# Is this the right way to get 15 Volts out of PC Power supply?? Answered

So, Can i get 15 V out of Power supply if i wire +12 V to ground and -3V to ground and then pull a wire from the +12 to + on the device and -3 to - on the device.

Ex.

+12--|
Gr.----------------------------- +

Gr.----------------------------- -
-3----|

Gr.=ground
-=wire
|=means connecting something

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## Comments

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Follow steveastrouk's directions!!! Leave the GND connection out of the hookups, as the -3.3V becomes the new GND.

Voltage is the potential between 2 connections. Do you remember number lines from math? The distance between 2 numbers on a number line is the absolute value of each number added together (if they are on opposite sides of 0) or the absolute value of each number subtracted from each other (if they are on the same side of 0). So, since -3.3 and 12 are on oposite sides of 0 (GND), the total is |-3.3|+12=3.3+12=15. Since you are going between -3.3 and 12, you leave out 0 (GND) from your connections. See below:
-3.3 --0-----------12

If you were to connect the GND, you would blow the PSU.

Qa

I concur, it most likely won't have any effect on the circuit. Also, the amperage (current) will be limited to the weakest side, meaning that the lowest amount is what you could possibly use. If you were to use one side (+12 volts, for example) at 20 A(mps), and the other (-3.3 volts) at 6 A, you would only be able to pull 6 A maximum from your repurposed PSU. This is just a theoretical situation, your numbers may vary.

Ideally, you would want the 2 sides to be matched in current capabilities, but this is an imperfect world and it is hard for hobbyiests to match things from existing, repurposed items.

Qa