USB voltage

TBirdUK · 13 Oct 2007 at 20:31

What voltage is supplied to a USB port?

Cheers

paradigm · 13 Oct 2007 at 20:48

TBirdUK · 13 Oct 2007 at 21:00

Is it always 5v? I want to run a couple of USB fans in a car but its 12v, probably will knacker them connecting them straight to the battery.

Cupra · 13 Oct 2007 at 21:03

get a resistor? what fans are they

paradigm · 13 Oct 2007 at 21:07

TBirdUK said:
Is it always 5v? I want to run a couple of USB fans in a car but its 12v, probably will knacker them connecting them straight to the battery.

You can get Cigarette Socket to USB adapters, which I assume MUST bring the voltage down to 5v from the car's 12v.

You could either run the fans from one of those, or take it apart and use the wiring to give you your 5v USB socket from any 12v source in the car.

TBirdUK · 13 Oct 2007 at 21:25

Sounds like a good idea, need them near a fridge in a van so no cig lighter socket - just rip it apart should to the job - thanks. I thought about just putting in one of those pci blower things - do they work off 12v then?

Werewolf · 13 Oct 2007 at 21:51

IIRC USB can provide both 5 and 12v.

TBirdUK · 13 Oct 2007 at 21:55

So how do I find out if I can just cut the usb cable off a couple of fans and wire them directly to 12v?

paradigm · 13 Oct 2007 at 21:56

Werewolf said:
IIRC USB can provide both 5 and 12v.

Not according to the datasheets I have for USB.

4 pins

5v VCC (red)
D- data- (white)
D+ data+ (green) (signalling volts of 2.8-3.6v)
0v GND (black)

Infact I'm sure the specification for USB states that it will not provide more than 5.25v (5% tolerance)

EDIT: There is the PoweredUSB standard that can provide 5v, 12v or 24v, but you would know if it was a PoweredUSB as the plug has an extra row of 4 pins.

PoweredUSB Port:

ns400r · 13 Oct 2007 at 21:58

USB is 5volts !

Priapus · 13 Oct 2007 at 22:54

ns400r said:
USB is 5volts !

We know, we got the picture.

Munromax · 13 Oct 2007 at 22:57

USB is 5 Volts

Well maybe 5.25

However, FireWire is 8 - 30 Volts :eek:

Energize · 13 Oct 2007 at 23:05

Yup, nominal voltage is 25v so allows it to power all external hard drives. Whereas with usb lots of them need external power sources.