Question Can I power up ATX 24pins motherboard with 3 pieces of 8pin cables instead?

yazooda

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Nov 19, 2014
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Guys I bought a 1400w PSU that only has 6pin type slots from it, and it came with 16 cables of 6pin to 8pin. Unfortunately I forgot that I need 24pin cable for the motherboard. Instead can I use 3 cables of 8pin which = 24pin? Telling that every cable is coming from a separated slot of 6pin from the psu.



 

DSzymborski

Polypheme
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Just to eliminate any confusion, please try not to call cables "6 pin to 8 pin" when you're talking about 6 pins on the modular PSU itself. These pins are not standard so it can be a bit confusing, which is a problem as the exact right answers are very important here! PCIE cable are either 6-pin cables or 6+2 pin or sometimes 8-pin cables, depending on what is on the end that connect to the component. The number of pins on the modular power supply connectors themself are never important as identification.

You have to use the proper motherboard cable that came with the PSU. PCIE cables do not have the same pinout at the ends as CPU ones. Plugging in a CPU for a cable intended to power a PCIE slot would very likely result in you no longer owning a CPU. Or worse.
 

yazooda

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Nov 19, 2014
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Just to eliminate any confusion, please try not to call cables "6 pin to 8 pin" when you're talking about 6 pins on the modular PSU itself. These pins are not standard so it can be a bit confusing, which is a problem as the exact right answers are very important here! PCIE cable are either 6-pin cables or 6+2 pin or sometimes 8-pin cables, depending on what is on the end that connect to the component. The number of pins on the modular power supply connectors themself are never important as identification.

You have to use the proper motherboard cable that came with the PSU. PCIE cables do not have the same pinout at the ends as CPU ones. Plugging in a CPU for a cable intended to power a PCIE slot would very likely result in you no longer owning a CPU. Or worse.
Although that made me sad that I have to wait more time to get 24pin cable, but still happy to hear these warnings before I would burn something!
 

Karadjgne

Titan
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Pcie cables = 12v + ground.
EPS cables = ground + 12v.
20+4 cable = 3.3v, 5v+, 5vvsb, -12v, 12v, power on, grounds etc.

So no, you cannot just use adapters or other cables to supply the 20+4 mains for the motherboard, doesn't work that way. The psu could have 4pin outlets or 12pin outlets, that doesn't matter, that's just a physical connection of the cable to psu. What matters is the motherboard end of the cables as those need to match up power to power, ground to ground etc. Putting psu ground to motherboard 12v or vice-versa when more than one power wire goes to the same plane = dead short = non functional psu if it has good protections, or blown up motherboard/psu/gpus/cpu/ram if it does not.
 
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DSzymborski

Polypheme
Moderator
Although that made me sad that I have to wait more time to get 24pin cable, but still happy to hear these warnings before I would burn something!
What PSU doesn't come with its cables? Also note that when I say that modular cables are not universal I really mean it; any cables you get that don't come with a PSU have to be specifically advertised as working with the exact PSU in question. Pinouts are not identical from manufacturer to manufacturer. The wrong cable can result in magic smoke as well. Sorry to sound like a hectoring schoolmaster, but I really don't want you to damage your equipment!
 

yazooda

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What PSU doesn't come with its cables? Also note that when I say that modular cables are not universal I really mean it; any cables you get that don't come with a PSU have to be specifically advertised as working with the exact PSU in question. Pinouts are not identical from manufacturer to manufacturer. The wrong cable can result in magic smoke as well. Sorry to sound like a hectoring schoolmaster, but I really don't want you to damage your equipment!
Yes, you really saved the day actually. Now I understand something new about cables. Thanks.
 

yazooda

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Nov 19, 2014
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Pcie cables = 12v + ground.
EPS cables = ground + 12v.
20+4 cable = 3.3v, 5v+, 5vvsb, -12v, 12v, power on, grounds etc.

So no, you cannot just use adapters or other cables to supply the 20+4 mains for the motherboard, doesn't work that way. The psu could have 4pin outlets or 12pin outlets, that doesn't matter, that's just a physical connection of the cable to psu. What matters is the motherboard end of the cables as those need to match up power to power, ground to ground etc. Putting psu ground to motherboard 12v or vice-versa when more than one power wire goes to the same plane = dead short = non functional psu if it has good protections, or blown up motherboard/psu/gpus/cpu/ram if it does not.
Informative, thanks! Although I just heard about what is called PicoPSU and I think I read that it can solve my problems.
 

Karadjgne

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Pico psu is TINY. It's meant to power low power objects like a laptop or tiny box. It's most definitely not designed to run a fully powered pc.

It looks like you are trying to build a mining rig with that psu, which I'm going to assume was used since it did not come with a mains cable. Every brand new psu that I've ever seen comes with the necessary cables. Eps, mains, molex/Sata at a minimum.
 

madmatt30

Titan
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What PSU doesn't come with its cables? Also note that when I say that modular cables are not universal I really mean it; any cables you get that don't come with a PSU have to be specifically advertised as working with the exact PSU in question. Pinouts are not identical from manufacturer to manufacturer. The wrong cable can result in magic smoke as well. Sorry to sound like a hectoring schoolmaster, but I really don't want you to damage your equipment!
There are mining rig psu's out there that are 12v only and only have pci express power cables, dedicated mining rigs require an independent supply for the board etc.
 

Karadjgne

Titan
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I've never liked split systems. Because they aren't split. Ground planes are open access, pcie power is open access, you are literally mixing power sources with 2 seperate phases. That's OK with a single source, it all goes back where it came from and draw is whatever it is, but adding a second psu means it's power is also going back to ground through the first.

Even the 12v only psus are single source, the motherboard to use those with has its own 3.3v and 5v rails built in, so effectively a single source, you get only the power that psu is capable of. I'd hate to think of what would happen to a standard 450w psu that has possibly the entire grounded load put back through it.
 

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