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I have a laptop with partially damaged internal fan. Dont want to buy new one. I am thinking of swapping the internal fan to a 12V fan. The 12V fan I have can fit as it is small. Internal fan is 5V.

Most solution out there

  • uses external power supply to power 12V fan
  • uses 5V from usb to power 12V fan
  • uses laptop charger to power 12V fan but laptop is not connected

What I want

  • power up 12V fan using laptop charge WITH laptop connected. 12V voltage level will be achieved using a step down converter with 19V laptop charger as input. OR connect in parallel to an existing 12V connection in motherboard circuitry.
  • 5V usb is good idea but I want to operate the fan at its full power using 12V.

Point of doubt

  • Laptop charger is already used to supply power to laptop. External load (fan) will definitely drain current but will it interfere with the normal laptop operation?

Question

  • can i use buck converter to step down voltage to power up 12V fan safely?
  • is laptop charger capable of giving more juice even when it is already used on laptop?

Do please share your knowledge. Much appreciated. Thanks!

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  • \$\begingroup\$ Battery is usually 11.1 so try using it directly? \$\endgroup\$ – user3528438 Apr 27 '17 at 19:06
  • \$\begingroup\$ Anything you plug in your laptop will draw extra current from the PSU, so I don't see why a fan would be a problem. \$\endgroup\$ – Dmitry Grigoryev Apr 28 '17 at 12:44
  • \$\begingroup\$ @user3528438 that would certainly be ideal but i dont use battery ><. But this made me think of using the charging port of battery to power up the fan. my battery is rated 14.4V. that means the port supplies around that voltage too. using that voltage to power up 12v fan should be ok, right? \$\endgroup\$ – iHateUni Apr 28 '17 at 18:12
  • \$\begingroup\$ @DmitryGrigoryev the concern is with the doubt that laptop charger supplies just enough juice for normal operation. i think the charger can supply more current for safety factor but im afraid using external things may cut down the safety factor \$\endgroup\$ – iHateUni Apr 28 '17 at 18:14
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Instead of using buck convertor. You can find many small boost convertor modules. Buy it and fix it within your laptop near internal fan. Supply it with original 5V supply of laptop for fan.

Regarding your Questions: I dont think there will be a problem using buck convertor with charger.

NOTE: Replace original fan with the fan which have same number of wires. Usually they have third wire for feedback to control the speed of fan and temperature of CPU

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  • \$\begingroup\$ I fail to see the benefit of converting 19V to 5V only to boost it back to 12V afterwards. \$\endgroup\$ – Dmitry Grigoryev Apr 28 '17 at 12:45
  • \$\begingroup\$ laptop fan is 5v with three wires. 12V fan I have also come with three wires. IF I replace 5V to 12V fan, can I plug in the feedback pin of 12V fan to the fan pin of motherboard in a laptop? \$\endgroup\$ – iHateUni Apr 28 '17 at 17:58
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Yes, you would use a voltage regulator. Depending on the current required by the laptop + the current required by your fan, you can tell how much the charger could support. An extra 100 mA for a fan won't affect it much.

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Depends on the power of the fan, if it is low enough. What I did: grabbed one of the step up modules from ebay, they even come with a a potentiometer to adjust the output voltage. Powering it from USB and I can even adjust the fan speed.

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