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12v DC fan with 12v wall power adapter, versus 120v AC fan plugged directly into wall. Which is better?

What is better?

A 12v DC fan with a power supply
Fan like this, and power supply like this.


A 120v AC fan plugged directly into wall
Fan like this.

The 120v AC fan has a larger motor while the DC fan has a smaller motor.
What kind of motor does the 120v AC fan use? Is it a shaded pole motor?

NOTE: The fans in the pictures are just examples; I am not talking about those exact fans. I'm talking about any fan.
14 answers Last reply Best Answer
More about 12v fan 12v wall power adapter versus 120v fan plugged directly wall
  1. Best answer
    The Delta DC fan is rated at 4000RPM, 148 ft^3/m, and 15.3 mm H20 static pressure. 51dB (A) noise.

    The CoolTron AC fan is rated at 2500RPM, 105 ft^3/m, and 7.6 mm H20 static pressure. 43dB (A) noise.

    The DC one will be much more effective, though louder.
  2. The DC fan on the other hand will add more heat into the air it is blowing. AC runs cooler than DC, that's why power lines are AC (ala Tesla) instead of DC (which is what Edison wanted)

    Of course it probably is NOT much in this case :)
  3. NO, that is not it.

    While this particular DC fan is more powerful than the AC fan, and will thus put more heat into the air, it is absolutely not due to the AC/DC difference.

    AC can be more easily stepped between voltages, allowing utility companies to use high, unsafe voltages for efficient transmission of large amounts of power, while using safer, lower, less efficient voltages for the shorter distances from distribution nodes to homes.
  4. I'm not talking about these exact fans in the pictures, I'm talking about in general.
  5. DC power can't be carried over the same long distances as AC, watt per watt, because DC would melt the cables.
  6. No. For very long transmissions, DC is actually used instead of AC because you don't have phase issues. You just have to use high voltages, like long distance high power AC transmission.

    https://en.wikipedia.org/wiki/High-voltage_direct_current
  7. Anonymous said:
    I'm not talking about these exact fans in the pictures, I'm talking about in general.


    This varies widely between fans. In general, an AC powered fan is going to be more powerful. But there are plenty of extremely powerful DC fans too.
  8. Someone Somewhere said:
    Anonymous said:
    I'm not talking about these exact fans in the pictures, I'm talking about in general.


    This varies widely between fans. In general, an AC powered fan is going to be more powerful. But there are plenty of extremely powerful DC fans too.


    But for a DC fan you'd need to convert 12v AC to 12v DC, then the fan does it's thing. With an AC fan you can just plug it directly into wall. So would the AC fan be more efficient?

    If so then the AC fan is better, right?
  9. backoffmanImascientist said:
    DC power can't be carried over the same long distances as AC, watt per watt, because DC would melt the cables.


    Oh no I accidentally marked your reply as a solution. :ouch: Can some mod please undo it?
  10. Deselected.

    120VAC to 12VDC. The AC>DC power supply won't be particularly efficient, but that's going to be no more than a couple of watts. And it's usually run off the same power supply as most of the equipment it's cooling, which uses an order of magnitude more power.

    When used inside a PC or server (where most fans like these are used), running it off DC means that you don't have to worry about mains wiring. Which is a significant safety improvement.
  11. Someone Somewhere said:
    Deselected.

    120VAC to 12VDC. The AC>DC power supply won't be particularly efficient, but that's going to be no more than a couple of watts. And it's usually run off the same power supply as most of the equipment it's cooling, which uses an order of magnitude more power.

    When used inside a PC or server (where most fans like these are used), running it off DC means that you don't have to worry about mains wiring. Which is a significant safety improvement.



    So lets say I have something like a cabinet or bin for storage, and I need a/some 80mm or 120mm fan(s) to ventilate it. And you did not already have fans or power supplies, requiring you to buy new ones. Would you get the AC fan(s) or would you get the DC fan(s) with a power supply?

    A DC fan would probably be cheaper, and often someone would already have the parts needed. And with a DC fan, you can change the speeds of them with resistors or diodes or voltage regulators. With an AC fan you can't. But an AC fan may be more efficient.
    Also... Why does an AC fan have a bigger motor? What kind of motor is it? Shaded pole motor?
  12. I don't know what sort of motors they're using in AC fans. I'm also not certain why they're larger.

    An AC fan would probably be cheaper if you include the cost of a power brick. Maybe DC would be cheaper if you had several.

    The main reason for running fans at <100% is noise. Typically, AC fans aren't going to be used in the midst of a large number of people.
  13. Someone Somewhere said:
    I don't know what sort of motors they're using in AC fans. I'm also not certain why they're larger.

    An AC fan would probably be cheaper if you include the cost of a power brick. Maybe DC would be cheaper if you had several.

    The main reason for running fans at <100% is noise. Typically, AC fans aren't going to be used in the midst of a large number of people.


    "An AC fan would probably be cheaper if you include the cost of a power brick."

    Do you mean DC fan? You wouldn't need a power brick for an AC fan.

    So I think DC fans would be better because they are cheaper and more common, and many people would already have the parts (like a 12v power supply). And you can change the voltage. And they are probably safer too. Plus the AC fans are more expensive and heavier because they have more copper and other metal materials.

    So I have come up with my own answer: DC fan with power adapter.


    Also, I believe the AC fans use a shaded pole motor. In this video, he shows a shaded pole motor with a propellor that looks like it came from an AC fan like we are talking about. Also, I've seen a few videos of an AC axial fan like this starting up and they sound just like a table fan with a shaded pole motor starting up.
  14. No - the AC fan doesn't need the cost of the power brick, so it's cheaper than the DC fan including the power brick.

    The question is whether a good power supply (would you trust something cheap running 24/7 in a hot environment with no-one watching not to catch fire?) is more than the difference? I doubt it is.

    Why would you need to vary the speed? And if you're worried about efficiency, putting a resistor in series is about the worst thing you can do.
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