+12, -5, = +7. or does it?

[Stree]

Can someone give a definitive answer to this one please? I do not know enough about electronics to have an opinion either way, but I hear on various forums that by utilising the +12v cable along with a -5 v cable and a ground, you effectively have a +7 volt supply to undervolt fans with, hence slow them down. Is this a fact or wishful thinking?

[Cyäegha]

I you used +12V and -5V lines, you'd get 17V. You need to use the +12V and +5V lines (yellow and red wire respectively).

edit: Here's a link to an old SCR article on the subject.

edit again: There are also plenty of posts on the forum - search for "7V trick" for instance.

[Stree]

Thanks for that, I will have a look at the link.