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+5VSB: a waste of power?

Posted: Thu Dec 20, 2012 1:58 am
by edh
I've recently got hold (for free!) of an old system from a friend based on an AS-Rock K7NF2 motherboard. On it it has a jumper called PS2_USB_PW1. I've never noticed one of these before but from what I've read it controls whether or not +5VSB is used to power devices while the system is in soft off. This can be used for things like Wake-on LAN which I never use.

Soft off power consumption has often been mentioned here before and measuring this system came to 7W. Disabling this jumper brought the number down to 6W. The margin of error may be +/-1W but I have repeated these measurements several times switching the jumper back and forth and it is quite consistent, I can say that using +5VSB to power devices while the system is off wastes power.

Now, assuming that other motherboards may have such a jumper setting, is it worth comparing the effects of this on different boards? Imagine how many systems this effects across the world and the potential power savings add up! Maybe I have solved the impending energy crisis. :lol:

I am going to check other systems I have for similar settings and try and minimise the soft off power where possible.

Re: +5VSB: a waste of power?

Posted: Thu Dec 20, 2012 2:41 am
by nutball
It also powers USB devices that can be used to wake the system, for example keyboards. I have my system set to resume from S3 sleep at the press of a key - I couldn't achieve this without +5VSB. For the sake of 1W I think I can live with this. Each to their own I guess.

Re: +5VSB: a waste of power?

Posted: Thu Dec 20, 2012 2:56 am
by edh
nutball wrote:It also powers USB devices that can be used to wake the system, for example keyboards.
Yes, that's where I guessed it was going.

I have tried resume on keyboard or mouse but I found it too easy to set off accidentally. Keyboards sit on desks and they're easy to knock so its not suitable if you use your desk for other things too. As you say each to their own but I find the power button serves me fine. ...and it's not just 1W, it's 1/7 of the power! :wink:

Edit: How many people use wake on keyboard? Added a poll to the original post to see where other people lie on this and whether there is power to be saved.

Re: +5VSB: a waste of power?

Posted: Thu Dec 20, 2012 4:46 am
by Vicotnik
Usually I have my system set to go to sleep after a time of inactivity. It's nice to be able to wake the system by pressing a key. When I shut down my system manually I afterwards switch off the power strip that powers everything, to reduce wasted power.

Re: +5VSB: a waste of power?

Posted: Thu Dec 20, 2012 9:22 am
by CA_Steve
My system wakes on mouse click. System sleeps/hibernates at ~1W. Soft off is <1W. It's down in the mud for a P3 Kill a Watt's accuracy. Tested with a Corsair HX520W and a Seasonic X-560.