Newbie question regarding wire voltages.?

[Peter7777]

I currently have a wire running a 5 volt current to power a fan. If I strip this wire running the 5 volts somewhere in the middle, and solder another wire running 12 volts onto the the stripped portion of the original 5v, will this result in 17 volts of total power traveling up this one wire to the fan, or does the 12 volts simply over-ride the 5 volts; resulting in just 12 volts of power running up instead of 17, even though the 5 and 12 volt supply are being run up a wire?

 

[Stephen P]

>If I strip this wire running the 5 volts somewhere in the middle, and solder another wire running 12 volts onto the the stripped portion of the original 5v,

You would short the 5 volt & 12 volt lines together. This would be very bad. Depending on the design of the power supply it would probably either burn out or shut down.

 

[classicsat]

If you parallel the supplies, the higher voltage supply (12V) will simply overtake the low voltage (5V) one. If it is not set up correctly, the 12V could blow out the 5V supply, or any loads that only take 5V.

To get 17V, you need to hook a 12V supply (which is isolated from the 5V supply), in series with the 5V supply.