Too many PSU adapters?

linker500 · Feb 12, 2018

Okay, weird situation.
I have a bunch of old computer parts from my last upgrade, with a micro atx board, so I wanted to make "meh" portable computer. Usable.
I just needed a power supply
So I dug out my first desktop computer (2008-ish crap dell), and now have a passable psu.

The main issue is that it doesn't have a PCI-E power connector.
I have no onboard graphics, and the old gpus I have lying around are 6 pin.
So I did some more digging to find that I have a molex to 6 pin adapter.
...but the psu doesn't have any molex connectors.
So I am considering buying a sata-power -> molex, to then connect to a molex -> 6 pin adapter.
Any issues with this solution?
Definitely not my first choice. But if it works...
Might save me a bit of money.

geofelt · Feb 12, 2018

What is the make/model of the psu?
I can't imagine that there is a psu without a molex power lead.
What does the data plate say about watts or amps on the +12v rails?

What are the graphics card/s in question? I suspect that they might be old and power hungry with a need for 6 pin power.

Barty1884 · Feb 12, 2018

I wouldn't.

Obviously, you haven't stated much about the PSU itself - but it doesn't sound good.

Generally, if you need an adapter to run a GPU - you *actually* need a new PSU. That's doubly true when you're talking about daisy-chaining adapters. That's just asked for trouble.

Considering a decent enough PSU can be had for ~$20 (not great, but definitely a decent enough unit).....
PCPartPicker part list / Price breakdown by merchant

Power Supply: EVGA - BT 450W 80+ Bronze Certified ATX Power Supply ($21.99 @ B&H)
Total: $21.99
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-02-12 13:07 EST-0500

Again, it's hardly the best PSU even made, but it's going to be a substantially better idea that adapters as described.

linker500 · Feb 12, 2018

geofelt :

The card is a 550ti. Got it cheap on ebay a while ago.

Barty1884 :

I have no idea what the power supply is. It was in a dell premade desktop. Nothing exceptional, but at least its not a shady $5 chinese one.
I am really trying to save money on this project, already spent more than I'd like. But I will consider the option, if I can't find any other psu.
Any specific reason daisy chaining adapters is bad though? The only thing I can imagine is inadequate power delivery to the gpu.
I'm not considering doing it at this point, but I am still curious why it is a bad idea.

Math Geek · Feb 12, 2018

linker500 :

that is exactly why you don't want to use those adapters. they may provide the needed connection but they do not change the available power. you can daisy chain a single molex into a dual 8-pin pcie connection but that does not mean you're gonna get 300w out of those connections!!

a molex connection does not provide the 75w that a 6-pin is supposed to. you could combine 2 x sata into a single 6-pin and if the psu has the available power, which is highly unlikely from an old premaid psu, then it would actually provide the needed 75w from the 6-pin. but again it is unlikely the psu can give all that power as well as power the cpu, mobo and other parts it has to power as well.

Barty1884 · Feb 12, 2018

Can you take a pic of the labelling on the PSU?

While it may not be a "shady $5" PSU, that doesn't make it "good" in any way, shape or form.

Dell uses various suppliers - Delta & ACBel, generally these days, but there was likely others ~10years ago..
Given the age/era of the unit though, it's probably labelled in the 300-400W range.... Add degration over time, and the potential that it wasn't great quality to begin with, it can likely do nowhere close.

As for "why", I'd be most concerned with the SATA power cable in the equation, although Molex adapters aren't ideal themselves.

From memory, a SATA power cable has 3x 12V wires, rated for a (theoretical) max Amperage of (something like) 7A. In practice, even the most power hungry SATA devices are ~15W, so I don't know if they're even implemented capable of greater than a couple of Amps.
Molex, again theoretically can do much more.... 20A (i think, again, from memory)

550TI's vary in power draw dramatically. I think there were ~110W TDP options..... then there were cards like the Zotac AMP! that could draw >250W at load.

Working it back from the >250W cards.... 250W draw - 75W from PCIe slot = 175W. 175/12V = 14-15A.
All of that coming from a SATA power connection that's rated for about half of the power draw at absolute 'best' case....... You may well be looking a fire hazard, assuming the PSU doesn't just 'give up' given it's age and potential quality.

geofelt · Feb 12, 2018

You are not likely to work.
While dell power supplies are not exactly cheap, they will have only sufficient power to run the originally installed components.

Look at the data plate, a requirement for UL power supplies.
In particular, look at the +12v amps/watts.

Daisy chaining adapters works, I have done what you describe to test out a graphics card.
But, the underlying power supply must be strong enough.
If it is not, you risk overloading the psu and causing damage to anything it is connected if it fails under load.

linker500 · Feb 12, 2018

Barty1884 :

Oh yeah, not at all willing to bet my main hardware on that psu. I am putting minimal faith into the unit.
I'll try and get the info on the power supply when I have access to it.

My current plan is only to test the cpu, ram and motherboard with it. I just need it to boot. I have a reaaallly super old gpu that doesn't need a power connector, so I should be able to make sure it at least posts with that.
The cpu is only 65 watt I believe. Although, I'll pass the specs by you guys first before I try anything else.

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