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 Post subject: DIY project, need some advice
PostPosted: Sun Jun 17, 2007 3:50 pm 
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i guess a lot of advice will come from people with full towers and such, as i need advice for fans.

my idea is to make a laptop cooler out of some plexiglas i have lying around.

the complicated part is that i want it to be USB powered, as well as have a USB hub on it [partly because my laptop only has one USB port, and it'll suck if the only one is cooling it, and it would really bite if i need an external power supply for it, as its a laptop, that wouldn't help in the car or anything.

basically, i'd wire the fans in series, so they aren't splitting the power, its just one big loop. the problem with that is USB only supplies 5V. fans normally need 12v.

the things i need to know most are:
1) is there a way i can increase the voltage through a circuit board, if so, how.
2) what fans run best undervolted, i generally want to stick to 80mm fans, smaller is fine too, there will be either 2 or 4, depending on how large i can make the pad it will sit on.
3) has anyone else done this, if so could they offer some insight

it wont be quite the 30-60-90 degree setup, but probably an obtuse triangle shape [from the side], where the laptops platform would be the hypotenuse. [i hope that wasn't too confusing.]

also, if people make a parts list and explain it, naming the stores that i can buy the parts [as well as general price] would be really helpful.

i think i'll be using lighted fans on the plexiglass and placing them in the middle spaced apart to achieve maximum cooling. the laptop in question is a Thinkpad 2648 T22. the laptop will be resting on top of rubber grips so that it doesn't slide around, and it provides room for the air to escape.

making the general cooler is pretty much set, as i have a blowtorch, plexiglass, and i can get some fans, its just how to wire it that is a problem to me.

can anyone list the best fans that are easily undervolted to 5v, or how to increase the 5v to 12v?

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 Post subject: Re: DIY project, need some advice
PostPosted: Mon Jun 18, 2007 10:27 am 
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Joined: Wed Apr 05, 2006 9:54 pm
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Location: USA
bonestonne wrote:

1) is there a way i can increase the voltage through a circuit board, if so, how.



Yes, there are devices called charge pumps or switched mode regulators. White LED drivers often use these devices, due to the higher forward voltage of white LEDs. You'd have to look at some data sheets, but not too long ago I was looking at some LED drivers from Supertex, Fairchild Semiconductor, Allegro, Infineon, and National Semiconductor. Linear regulators like the 7812 will not work off a 5V supply. Some more general information can be found at the wikipedia page on DC to DC converters. I think it is relatively easy to build voltage doublers using switched capacitors, but I'm not sure how much current they can support.

Also, I'm not sure if I would really bother with trying to get 12V, as you probably don't want to run your fans that fast (read: loud) anyway. Sticking with fans you know will start at 5V might be good enough, especially if you have multiple fans.

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 Post subject:
PostPosted: Mon Jun 18, 2007 11:41 am 
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According to wikipedia and other sources I found: "The USB specification provides a 5 V (volts) supply on a single wire from which connected USB devices may draw power. The specification provides for no more than 5.25 V and no less than 4.35 V between the +ve and -ve bus power lines. Initially, a device is only allowed to draw 100 mA. It may request more current from the upstream device in units of 100 mA up to a maximum of 500 mA."

So you can only draw 100mA and only AFTER you request you can get 500mA. So there isn't much power to work with for many fan's, an antec tri-cool 80mm fan will use all the power in the usb port.

Reading this I think there will be more to it than just soldering some wires together, but you also have to request power from the usb one way or the other.


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 Post subject:
PostPosted: Mon Jun 18, 2007 4:01 pm 
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I was thinking about the USB current limit as well, but aren't most laptop coolers USB powered? I suppose you could look up the symbols used to request the extra current, and hardwire it to always send them when the device is plugged in, depending on how long and how many symbols are used. But as I said, with so many laptop coolers that are USB powered, you may not have to do anything special. It would be nice if you could find pictures of a disassembled unit, like in a review.

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 Post subject:
PostPosted: Sat Jun 23, 2007 11:14 am 
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Location: Northern New Jersey
i know someone with a USB laptop cooler, which is where the idea of this being USB powered came from.

after i get my hands on a 4 port USB hub, i'll see how the hub splits the USB cable into 4 ports, and take it from there..it'll be interesting..i've googled the pinouts and all, but its only 5v...even undervolted fans normally rely on a 12v draw at the beginning to start them. we'll see. i haven't dropped the idea...just kept trying to find a way to go from 5v to either 12v or 7v

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