how to connect 2 P.U. ?

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I need to add some power to my PC.
Here is how he is right now :
ZNF3-250Gb Pro chaintech motherboard with a Athlon 64 3200+ and 3Go of
Ram. The graphic card is a noname ATI Radeon 3600.
All is encloseed in a Lian Li V2000 (v.1) tower.

I will have to add a Sapphire HD 3850 which require to connect 2 molex
connector and add 2 more HDs.

My actual Power Unit is up to 350W. I have a spare 200w PU from my old
Will this be enough for my new configuration?

MY issue is : how to connect the 2 power unit so WHen I stop the
computer, the second PU will stop like the 1st one, knowing that the
2nd PU will not be connected to the Motherboard?

Thanks for your advice.

Re: how to connect 2 P.U. ?

Henri Beyle wrote:
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This doesn't work.

There are computers with two power supplies, but those are specialized
units that hve them set up as hot spares. They cost probably (at least)
eight times what your PC cost.

Buy a new and bigger power supply, at least 650 watts.

Re: how to connect 2 P.U. ?

Henri Beyle wrote:
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My guess is, that is a S754 motherboard.

You can get power numbers here. The HD 3850 is 63W, or roughly 12V @ 5A.

You could look at the 12V rail on the 350W power supply, and see how many
amps are available. Then do a budget, to see whether the amps available
are enough.

Disk drive 12V @ 0.6A
CDROM      12V @ 1.5A   (only when media is in the CD drawer)
Processor  12V @ 8.24A  (89W/12 * 1/0.90 = 8.24A assuming a 90$ efficient Vcore
Video      12V @ 5A

So probably at least 12V @ 16A, or more.

There is also a total power calculation you can do, since that has to
be checked as well.

The HD 3850 does not need a lot of amps on the PCI Express 2x3 connector,
so you don't need fancy or heavy wires for that.


To connect two ATX power supplies to the same controls, you hook two black wires
together. The grounds need to be common. You hook the two PS_ON# wires together.
Those are green in color. The motherboard circuit driving PS_ON#, has to be able
to drive two loads when you do that.

You can get specs here. These will help you figure out the wires and colors,
for PS_ON and COM, on the main connector of each supply.

    Main                        (green)               Main
    Coonector     PSON# <--------------------> PSON#  Connector
    Supply        COM   <--------------------> COM    Of
    To                          (black)               Second Loose supply

Strip the insulation off a portion of the green wire on each PSU.
Run a wire from the PS_ON wire on one supply, to the other. The
PS_ON# are now in parallel operation.

Do the same for one COM wire on each harness.

One power supply connects to the motherboard, the other remains disconnected.

When the motherboard turns on the PS_ON# signal, it will
go to both power supplies.

I do *not* recommend this method, but if you need to know
how to do it, that is how you do it.

Buy a power supply of sufficient capacity, so that no
accidents can happen. That is the best solution, and
takes no additional space.


Re: how to connect 2 P.U. ?

Paul a exposť le 12/06/2009 :
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Thanks for your very complete response.
Now I know how to do it but I won't if you tell me it's not
I'll buy a more powerful PSU.

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