I need some help with AC polarity

[USER 12]

I have been trying to understand how AC power can change in polarity or cycle and show up on a multimeter as +12 or -12. what determines the polarity at the time you check the voltage? Does this have something to do with the direction or the source? How?

 

[bobdole369]

There is no such thing. Typically AC has a "hot" and a "neutral" wire. If you touch the black to hot, and the red to neutral, on a meter it will show the negative sign. Its not because there is a polarity, its there to help electricians figure out how to not burn down the house LOL.

 

[Witling]

If you're readomg +- 12 volts in a computer or a car, you're reading DC.

 

[Bassyhead]

60Hz AC consists of a sinusodal wave that completes a cycle 60 times per second. Since the "polarity" is constantly changing, you're not going to be able to measure it with a DC meter. You need a meter that will measure AC.

 

[bobsmith1492]

There is such thing as AC polarity; however, it won't show up on a meter as +/- voltage, since that changes 60 times / second. AC polarity has to do with the phase of the signal - what point is the signal at at a particular point in time. I guess it only really matters if you're trying to parallel two AC lines from two transformers or two separate windings.

 

[USER 12]

Thanks of all the help, all the replies helped me out, now I know why I was having trouble with it, I did not understand I was dealing with DC inside the PC.

 

[Mday]

Originally posted by: USER 12
Thanks of all the help, all the replies helped me out, now I know why I was having trouble with it, I did not understand I was dealing with DC inside the PC.

digital systems use DC. any AC involved would be a signal or data.

 

[The Boston Dangler]

Almost any device will use DC internally. AC is almost always used for power and signal transmission.

Notable exceptions: AC motors, light bulbs, toasters. Not much else.

 

[PowerEngineer]

Everything stated so far is right on the mark.

The advantages of AC (over DC) are that it allows for simple (brushless) motors and can be stepped in volytage for more effecient transmission (and stepped back down again for end-users).

The AC voltatges and currents are cycling sinusiodally sixty times a second, which is too fast for a DC multimeter to track. The AC scales effectively rectify voltage to show the RMS value of the AC voltage.

Most all elctronic devices use DC voltages which are produced by a power supply that steps down and rectifies the AC input voltage to DC.

 

[piddlefoot]

ac= +-+-+-+-+-+-+-+- osilation we use around 50 =60 hertz, pos neg current on same line defeats downfall at a better percentage than dc power

dc=direct current , no osilation.

our power system is worldwide ac power , something a man called Nicola Tesla gave us ac power, yet we all know who Edison is.......meh.....but thats a different story.....

u can have low voltage ac currents or high but usually for practical uses its needed to be converted back into dc for most appliences.

A tesla coil is fed ac power , but then thats why he created ac power, because nothing else could power it up as good or Efficiently.
l have pics of my toy tesla coil , thats fryed a mobile phone and watch l forgot l had on me , its located in my 2 bay shed obviosly on its own its only 20cm high, but far out can it output some voltage, l;l can get little pretty blue sparks between dozens of EMPTY beer cans, looks wikid , get a coil for electrical experimentation, BUT BE CAREFULL, they can KILL YOU , but you just learn and understand electricities properties better.......

enjoy.........

 

[Woodchuck2000]

Originally posted by: piddlefoot
ac= +-+-+-+-+-+-+-+- osilation we use around 50 =60 hertz, pos neg current on same line defeats downfall at a better percentage than dc power

dc=direct current , no osilation.

our power system is worldwide ac power , something a man called Nicola Tesla gave us ac power, yet we all know who Edison is.......meh.....but thats a different story.....

u can have low voltage ac currents or high but usually for practical uses its needed to be converted back into dc for most appliences.

A tesla coil is fed ac power , but then thats why he created ac power, because nothing else could power it up as good or Efficiently.
l have pics of my toy tesla coil , thats fryed a mobile phone and watch l forgot l had on me , its located in my 2 bay shed obviosly on its own its only 20cm high, but far out can it output some voltage, l;l can get little pretty blue sparks between dozens of EMPTY beer cans, looks wikid , get a coil for electrical experimentation, BUT BE CAREFULL, they can KILL YOU , but you just learn and understand electricities properties better.......

enjoy.........

Oh great, you again... I think you'll find that William Stanley Jr developed the first AC device almost ten years before Nikolai Tesla was on the EE scene. Edison was almost entirely obsessed with DC and was a little miffed when Tesla showed that AC transmission of power is more efficient. Oh, and AC Current is tautological (Look it up).

 

[piddlefoot]

stiff whoopy who gave us the ac system we use today ? wasnt Edison ,William Stanley Jr, but Tesla whom made it into a usable system , and how much do they teach at public school on Tesla ? They teach Edison mostly, Testla hardly ever gets a mention, on top of that get yourself a Tesla coil, and wind it up tune it in and suss out there potential, its just awsome , to think its over 100 years old.....