- #1
Aditya Mysore
- 6
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how do the appliances work with AC voltage when the polarity keeps changing?
How do the appliances work with AC voltage?
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Discussion Overview
The discussion revolves around how appliances operate with alternating current (AC) voltage, particularly focusing on the implications of changing polarity and current direction. Participants explore various types of loads, including resistive loads and motors, and the conversion of AC to direct current (DC) for sensitive electronic devices.
Discussion Character
- Exploratory
- Technical explanation
- Conceptual clarification
- Debate/contested
Main Points Raised
- Some participants explain that for resistive loads, power remains positive throughout the AC cycle despite the changing polarity, as both voltage and current are positive in one half and negative in the other.
- Others argue that AC appliances are generally not polarity conscious, meaning they do not require a specific positive or negative supply as batteries do.
- A participant notes that light bulbs do not respond to changing voltage and polarity due to their slow response time, while sensitive systems typically convert AC to DC.
- It is mentioned that most electronic devices, such as TVs and computers, do not operate directly on AC but instead convert it to various DC voltages.
- One participant emphasizes that the definition of AC is that the current alternates direction, raising questions about how appliances manage this characteristic.
- Another participant explains that the ability to transform voltages efficiently is a significant advantage of AC, allowing for the use of transformers without power loss.
- Further, it is discussed that power supplies for devices convert AC to DC and then back to high-frequency AC for efficient voltage transformation.
Areas of Agreement / Disagreement
Participants express a mix of agreement and differing views on how appliances handle AC voltage. While some points about the nature of AC and the operation of resistive loads are acknowledged, the discussion remains unresolved regarding the specifics of appliance operation and the necessity of AC to DC conversion for various devices.
Contextual Notes
There are limitations in the discussion regarding the assumptions made about the types of loads and the specifics of how different appliances manage AC voltage. The conversation does not fully address the technical details of the conversion processes or the implications for various appliance types.
- #2
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Think of a resistance load. For the first half of an AC cycle voltage is plus and current is plus. Power is voltage times current, thus plus. In the second half of the cycle voltage is minus and current is minus, but voltage times current is still plus. (-1 * -1 = +1). So the directin of power flow is the same through the whole cycle.
- #3
- #4
davenn
Science Advisor
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Aditya Mysore said:
primarily, because in general, AC appliances are not polarity conscious ... that is, they don't need a specific + and - supply like from a batteryDave
- #5
meBigGuy
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A light bulb does not care that the voltage is changing and polarity is reversing because it has a slow response time.
For systems that are sensitive, the AC is converted to DC. In fact, that is true for most appliances (other than toasters, heaters, AC motors, etc).
There is nothing in your TV that runs off the AC directly. It is converted to many different DC voltages. Same for your Computer.
For systems that are sensitive, the AC is converted to DC. In fact, that is true for most appliances (other than toasters, heaters, AC motors, etc).
There is nothing in your TV that runs off the AC directly. It is converted to many different DC voltages. Same for your Computer.
- #6
Aditya Mysore
- 6
- 0
Then you mean to say the current keeps changing its direction?anorlunda said:
- #7
davenn
Science Advisor
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Aditya Mysore said:
yes. that's its definition ... AC = Alternating Current
Dave
- #8
Aditya Mysore
- 6
- 0
Well
That was my initial question.
Well then how can an appliance handle such kind of a thing when the current in the circuit keeps changing its direction?davenn said:yes. that's its definition ... AC = Alternating Current
Dave
That was my initial question.
- #9
meBigGuy
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Did you read my reply? #5
- #10
Aditya Mysore
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Yes I think you are right. Thanks :)meBigGuy said:
- #11
meBigGuy
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Aditya Mysore said:
It doesn't matter that I am right
, does it fully explain what you wanted to understand?In order to efficiently transform voltages you need AC power. The changing currents allow one to use transformers to efficiently change voltage without power loss. For example, 110VAC 0.1 Amp (11 watts) applied to a proper transformer would power a circuit that requires 5VAC 2.2A (also 11Watts). That ease of voltage transformation is one thing that make AC very useful. Then, after transforming voltage, there are very simple techniques to convert the AC to DC, which most electronic circuits require.
Your PC power supply (and most wall-wart chargers) do this to an extreme. They convert 110VAC/60Hz directly to DC and then chop it back into AC at high frequencies (100KHz or higher) to put it through a transformer that creates many AC output voltages. Then they convert those back to DC, say 5V, 12V, and 3.3V to power a PC. For various other reasons, creating 100KHz AC allows efficient power transfer through a cheaper, smaller transformer.
So, AC is not a problem for appliances, it actually makes it easy to transform the power to voltages needed by an electronic system. Most don't actually run on AC internally.