What current can an 8 pin pci-e cable deliver?

[JonJ678]

Assuming the rated 12V, four earth lines. What current can it reliably handle before the wires run too hot and it all goes terribly wrong?

I can't find the specification for this online, so currently my only option is to cut one of the cables off and try to work out what gauge it is. I don't want to do this, so hopefully one of you knows where I can find the answer.

Many thanks

Jon

 

[vertica]

http://www.allpinouts.org/index.php/PCI_Express_(PCIe)_6pin_power

This suggests 8Amps per circuit for the 6pin.

An 8pin header just has an additional two ground wires. Assuming that the '8A per circuit' is correct and refers to the ground cables, then the 12V cables must be rated for at least 13.3A (5 grnd @ 8A split between the 3 12V supplies). But that would give a massive theoretical power output from each connector, and the guage looks far too small, so i can't confirm this.


EDIT: Appears that the above could be wrong, as i've found this on another forum:

The 8-pin specification came out well after the 6-pin spec was released. The original 6-pin spec called for a maximum current throughput of ~2.08 amps per +12V line. The 8-pin spec provides a maximum of ~4.17 amps per +12V line.

So, when they made the new connector spec, they made it physically different so that users with older power supplies would not install video cards which potentially try to pull 2x as much current through the wire as the power supply was designed to provide.

They could have used any sort of physically different connector, provided it was rated to be able to cope with the correct amount of power.

I don't know if I explained that very well. My apologies if not. Paul is much better with the PSU questions...

But again no references or confirmation so is to be taken as is, however this gives a more realistic power throughput.

 

[JonJ678]

allpinouts.org has one for the 8 pin as well, looks like you're right regarding number of 12V lines.

I'll keep looking for a source, may have to start emailing psu manufacturers. Thanks for your reply, 12A per 12V line sounds like the right order of magnitude, I'll work with 140W as an approximation for now.

Cheers

 

[95thrifles]

Jon

Check this out, should answer your questions

 

[JonJ678]

That is an extremely informative website, thank you very much.

Summarising for anyone who comes across this thread, the 8 pin PCIe cable is good for 150W, the 6 pin for 75W. Obviously this doesn't mean that the power supply is able to supply 2 or 4A down each 12V line, just that the cabling can cope.

Cheers guys

 

[fornowagain]

Summarising for anyone who comes across this thread, the 8 pin PCIe cable is good for 150W, the 6 pin for 75W. Obviously this doesn't mean that the power supply is able to supply 2 or 4A down each 12V line, just that the cabling can cope.

That's the official PCI-SIG rating, not what the cable/connector can handle. The actual current capacity is way higher and depends on the operating temperature, number of connections/material and the cable gauge.

If you take a typical 6 pin .165" mini-fit molex (PEG plug). For example, with 6 connections it's 4A per circuit (3x12v and ground) at 30C AWG22, so 12A. That's pretty thin wire btw, depending on the psu, but 18 or even 16 AWG is common for PCI-E cables. With more connections and thicker cables they de-rate per circuit.

Although what's I've always found quite odd is the PCI-E 8pin still only has 3x12v conductors, so it can't actually handle more current.

 

[JonJ678]

Returning to this thread solely because I'd lost the above link I find a better one still, thank you for your reply fornowagain. I'm afraid I didn't notice it at the time (rarely frequent this forum).

The application I have in mind should draw around 9.5A at 12V, but I really need to spend some more time on the calculations. I'm looking at running multiple pairs of peltiers in series off the 12V line using the pci-e cabling, this thread is to check that this concept is viable despite the advice to use meanwell psus instead of atx ones, and to later allow me to work out how many peg connections it'll need.

Thanks again.

 

[fornowagain]

Meanwell psu are quire handy, I have a few of various sizes for such projects. Managed to snap up a couple of 200w 12v for a few quid each, last week in fact.

 

[PhillyDee]

Meanwell psu are quire handy, I have a few of various sizes for such projects. Managed to snap up a couple of 200w 12v for a few quid each, last week in fact.

Hmmm, do tell . Im after a 12v for a project. I was just going to butcher a PC PSU again, but I would rather have something beefier. It only needs around 6A on 1 12V line.

 

[PrincessFrosty]

The 8 pin cable is rated for 150W of power, that's twice the 6 pins power rating of 75W

With a 12v rail thats

P = I * V

or

I = P/V

150/12 = 12.5A of current standard.

I think my Quattro 850W is rated for about 18A on each 12v rail as a real world example so it can pull more if required.

 

[fornowagain]

Hmmm, do tell . Im after a 12v for a project. I was just going to butcher a PC PSU again, but I would rather have something beefier. It only needs around 6A on 1 12V line.

The odd auction comes up, often go for peanuts. Look for a something like a Meanwell SP-100, one thing to look for is models with remote relay contacts. Allows a 12v signal, from your PC for instance to start the PSU.

http://www.meanwelldirect.co.uk/ranges/Enclosed-Switching-Power-Supply/5/default.htm

The 8 pin cable is rated for 150W of power, that's twice the 6 pins power rating of 75W

I think my Quattro 850W is rated for about 18A on each 12v rail as a real world example so it can pull more if required.

The operative word there for the physical connector is 'rated' and that depends which specification and application. The rating you refer to is originally based on the ATX specification of a maximum of 240VA per connection. The PSU rail(s) itself is simply current limited, again to comply, each is under the 240VA-20A limit. The actual current limiters can be a good deal higher than the advertised values and in some cases non existent. More than a few describe rail limits, only to find on inspection its all one big single rail. Other OCPs often work in a sort of a continuous/peak type rating. For instance a rail is rated at 18A, so will hold 18A easily. But a short peak of 20A won't trip the OCP.