Complete beginner trying to manipulate current and voltage

Discussion in 'Power Electronics' started by Jeppe Hagh Møller, Mar 4, 2018.

  1. Jeppe Hagh Møller

    Thread Starter New Member

    Mar 4, 2018
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    I am new to building circuits, so I am pretty lost...

    I am building a laptop cooler, but I think the fan is too large to be powered by a USB output. I tried, and the fan moves an inch or so, but then it stops again. It is rated for 12V and 80mA. It is this one: https://noctua.at/en/nf-a20-flx

    I then want to power it from the mains instead, and I have a converter from an old hair trimmer that outputs 6V and 650mA.

    Can I use that? If so, how would I build the circuit? Should i go about this project in a totally different way?

    Would it be possible to control the fan speed with a potentiometer?

    Hope someone can help me.
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Welcome to AAC!
    The fan is rated for 12V. USB is only 5V and the adapter is only 6V. Why do you think either would be enough?
    The function of the 3 pins in the connector is unclear from the specification.
    What does the "LNA" referred to look like?
     
  3. crutschow

    Expert

    Mar 14, 2008
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    No, look at its spec.
    It is a 12V fan and you are trying to power it from the 5V USB power.
    You need a 12Vdc source to power that fan, such as a 12V ≥0.2A wallwort supply.
    Or buy a 5V fan.
     
  4. dl324

    AAC Fanatic!

    Mar 30, 2015
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    There's a reason why the rating is specified...
     
  5. Jeppe Hagh Møller

    Thread Starter New Member

    Mar 4, 2018
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    Thanks for the replies!

    I guess i was just thinking that I could amplify the voltage using an op-amp or something. Is that not possible?

    I have acces to all kinds of components, and thought it would be fun as a hobby project.

    The fan is not cheap, so I guess I will have to find another adapter if it can't be done
     
    Last edited: Mar 4, 2018
  6. dl324

    AAC Fanatic!

    Mar 30, 2015
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    Not practical with an opamp. The output current for most is on the order of 25mA and an opamp's output voltage can't exceed it's supply voltage...

    You could use a switching (boost) regulator to step up 5V to 12V.
     
  7. Jeppe Hagh Møller

    Thread Starter New Member

    Mar 4, 2018
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    Okay thanks, I will look into that.

    In case i find a 12V adapter, chances are it won't be exactly 80mA. Will a higher current damage the fan?
     
  8. dl324

    AAC Fanatic!

    Mar 30, 2015
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    No. You were already advised to get something higher than 80mA.
     
  9. crutschow

    Expert

    Mar 14, 2008
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    Most devices take only the current they need, independent of how much current the source can supply.
    Thus you can connect the fan to a 12V car battery which can deliver several hundred amps, and it will still take only the 80mA it needs.
     
  10. WBahn

    Moderator

    Mar 31, 2012
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    Think of all the things you have that are powered by a 9 V battery. They don't all require exactly the same current, do they? So why doesn't this battery that can power a circuit requiring a few hundred milliamps not damage a circuit that needs less than one milliamp? It's because the battery is a voltage source (though not a very ideal one) and will supply whatever current is needed (within its capabilities) to maintain 9 V across it's terminals. If it only needs to supply a microamp, it will only supply a microamp. If it needs to supply 100 mA, it will supply 100 mA. At some point it can't supply the necessary current and the voltage starts to drop.
     
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