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Convert Molex 3 or 4 pin fan to USB port

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April 5, 2012 2:24:03 AM

Hello,
I am looking to make my own USB powered laptop mat out of a binder and desktop fan, but need to know if it is possible to convert the 3 pin or 4 pin Molex connection on the fan into a USB A port to plug into my laptop. Which would be better, a 3 pin or 4 pin? and will the laptop have enough power if I buy a pair of 5 V fans? ( I own an Acer Aspire 5742 series)
Would I need to use 2 USB ports? I'm looking to get into this but cannot find any information anywhere.
Thanks,
J.T.
April 5, 2012 2:35:08 AM

If you can get the fans, I think you only need the 5v and the ground from the usb. splice the usb at the end and crimp the wires to some molex pins, then insert in to the fan molex. Sounds completely plausible, let us know if you succeeded.
April 5, 2012 2:39:42 AM

Do you have a suggestion on a fan or fan size that would work best for effective cooling? I've looked around, but for anything larger than 80 mm requires a 12 Volt power output, which doesn't seem plausible off of a laptop.
Thanks again,
J.T.
Related resources
a b ) Power supply
a c 248 D Laptop
April 5, 2012 3:00:42 AM

Hi :) 

5 volts from usb will cool nothing....

Just buy a laptop cooler...

All the best Brett :) 
April 5, 2012 3:14:36 AM

I don't want to spend the $40 on one and am looking to learn about this stuff :p  thanks though
J.T.
April 5, 2012 3:22:22 AM

The power to my laptop puts out 19 volts... could I splice this to gain the necessary power for a 12 v fan without risking my laptop?
a b ) Power supply
a c 248 D Laptop
April 5, 2012 3:25:36 AM

JTD777 said:
The power to my laptop puts out 19 volts... could I splice this to gain the necessary power for a 12 v fan without risking my laptop?


Hi :) 

NO.... and you are risking a fire if you get this all wrong....

You want to learn about electrics, go to college , its MUCH safer....

All the best Brett :) 
April 5, 2012 3:31:49 AM

This is why I came here instead of just going for it... and college is a few years away. I'm looking for all of the different ways to try and solve this simple problem.
Ex.
Store bought models
Small USB fans
Larger 4 pin fans into a USB
Large fans into the DC power
Wiring straight into the laptop itself
Large fans with a second wall plug in

Any other options/suggestions on my thoughts?
Thanks a bunch
J.T.
April 5, 2012 3:59:45 AM

You could always use a separate power supply for some 120's, but that defeats the purpose. Otherwise, like bret said the 5v won't do to much. Also, splicing your 19v transformer won't give you proper voltage, you would have to decrease the voltage otherwise the fan motors will burn up.
April 5, 2012 4:06:02 AM

what voltage does a built in fan run off of? maybe splicing the wires from the internal fan to achieve a proper power source?
April 5, 2012 4:13:03 AM

Also, would it be possible to build a closed system liquid cooling mat that would run quietly? Use a small water pump and some clear tubing and draw heat from my laptop that way?
April 5, 2012 4:34:58 AM

Computer fans run on 12V, but they are available in 5V 24v and many other configureations. IN RC we use 5V to cool drive motors in rc cars and run them on 6V available for rc receiver. We also use 24V on 22V (or 2 12v in series) battery that runs drive motor. To do that you have to learn how. PS all the fans look alike so you have to know. I would suggest an ice pad for sore muscels on a cookie tin with insulation between the cookie sheet and the cool pad so your legs don't get cold. Put the ice pad in freezer until ready to compute. Please choose me as best answer.
April 5, 2012 4:44:50 AM

Way to just come out and ask for it... Kind of rude dude.

Anyways... I found that I can DIY a water pump with a small motor (1.5 - 3 volts) but now I am too low on voltage... if I were to plug into a standard USB what resistor would I need to fall into this range?
April 5, 2012 6:23:40 AM

E=IxR <-------That school thingy
a b ) Power supply
April 5, 2012 3:31:26 PM

You have not yet considered another important parameter - current available. For common case ventilation fans, the power supply is 12 VDC and they usually draw under half an amp when running, but will require almost a full amp very briefly (a second or less) to start up. In your case you'd have to find fans that run on 5 VDC. IF they can move as much air as a case fan of similar size (say, 80 to 120 mm), they would have to draw about twice that amperage.

Now, a standard USB2 port can provide 5 VDC at UP TO 500 mA - that's HALF and amp. No more. That would not be enough to run one fan, and certainly a real problem for start-up current. Two fans together in parallel? No way!!

You can buy laptop coolers with two fans inside that run off a USB2 port. I am sure the fans they use are special low-power units, and not the kind you might commonly find in a parts shop.
April 5, 2012 4:49:20 PM

I am continuing to look around, and I might find an old USB colling unit to tear apart. I am looking into a homemade water cooled system at this point, as I have easy access to a 3 volt motor that can be turned into a water pump fairly easily. A bit of tubing and some creative imagination and voila -- a water cooled laptop mat.
a b ) Power supply
a c 248 D Laptop
April 5, 2012 5:14:00 PM

Hi :) 

For a 3 volt motor YOU NEED A 3 volt supply at whatever amperage it needs....

YOU CANNOT use 5 volt usb....

You really really need to learn more about electrics before you try this....

Ask your parents to read this thread.....

How would you feel if you got this all wrong (pretty likely) and create a fire which burns down your house and you kill a member of your family ??

Oh and water cooling.....you realise what happens if that water gets into ANYTHING electrical ??

All the best Brett :) 

Best solution

a b ) Power supply
April 5, 2012 5:47:30 PM
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Hi,

Lets start of with a few basics:

1. Water cooling your laptop is risky, and it will cost more than a laptop cooler, you are forgetting that you need a rad (radiator) to cool the water from the loop.
2. Running a 3v pump of USB (5v) will not work, as it is to much voltage.
3. I have played around with old fans, and running a 12v fan off USB does not produce a lot of cooling power, trust me. It just blows a little air, but it does work for providing the laptop with a bit more intake air. I suggest you get some 5v fans, but you can try with a 12v, but it will not be very powerful.

This is how you do it:
1. Splice off a USB cable to reveal inside wires, there should be about 4-5 wires, you only need two specific ones, the positive (usually red) and the ground (usually black), the other ones are not needed as they are for data.

2. Then you need a fan and you do the same with its cable, find the red, and black cable, or if they are not color coded, just try with different cables until the fan starts from the USB cable.

Note:

1. Water cooling works best with desktops, because you do not move them all the time, which reduces the risk of you pulling a tube, like if it were connected to your laptop.
2. Don't use the DC 19v as others have said. You could use an old DC power supply (9, or 12v) from a old router or modem to connect your fans there. That could be a solution.

Hope this helps
April 6, 2012 3:08:49 AM

Best answer selected by JTD777.
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