USB power supply?

sureno · #1 (**permalink**) 4th September 2008 , 08:33 PM

i recently acquired a laptop cooler. this unit is powered by usb, was thinking could i use my iphone charger to power it if i detach the cable and replace it with a normal usb? the plug itself outputs 5v so??? just want confirmation, can't see why it wouldn't?

Stagesound · #2 (**permalink**) 4th September 2008 , 11:16 PM

sureno - What do you mean by iPod charger? Is it a 13A plug "wall wart" type with a USB socket for your iPod lead? Are there any ratings on either device? I have a USB power supply which I use for various things, and the rating is 5V 1000mA. Voltage is always going to be 5V but current capability will vary.

Any USB device which is designed properly should not draw more than 100mA without negotiation, and since the spec. for USB hubs allows for devices which can only supply 100mA (though most will supply much more) it would be good design practice to try and keep the current to 100mA max. So in theory, any properly designed USB power source will deliver at least 100mA, and any properly designed load will take no more than 100mA without negotiation - and if it can't negotiate up, it will just not work. (But will do no harm).

Having said that, there are quite a few devices about which pay no attention to standards and do their own thing. (Some of the better devices which require more current actually use two USB cables, so that each port on the supply gives only half the current). I can't imagine however that the little fans in your cooler will take more than 100mA, so you should be fine. (Some coolers have a USB through connection, or even a USB hub, which would suggest they are drawing very little current themselves.

If you want to be completly certain, you need to ensure that the iPod charger has a rating higher than that of the cooler - hopefully they'll have either current or wattage ratings on them somewhere.

sureno · #3 (**permalink**) 4th September 2008 , 11:19 PM

the wall wart is 5v 1A. i will try it, just didn't want to risk frying it. btw thank you for the detailed reply

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#1 (permalink) 4th September 2008 , 08:33 PM
sureno Forum Idol Join Date: Jul 2008 Location: west london depot Posts: 7,599	USB power supply? i recently acquired a laptop cooler. this unit is powered by usb, was thinking could i use my iphone charger to power it if i detach the cable and replace it with a normal usb? the plug itself outputs 5v so??? just want confirmation, can't see why it wouldn't? ______________________________ Where is the chase and how do I cut to it?!? WWW.SURENO.CO.UK www.myspace.com/djsureno http://twitter.com/djsureno
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#3 (permalink) 4th September 2008 , 11:19 PM
sureno Forum Idol Join Date: Jul 2008 Location: west london depot Posts: 7,599	the wall wart is 5v 1A. i will try it, just didn't want to risk frying it. btw thank you for the detailed reply ______________________________ Where is the chase and how do I cut to it?!? WWW.SURENO.CO.UK www.myspace.com/djsureno http://twitter.com/djsureno
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#2 (permalink) 4th September 2008 , 11:16 PM
Stagesound Senior Member Join Date: Jul 2008 Location: Northern Ireland Posts: 181	sureno - What do you mean by iPod charger? Is it a 13A plug "wall wart" type with a USB socket for your iPod lead? Are there any ratings on either device? I have a USB power supply which I use for various things, and the rating is 5V 1000mA. Voltage is always going to be 5V but current capability will vary. Any USB device which is designed properly should not draw more than 100mA without negotiation, and since the spec. for USB hubs allows for devices which can only supply 100mA (though most will supply much more) it would be good design practice to try and keep the current to 100mA max. So in theory, any properly designed USB power source will deliver at least 100mA, and any properly designed load will take no more than 100mA without negotiation - and if it can't negotiate up, it will just not work. (But will do no harm). Having said that, there are quite a few devices about which pay no attention to standards and do their own thing. (Some of the better devices which require more current actually use two USB cables, so that each port on the supply gives only half the current). I can't imagine however that the little fans in your cooler will take more than 100mA, so you should be fine. (Some coolers have a USB through connection, or even a USB hub, which would suggest they are drawing very little current themselves. If you want to be completly certain, you need to ensure that the iPod charger has a rating higher than that of the cooler - hopefully they'll have either current or wattage ratings on them somewhere.
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