Can I use a second power supply for hard drives?

Question

I have an old Pentium-M based Shuttle PC that is great as a backup NAS solution at home, where I prefer low power consumption over speed.

It only has two SATA ports. However it has a PCI slot and I have a 4-port PCI card.

So my plan is this:

• Put the Pentium-M, PCI card, etc. into a case and let it use its native power supply (which is an external brick)
• Install a second 450W power supply in the case and use it to power 4 SATA disks. Their SATA connectors would then plug into the PCI SATA card.

To be clear...the second 450W would not be plugged into the Pentium-M's motherboard Only the HDD power (and maybe some fans).

However...would the second 450W power supply actually spin up? If I power it on, would it supply power to the hard drives, or does it need to be plugged into a motherboard to actually provide juice?

Solution 1

With the 450W power supply not connected to the motherboard, you'll need another way to switch it on.

You'll need to create a short between the PS_ON and Gnd pins on the power supply connector that normally attaches to the motherboard. Here is a guide. Hopefully your power supply has a switch on the back, then you just need to short the two pins on the connector, wrap it up with several layers of electrical tape, and use the switch on the back of the power supply.

Note, as already mentioned make sure the hard drives are powered on before you power on the PC.

Solution 2

Short answer yes.

Long answer, I once had a similar situation where I powered the mobo with one power supply and powered my SATA drives with another.

You'll want to power your drives up first or the mobo won't see them when it comes to boot.

Comments

[Zoredache]

They e-sata enclosures designed for this purpose. So yes, it certainly can be done.

[raindog308]

OK. I was concerned that the PS would need some sort of rewiring to start providing juice, since it's not plugged into a mobo and doesn't get a signal to "turn on" (other than its external switch).

[graf_ignotiev]

Oh right. I had my other PS attached to another mother board, but jmstoker's answer below addresses the issue.

[ganesh]

With SATA (and thus AHCI and hit plug capability) turning on the drives before booting the OS should not be needed. Still recommended though since it is the easy and always working way.

[Jamie Hanrahan]

Yes, it is needed. The drives won't be seen at all unless they're receiving power. There is no standby power to hard drives.

[Jamie Hanrahan]

I've run a two-PSU system for years. The right way to deal with a second PSU is to connect the green wires of the two PSUs' power harnesses together. This is indeed the PS_ON signal from the motherboard to the PSU. Now, when the mobo asserts this signal, both PSUs will receive it and will power on. A fancier method is to connect the coil of a 12 volt relay to the +12 and ground of one of the drive power connectors from the main PSU. Connect the normally open contacts of the relay to the green wire and any ground wire of the new PSU. But this isn't necessary.