Wiring a USB Fan

[iaino2002]

Hi, recently the cabinet that I house my ps3 in has been getting pretty hot so I thought i would see if theres a way i can install a fan at the rear to extract the warm air away while drawing in fresh.

What I had in mind was buying a 20cm computer case fan and then wiring it to one of the ps3's USB ports, so that it only comes on when the ps3 is switched on.

Only problem is most of those fans are rated at 12V and USB only provides 5V. Now my question to you, the electronics community, is there a way I could use 2 usb cables to provide 10V to the fan. I would need a way of ensuring that no voltage is back fed into the ps3, i was thinking a few diodes or a bridge rectifier perhaps would do this.

I will only be using the +5V and ground wire on each of the USB cables for this.

Many thanks in advance, Iain

 

[donkey]

just a quick note on this, you COULD do all of that hard work and then try to configure the air flow to be just right, or you could simply type "ps3 fan" into google and buy a product prebuilt for around $15. just a thought

 

[iaino2002]

Yep, i had looked at the specially made ones, however they are all designed to get more air through the ps3 itself, what i'm trying to do is cool the cabinet the ps3 sits it, I don't really think they'd be suitable for my needs, and seeing as they all run on small diameter fans they're probably quite audible.

 

[iaino2002]

Could anyone point me in the right direction of how i'd go about doing this, i'm hoping it'll be a nice little mod if it works, seeing as i have the stuff lying around anyway,

Thanks

 

[timothy48342]

I think all the +5 contacts on the whole usb system are conneted to each other (and all the grounds as well) so this would be like hooking 2 sets of wires to one 1.53v battery and hoping to connect that battery in series with itself to get 3v. Not going to happen. (I did try that as a kid. Lots of wires, lots of diodes, lots of time, no success.)

It might be possible if internally there were 2 seperate usb systems. ("Might!" that is, but only if the designers isolated each system from the other.) Somehow I think that all the grounds of all the usb channels are conneted, so I can't think how it could work.

What about getting a 120VAC fan that really packs a punch and plug it into the same power strip as your ps3. Then when you turn on the power strip, both the fan and your ps3 come on together? (as well as your dispay and everything else.)

--tim

 

[iaino2002]

Thanks for that explanation tim, I wont bother trying that method. Although your AC fan approach gave me a sweet idea. I could use an AC fan wired to a contactor with the 5V from the usb socket providing the switching signal. As i probably wouldn't want the fan on when watching a film on my laptop for example, this way the fan will only come on with the ps3, but with the benefit of AC power. I assume that won't place any excess load on the usb bus?

 

[jackorocko]

No you can not add two 5V usb wires together and get 10 volts. They are all connected to the same supply source.

I assume that won't place any excess load on the usb bus?

Not as long as you isolate the two souces. A relay is a form of mechanical isolation and would work perfectly well in this situation.

 

[donkey]

i had a chord for my usb 3g modem that had 2 USB a plugs and a mini usb, the information in the booklet said that extra plug was used to provide extra power, I am assuming that means current right?

 

[timothy48342]

An extra usb plug alowes a device to draw extra current, yes.
Assuming 500mA available per port... (Don't know if that is always true)
500mA per port times 2 ports for a total of 1A.

But the manual isn't wrong to say extra power instead, since the voltage value doesn't change. 500mA at 5V is 2.5 Watts
2.5 Watts per port times 2 ports for a total of 5 Watts.
-t