![]() This can be hazardous IF the equipment has any other ties to the casing or other true ground sources, but these fans are all plastic so that isn't an issue. Since the 12V is measured with respect to where ground is, if we raise ground by 5V, then the "12V" line is now only 7V above the new "ground". Waldosan - what he is doing is technically raising the ground voltage up by 5V. A better analogy would be moving the ground from the negative of the fourth battery to the negative of the third battery - which would give you 9V since you have raised the ground plane up by 3V. In your scenario with the batteries, you would get 6V. Now, if you switch the ground to one of the lesser voltage rails, such as the 12vrail+5vrail, you end up providing 7v, which is the popular 7v fan mod These rails are not true voltage rails, they are accessed by using one of the real voltage rails instead of the common ground as a ground for that rail, so the 12v=12vrail+ground, 5v=5vrail+ground, and 3.3v=3.3vrail+ground. While these rails are common knowledge, many people don't know that there are also several "virtual rails", the 8.7v, 7v, and 17v, as well as the 24v and 15.3v rails. anything that is an 80+ will handle it no problem, if you dont have an 80+ you are asking for problems with or without this mod quote from tech powerup: average computer has a +/-12, +/-5, and 3.3v rail, and it is simple to power fans off of these rails by changing the power lead for the fan from the normal 12v to the 5v rail, as most fans won't start with 3.3v. ![]() There is such a thing as a negative voltage, basically its like having a bunch of batterys in series, then you flip one around so instead of 3v + 3v + 3v + 3v = 12v, you flip one around and it acts as a negative voltage so + 3v + 3v + 3v = 9v if you have a descent quality power supply this wont be a problem.
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