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 Post subject: October 2009 - DIY Question
PostPosted: Wed Sep 30, 2009 7:06 pm 
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Question about he Power Everything with USB part of the article. I was thinking about making a laptop stand with two case fans powered by USB, but I was not sure if you could put two fans onto the same connector. I wasn't sure if the draw would be too much on one plug. It would be cleaner to have 2 fans taking up only one USB if possible.

Thanks


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PostPosted: Thu Oct 01, 2009 2:27 am 
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add up the 2 fans current draw, it should be listed on the fan. you have (probably) 500 ma to work with.. many laptop USB ports are less however - 250 ma in the case of my old compaq. also some smarter USB ports will limit to 150 ma (think its 150) without the proper signaling.

if its a 12v fan at 180 ma, it will be 75 ma at 5v (close enough anyway, varies with load).


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PostPosted: Thu Oct 01, 2009 7:29 am 
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http://www.newegg.com/Product/ShowImage.aspx?Image=11-998-109-03.jpg&S7ImageFlag=0&WaterMark=1&Item=N82E16811998109&Depa=1&Description=APEVIA%20CF4S-UBL%20Case%20Fan

That's the fan. Looks like its' 12v @ .25A, so 2 would be right at the 500 ma/.5A line. Do you think I should try it?

AJ


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PostPosted: Thu Oct 01, 2009 9:24 am 
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each will only draw about 100 ma at 5v. (5v is 42% of 12v so 100ma is 42% of 250 ma.. give or take)

real issue is will the fan start at 5v.. some 12v fans will, some wont. some need 6 or 7 to fire up. once spinning they can run on less but you are limited to 5v period.

no way to tell in advance unless they list it, sorry.

EDIT they do list it here - those are a no go.

Quote:
Start-up Voltage 6 VDC


quick look shows most APEVIA 80, 120, and 140 fans need at least 6v to fire. didnt check em all but they all look like the same design within a size, just different colors/LEDs etc.

unless you dont mind starting them spinning by hand till they hit speed :D


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PostPosted: Thu Oct 01, 2009 4:14 pm 
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My antec tricool fans start at 5v It says so in a warning about using a setting other than "high" when using a fan controller.





Ted


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PostPosted: Mon Oct 05, 2009 6:01 pm 
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So is there a way to do two fans? Or should I just attempt one? Or should i just go for a totally different fan?


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PostPosted: Wed Oct 14, 2009 11:59 am 
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CTskifreak wrote:
So is there a way to do two fans? Or should I just attempt one? Or should i just go for a totally different fan?


I did a comment some time back on the article with a focus on using USB to power things and making the barttery charger. That post can be found here .

The problem based on some experiments I have done is that 12 Volts fans don't move much air at all running on 5 Volts. Many will not even start at 5 Volts. However with a bump they will turn once started. Overall I am not real big on connecting things like fans to a USB port for power as sometimes real bad things can happen.

If you really want to try it then I would suggest starting with a single fan. Good luck finding a fan designed to run on 5 Volts though I mention a few manufacturers in my post I linked to.

To test what you decide you could get 5 Volts from a desktop and test your fan(s) using that 5 Volts just to see what you get for airflow. Snag the 5 Volts from an unused molex connector for a drive or something like that.

Ron


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