or retracts electrons.

What about the current load, are electrons being moved, pushed and pulled ?, if that is the case what is the amount ?
 
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The voltage and resistance of the load determines how much current. The calculation for current is V/R which is called Ohm's Law.
120V/1000 ohms= 0.12A. 120V/100 ohms= 1.2A. 120V/10 ohms= 12A. 120V/2 ohms= 60A.

120VAC is the RMS voltage which swings from 0V to +170V then through 0V again to -170V, over and over.
 
so that means that there is no current flowing on AC, just the force to pull & push....

that makes a lot of sense audioguru!
 
Maybe I am not understanding clearly but this is my question:

With AC, the polarity of the voltage is constantly changing, at a 60Hz rate, it means it goes from ~120v to ~-120v, but that change is in voltage, the force that atracts or retracts electrons.

What about the current load, are electrons being moved, pushed and pulled ?, if that is the case what is the amount ?

This is actually a good question (one that was not answered by replies so far, by the way). If I read your question correctly, you're asking about the polarity of the current, in addition to its magnitude, right?

As you seem to suspect, yes, the current changes direction each half-cycle, going from positive to negative. So assuming the current is equal in both halves of each cycle, it goes from +X to -X at a rate of 2F. Taken over a complete cycle, the total current comes out to zero.

Is that what you were asking about?

By the way, Jackdaniel, if you think about your answer, you do realize how ridiculous it is, don't you? (Hint: the output of a microphone is AC.)
 
My little clock radio does not draw "more than 100A" of AC current. Its max AC current is only about 0.017A.
 
My little clock radio does not draw "more than 100A" of AC current. Its max AC current is only about 0.017A.

Well, in fairness to Jackdaniel, I'm pretty sure what he meant is that AC household power is capable of delivering 100 amps or more of current. Right, JD?

Of course, AC covers a lot more than the juice that comes out of your wall outlets ...
 
Actually no, the limit on most household outlets is 15A. Some utility outlets go as high as 30, like the ones on dryers and AC compressors. The limit on the master breaker in the fuse panel is usually 100A, but without connecting something directly to the master (very unsafe), you wouldn't be able to get that much current out of a household utility system. Industrial systems can have very high currents, in the kA.

The net current flow for AC is zero, but the work done is not dependent on current direction. Otherwise, anything plugged into an outlet would consume zero power. Peak currents either negative or positive in AC are only limited by the physical characteristics of the power delivery system. There is no limit to the current AC can deliver because voltage is alternating instead of direct. Though, there are system dependent limitations due to the reactive characteristics present in an AC system that are not present in a DC system. The ease in which AC power can be delivered far outweigh those disadvantages.
 
I understand that the net current on AC is zero, but that doesn't mean electrons didn't move. It means the same amount moved in one direction and the backwards.

So if at home I turn the TV on, that adds resistance and that adds current to the line, that current is moving back and forth.
If I turn the PS3 on, that adds even more resistance so now I have a little more current going back and forth at a frecuency of 60Hz.

If I go turning everything ON I am adding resistance and then current to the AC line, that current goes back and forth so the net current is zero, BUT amount of current that goes back and forth is increasing every time I turn something ON.

Is that the case ?, that will explain why the main switch will heat up if everything is on, because the current going back and forth is bigger, so much movement creates heat
 
I understand that the net current on AC is zero, but that doesn't mean electrons didn't move. It means the same amount moved in one direction and the backwards.

Yes. Keep in mind that the net current is only zero over a period of time. The instantaneous current (current at any given moment) is still in one direction only.

So if at home I turn the TV on, that adds resistance and that adds current to the line, that current is moving back and forth.
If I turn the PS3 on, that adds even more resistance so now I have a little more current going back and forth at a frecuency of 60Hz.

Yes, but you've got it backwards. When you turn on an appliance, you're actually subtracting resistance. In other words, you're reducing the total resistance within your house across the line. The less resistance, the more current.

The "electrons still go back and forth" at 60 Hz; it's just that more of them go back and forth (more current). I put that in quotes since it turns out that it's not so simple as we've been told, about how electrons flow to produce electricity. (In fact, I read something recently that explained that it actually takes years for electrons to move down a power line!) But for the sake of our discussion, it'll do just fine.

If I go turning everything ON I am adding resistance and then current to the AC line, that current goes back and forth so the net current is zero, BUT amount of current that goes back and forth is increasing every time I turn something ON.

Is that the case ?, that will explain why the main switch will heat up if everything is on, because the current going back and forth is bigger, so much movement creates heat

Yes; more electrons flowing (remember, at any given instant) produce more heat. Which would be the case even if you had DC power running through your walls instead of AC (which would mean it flows only in one direction).

Does that help any?
 
Great!,

Yes it helps a lot, so, more things connected on the circuit will mean less resistance => more current.

Thanks guys, this forum really rocks !
 
It's tempting to think that you're adding resistance when you plug something in; after all, you're putting a resistance on the line that wasn't there before.

But keep in mind that an open circuit has infinite resistance, so you're actually lowering the resistance (from infinity) when you turn on the first thing on your line. Further resistances (loads) go in parallel to any existing resistances, further reducing the total resistance (and increasing the total current).
 
You may also measure the current in AC using a digital multimeter set to current measuring mode.. "10A" Jack, although i did't do that thus do it at ur own risk!
 
Current flow is still a bit of a mystery in some respects. The electrons move slowly, but the force moves very quickly. Also, current flow is not just electrons, it can include the flow of positively charged particles in the opposite direction. For example, in a lead-acid battery, it's the positively charged particles that flow inside the battery and the negatively charged particles that flow through the wires outside the battery. The conventional direction of current flow is with respect to the positively charged particles even though electron flow is in the opposite direction. It can be hard to wrap your head around all the aspects of current flow, let alone the understanding of AC currents.
 
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You may also measure the current in AC using a digital multimeter set to current measuring mode.. "10A" Jack, although i did't do that thus do it at ur own risk!

Just a little note on this subject. When measuring current be it AC or DC current using a meter be it analog or digital meter, the meter is placed in series with the load. What this means is that it is very unwise to set a meter to the 10 amp AC current range (or any current range) and place the probe tips across a wall outlet. Really, really bad and ugly things will happen. Your meter will likely be ruined, your day will be ruined and likely after the big flash and pop your finger tips may be slightly blackened. This assumes that a molten piece of metal from a probe tip does not fly into your eye in which case you will have more problems. The trick becomes knowing how to use the meter and configure the measurement. Don't laugh as people actually shove the meter leads into a wall outlet with a curiosity about current.

Ron
 
Ron, Ron, Ron.

You had to tell them all that. Now they will do just that because they did not read (or understand) your little disclaimer about that very unwise thing.

Nobody should screw around with the mains supply unless they really know what they are doing (and by than you don't have to ask questions anymore). That goes double (actally 4x) for the Europeans (ha)! E
 
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