I just made a little desktop fan from two casefans and other lil bits i had laying around, ATM i am running it from a molex connection but would like to run it through a USB port for portability reasons.

USB power has 5v, correct? how would i get 12v out of the USB port?

heres a pic of it

sorry about shabby quality, had 2 take the quality down on adobe.

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You can get 12vDC from 5vDC (either electronic with a board with an ICL7600 or similar, or solid state with a bass-ackwards transformer - I wouldn't have an igloo about the former, but I could bodge the latter ), but franky I'd be worried about just how much of load 2 fans are going to put on the USB headers, & the ikkle tracks that power them .... more than enough to go fzzzt! I'd guess

I think your best bet would be a cheap mains powered 12v adaptor - a fiver or so from Argos

Just mod a functioning molex plug into the back of your case.

I don't think you can get 12v out of a USB port.

i guess that would work, but i would like to keep the amount of plugs i have 2 a minimum, i'm already having to take plugs out and swap them around whenever i want to scan.

i'm already running off a molex out the back of my case....so i guess i'm gonna have to stick to the molex then

If you desire a USB plug that badly you could dedicate one port on a PCI USB backplate for 12V power by wiring the pins meant for the motherboard to a a molex plug internally.

Better put a warning sticker on the port though, it'd trash any USB device you plug in to it.
Red is +5v, White is Data -, Green is Data +, and Black(s) is Ground.
I'd combine two wires for +12v and two for Ground, to ensure enough power for to the fans.

Splice a spare USB cable and wire it to the fan's using the same colors for positive and negative as you did internally.

Quote: Originally Posted by TekXoID If you desire a USB plug that badly you could dedicate one port on a PCI USB backplate for 12V power by wiring the pins meant for the motherboard to a a molex plug internally. Better put a warning sticker on the port though, it'd trash any USB device you plug in to it. Red is +5v, White is Data -, Green is Data +, and Black(s) is Ground. I'd combine two wires for +12v and two for Ground, to ensure enough power for to the fans. Splice a spare USB cable and wire it to the fan's using the same colors for positive and negative as you did internally.

that would be a good idea, but the only reason i really wanted USB was so i could take it from PC to PC and maybe even show it off in my IT class.... i'm doing something similar though, just getting rid of the USB and throwing in 2 molexs on a PCI plate... already have a plate and the wires ready, all i need to do now is cut the hole in the plate, i'll probably do it in school on tuesday.

Quote: Originally Posted by Jonny English or solid state with a bass-ackwards transformer

IIRC, transformers only work with AC voltages. There might be a way to do it electronically, but i'll be buggered if I know how.

Your fans might put out enough air on 5 volts, then again they might not even start either...

buck boosting 5 volts to 12 is alot of electronics to run a fan so i would go with a molex installed on the case. i put one on my power supply so i could run a 5 volt and 12 volt LCD. i would go with installing one through the case rater than a card bracket think since those seems to clutter things up. if you dont want to cut then buy an Antec since the nicer ones already have a molex on the back.

Quote: Originally Posted by Sportbilly IIRC, transformers only work with AC voltages. There might be a way to do it electronically, but i'll be buggered if I know how. Your fans might put out enough air on 5 volts, then again they might not even start either...

i tested it through the USB and buggers barely spin

Quote: Originally Posted by carbongraphite buck boosting 5 volts to 12 is alot of electronics to run a fan so i would go with a molex installed on the case. i put one on my power supply so i could run a 5 volt and 12 volt LCD. i would go with installing one through the case rater than a card bracket think since those seems to clutter things up. if you dont want to cut then buy an Antec since the nicer ones already have a molex on the back

I would do that but i don't have any equipment at home to do it, and i'm sure ashell not dragging my PC to my school. so i'm just taking a PCI plate and the wires.

Well, since you can't hack on a case at school, have you considered some 5 volt fans instead? Delta has a list of them here:http://www.delta.com.tw/products/dcfans/search1.asp
Or, you can just buy a USB fan. Here's one for $3 : http://store.yahoo.com/giftsandgadge...sbminifan.html

i would like to make it my self. i've already made this but i guess i could make another from 5v fans. have they got the same sort of airflow rating as 12v?

any UK people know any places where i can get 5v fans?

You know haider, as long as you have a spare molex passthrough, what I suggested is not so hard to do, unscrew the PCI plate and the molex connector then you can take it wherever, hook it up to the power when you connect the USB backplate, and voila 12v USB-turned-in-to-power-plug port.

Quote: Originally Posted by TekXoID You know haider, as long as you have a spare molex passthrough, what I suggested is not so hard to do, unscrew the PCI plate and the molex connector then you can take it wherever, hook it up to the power when you connect the USB backplate, and voila 12v USB-turned-in-to-power-plug port.

now i'm real confused


what i meant by take it anywhere is, be able to plug it into any USB port without any modding and have the fans running full speed. this wont allow me to do that will it?

bare with me, i just had a 3 hour exam that didn't go 2 well so i'm a bit slow atm.

Quote: Originally Posted by haider254 .... bare with me, i just had a 3 hour exam that didn't go 2 well so i'm a bit slow atm.

Exams = yuk.

My worst exam had to be my final Business Studies A level: having had an English Lit. exam in the morning, I went to a pub for lunch - I got 2 pints in to save on legwork, then realised I didn't have an hour and 3/4ers 'till the next exam - just 15 minutes. I didn't want to waste the beer, so guzzled it, then realised that probably hadn't been such a great idea, so sunk another 2 pints of water.

I had to go for a whizz _five_ times during the exam ... the invigilators must have thought I was really taking the p155

Quote: Originally Posted by haider254 what i meant by take it anywhere is, be able to plug it into any USB port without any modding and have the fans running full speed. this wont allow me to do that will it?

The USB 1.1 specification calls for a supply of 500 mA (.5A) at a peak of 5.25v. This would be roughly 2.625W. At 12v though you're looking at .218A.

The average 80mm fan requires around 1.5W @ 12v or 125mA (.125A). So, using a very effecient transformer you could use ONE fan per USB channel. These must be seperate channels and not just two ports on the same channel or you'll overdraw the circuit. Another thing to keep in mind is that the specification allows for as little as 100 mA (.1A) per USB bus..... so, unless you want to build in a small circuit to test the available current and prevent overtaxing the USB bus, forget it.


BTW - you can also forget about using any other peripherals on the aforementioned USB bus as well.

All specs for USB 1.1 and USB 2.0 are available from USB Implementers Forum

Here's something I'd like to see included in a v3.0 USB spec: PoweredUSB

edit: errr.... messed up links.

thanks a bunch for the help guys, i think i'm gonna go with the molex on a PCI plate, gonna get that done soon, my teacher told me i can come in anytime during my "study leave" and do it.

Did you pass ur business studies then jon??

the only funny thin exam wise i've ever done is my GCSE RE exam, that was a joke, looked through it, wrote down some stupid answers about androids and sperm, popped my MP3 player in my ear (well not the player but the head phones ) and listened to that through the rest of it.

Quote: Originally Posted by haider254 ... Did you pass ur business studies then jon?? ...

Yup, it was a piece of p155