Two PSUs in one box

[deimos3428]

I currently have Antec Earthwatts 500, and for the record it works great for my needs.

However, it doesn't have a lot of PCIe power connectors and someday I'd like to crossfire my 4870. I'm quite sure it's easier to just buy a larger power supply with enough connectors, so this is more of a theoretical question.

Assuming I have the physical space, is there anything dangerous/harmful/just plain wrong with using a second Earthwatts 500W PSU to power some of the additional components? Curious to know if there would be grounding/ground loop issues or things of that nature.

 

[HOOfan 1]

It is possible yes, they sell special ATX 24 pin cables/extenders that allow two PSUs to get a power on signal at the same time.

The Earthwatts 500W is group regulated though, so it might not work too well if you just try to power compontents that utilize only a single voltage. For instance, it might not work too well if you try to just use it only for PCI-E connectors, you would want to plug in perhaps some SATA drives to use at least some 5V power.

 

[brblx]

i would think something like a 300w seasonic (or the similar antec 380) with a fat 12v rail would be more than adequate to run a hard drive and a video card. should theoretically work if you really have room for another full size psu.

it wouldn't be that much cheaper (maybe 40 for the psu, 10 for an adapter) than just buying an EA650 ($70?), though. really you could probably xfire on the EA500 with a pcie adapter if you wanted, though you might be pushing the limits of that psu at times.

 

[Modelworks]

You have to be careful on what supplies you mix and in what way they connect with each other. If two supplies were to have their+12V connected then you can get a situation where regulation goes crazy. The power supply is no longer measuring its output but also the output of the other supply to determine whether it needs to boost or cut the output voltage. If supply A cuts its voltage, then supply B will raise its voltage to make up for the difference, which could make supply A cut back even further. Supplies that are made for multiple PSU installs already have a circuit to prevent voltage from being able to re-enter the supply and effect the regulation.

You could add that to a supply using a diode, but that will cause a drop of .6 volts DC on the output that the supply will not make up for.

 

[Billb2]

No problem. Many benchmarkers use two PSUs. One for the CPU and one for everything else.

 

[theAnimal]

If you're not OCing heavily or have a ton of HDDs, your PSU should have no trouble with a 2nd 4870.

 

[JEDIYoda]

Originally posted by: theAnimal
If you're not OCing heavily or have a ton of HDDs, your PSU should have no trouble with a 2nd 4870.

read and comprehend much?? rofl.....answer the question....rofl

Assuming I have the physical space, is there anything dangerous/harmful/just plain wrong with using a second Earthwatts 500W PSU to power some of the additional components?

 

[amenx]

There are PSUs specifically designed to be used with another PSU. Such as those dedicated GPU drive-bay units by Thermaltake:

http://www.thermaltake.com/pro...ePower/w0130/w0130.asp

 

[PM650]

Running two power supplies can and may work very well, but the vast majority of the adapters that allow them to power on simultaneously do only that, and nothing more (including the aforementioned TT psu). If the secondary power supply that isn't connected to the mobo encounters a fault, it will shut down and the primary will continue to operate; I don't want to be the one around your pc when suddenly only half of it is powered.

 

[deimos3428]

Thanks for all the informative responses guys. I hadn't considered the power connector/switch on the motherboard. Is there any signal flow between the motherboard and the PSU when the power switch is flipped? (I always thought components were "dumb" and just drew power, so long as the master switch on the PSU they were connected to was on.)

 

[HOOfan 1]

not all PSUs even have a power switch. The 5sb power is always flowing on the PSU though, unless the switch on those PSUs that have a switch is turned off...or it is unplugged from the wall.

 

[PM650]

PC's used to be dumb and just power on back in the AT days with the front switch connected to the mains, however later AT mobos also supported ATX power connectors & momentary front power switches (what we use today). Modern pc's tell the power supply to turn on by driving the PS_ON line (green wire) to 0V, the supply turns on and later drives the PWR_GOOD line (gray wire) to 5V after the voltages have stabilized, after which the pc actually turns on.

 

[mr3manuel]

There is something else you can do to power up extra drives using a second PSU...

on the 24 pin connector just connect a switch from the green(power on) cable to any earth(black)
the second power supply can be mounted inside your case with an external switch but to avoid conflicts and power issues obviosly ONLY CONNECT TO EXTRA DRIVES

the crappy part of this setup is that you have to remember to power up the second psu before actually turning your machine on

I've been using a similar setup for years when connecting and testing car audio systems without a car of course