Why is the correct polarity important with AC?

In summary, the correct polarity of AC matters because it affects the direction of current flow, which can be important in certain circuits. This is why it is important to connect live to live and neutral to neutral in wall outlets, even though AC itself has no polarity. In some cases, such as with non-polarized plugs in Europe, the polarity may not matter as much due to different wiring conventions. As for AC to DC converter circuits, it is often a convention to mark one side as hot and the other as neutral, but this may not always be necessary. It is also worth noting that this forum may allow the posting of YouTube videos as links rather than as videos themselves.
  • #71
artis said:
Sure but they only look like that on drawings because in real life when one uses the 240v outlet the center tap is not used by that device/outlet
I’m not sure how that relates to my answer, so I guess I’ll try again.

1. Scope between outer taps - one 240v rms sine. Centre not involved.

2. Using a two-channel scope, connect one probe common to centre, and its tip to one outer tap. Connect the other probe tip to the other outer tap. Displaying both channels simultaneously, you will see two sines, 120V rms 180deg apart.

^^^ This is a thought experiment. There are safety issues to consider when probing mains voltages.
 
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  • #72
@Guineafowl thanks, I already understood that by the fact that @Averagesupernova said about the measurement being relative to center tap but you beat me to it
 
  • #73
Guineafowl said:
It’s an IT system in Norway, I believe. Isole-Terre.

It’s pointless attempting an Earth return path through the rocky terrain, so the supply transformer is not earthed at all, or only through high impedance. The installation has a local earth.
Spot on!
 
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  • #74
Hello just stumbled upon this.. trying to understand how diode bridge works. Is it an assortment of 4 different diodes , are they configured a specific way ? I am a bit confused on the construction. Any help would be great. Also why would this be necessary in a situation like this ?
 
  • #75
chipresistor122 said:
Hello just stumbled upon this.. trying to understand how diode bridge works. Is it an assortment of 4 different diodes , are they configured a specific way ? I am a bit confused on the construction. Any help would be great. Also why would this be necessary in a situation like this ?
This wikipedia article is pretty good : https://en.wikipedia.org/wiki/Diode_bridge

1606880037433.png


There is a non-planar crossover (the little half circle) in this bridge circuit ##-## that crosser can be replaced with 3 XOR gates to make it planar, arranged as shown here:

1606879120468.png

. . . and each those can be relaced by 4 NAND gates arranged as follows:

1606878936344.png


That can matter in micro-circuits, but generally doesn't matter on a breadboard circuit.
 

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  • #76
sysprog said:
This wikipedia article is pretty good : https://en.wikipedia.org/wiki/Diode_bridge

View attachment 273546

There is a non-planar crossover (the little half circle) in this bridge circuit ##-## that crosser can be replaced with 4 XOR gates to make it planar, arranged as shown here:

View attachment 273544
. . . and each those can be relaced by 4 NAND gates arranged as follows:

View attachment 273543

That can matter in micro-circuits, but generally doesn't matter on a breadboard circuit.
"... that crosser can be replaced with 4 XOR gates to make it planar, arranged as shown here:"
There are only three XOR gates shown.

I don't see why a diode bridge was suggested in the context of the OP, anyway. It certainly wouldn't work for an appliance requiring an AC supply, and neither would using logic gates as part of a diode bridge in a power circuit.
 
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  • #77
darth boozer said:
"... that crosser can be replaced with 4 XOR gates to make it planar, arranged as shown here:"
There are only three XOR gates shown.

I don't see why a diode bridge was suggested in the context of the OP, anyway. It certainly wouldn't work for an appliance requiring an AC supply, and neither would using logic gates as part of a diode bridge in a power circuit.
You right ##-## it's 3 XORs, 4 NANDs each to replace them, and 4 diodes in the bridge ##-## thanks for the correction ##-## I'll edit the post ##-## as for appliances that use bridge rectifiers to convert AC to full-wave-rectified DC, there are many such devices.

Regarding using logic gates as part of the bridge circuit, they could be used in the DC part of the circuit to allow a planar crossover, like this:

1606893624932.png

The 3 XOR gates could go where the left-tilted X with the adjacent - + and + - labels is in the circuit illustration.
 

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  • #78
Sysprog , thank you for the thoughtful response. It is much appreciated I needed a refresher on how Bridge Rectifiers work.
 
  • #79
Yup that is a good explanation. Overall a bridge rectifier is just an assortment of 4 or more diodes. It comes in a pre-assembled module. They convert AC current to DC current and are generally used in power supplies or battery chargers. The assortment of diodes are used to allow current to flow in one direction only and not flow backwards. It is a really common component in our daily lives. I found another article for you to reference that should help refresh you. Talks about how it works, different applications and also has a video to go along with it Bridge Rectifier Explanation . Hope that helps ... let me know if you have any other questions. I am happy to help.

best,
 
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