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# If you connect the 12Vdc and -12Vdc on a desktop PSU do you get 24 Volts? Answered

I used to understand more about electricity and electronics, i swear.
I have used the yellow-to-red (+12 to +5 Vdc) method to create 7 volt dc connections for my desktop and xbox fans. I understand the concept of differences in voltage.
Do these concepts carry over into negative voltage available on the ATX power supplies?

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## 4 Replies

kelseymh (author)2011-04-11

Yes, they do! "Zero volts" is an arbitrary state, but it needs to be defined consistently for a given application. That is, whatever part of your equipment (usually the chassis) you decide to set to zero volts, must be set that way in all parts of your circuit.

In particular, if your power supply is connected to the wall, then your chassis ground needs to match the ground on your power cord. Otherwise, you'll be in for a

... wait for it ...

nasty shock!

>ba-da-bing<

steveastrouk (author)2011-04-12

Yes, up to the current limit of the smaller rated powersupply, so a typical -12V is limted to 0.5 A, that's the maximum current you can get, not the 20A off the +12.

Andale_The_Great (author)2011-04-12

Ah, you bring up the best point of all these. I am not planning to actually use it in this way but I wanted to know for possible future applications.

NachoMahma (author)2011-04-12

. As long as the two supplies use the same reference point for 0V (every desktop PSU I've seen does), then yes. You are measuring differential voltage, so VOut = V1 - V2.