Author Options:

how to power multiple fans from a laptop? Answered

I'm currently working on a laptop to somewhat of a desktop conversion.  The laptop has really bad cooling so i have drilled into the case and added some big fans.  Its probably overkill yes, but if it works then who cares.  

I've added two fans.  One is a 24V DC .20A fan and the other is a regular DC motor.  I'm wanting to power them from the laptop.  I'm not sure how to do that though.  I've tested them both separately on a USB and they are very slow and almost useless.  Is there a way to combine two USB ports for more juice?  Any ideas or suggestions?  Thanks.


Nope!. Not going to work. I suggest you either use a separate power source or buy USB fans.

You can't increase voltage when the source is the same. If you had 2 different 5V sources wired in series you can get 10V. But since the USB is all working off the same source you won't get increased voltage.

DO NOT CONNECT THOSE FAN TO THE USB PORT AGAIN. You will likely burn out the 5V rail of the laptop as they will try to pull more amperage than the ports can provide.

Ok, thanks. So i found an old DC wall outlet with an output of 9 volts. I'll just wire up the fans in parallel and use that.

9V isn't going to do much for a 24V fan. How many watts does the fan pull? How many amps can't the wall adapter support? What it can't get in voltage it will get by drawing more amps. This burn out the wall wart over time or cause it to catch fire.

I don't know anything about the motor connected to the laptop shell. All i know is that it's a regular DC motor. Here's some pictures:

photo 1.JPGphoto 2.JPGphoto 3.JPG

The 24V fan wants .2A which is 200mA. Stick with the 21V wall wart and you'll be fine. Those things tend to put out a bit more voltage then the label shows.

The other fan is a nice fan and will work better if you put a duct over ti to channel the air across the circuit board. No telling the rating of the motor unless it's marked somewhere. Try the 9V adapter on it and see how it goes.

The 9V works will the unlabeled fan. But, the fan connected to the 21V is spinning WAY too fast for my purposes and liking. How do i slow it down? Shouldn't i just use a lower voltage?