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# Atx supply possible Wattages Answered

Hi there community, i have a very certain question.
I recently modified an atx supply of 420W. Some of its features are :
5V 32 A

12V 14A

3.3V 22A
-12V 0,5A

Lets say i connect one end to 5v and the other to -12v, what wattage will this give me ? Probbaly not 17x32=544
Is bridging possible? What are the possible wattages ?

Thank you for your time :)

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## Discussions

Thank you for the answers kind strangers !
My basic question was the one you both answered. Maximum amperage is therefore the lowest available from a rail, got it

Correct. Essentially you can't get something for nothing.

The numbers for current, printed on the nameplate of your power supply, represent the maximum current that rail can comfortably supply.

The actual current drawn by a load, depends on the character of the load.

Anyway, you asked about a hypothetical load, connected between the +5V rail and the -12V rail. What is the maximum current that could comfortably be supplied to this load?

The answer is 0.5 A, because that is the maximum for the -12V rail.

How much power dissipated by this hypothetical load with 17 volts across it, and 0.5 amperes, maximum, flowing through it? Answer: a maximum of (17 V)*(0.5 A) = 8.5 W

By the way, the people who sell power supplies, often try to make the numbers seem big, because big power is sexy, obviously.

I was expecting the number 420 W, to be the sum of all those individual rails, supplying the maximum rated current.

Specifically:

(5V*32A)+(12V*14A)+(3.3V*22A)+(-12V*-0.5A)

= 160W +168W +72.6W + 6.0W

= 406.6W

which is close to 420W, but not exact. I dunno. Maybe they rounded it up to 420, because that number sounds good?

Final note: I do not grok this thing you call "bridging". I just do not get what you are asking about that. So I cannot say if that activity is possible to do that, or not, with your power supply.

I have heard of "planking", but I think that is something different than "bridging".

;-)

What i mean by bridging is a process available in common transformers where wiring them in different combinations provide different voltages or amperage. But i suspect this is not possible( asked to be sure).