PSU wire sizing

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PSU wire sizing

Postposted on Wed Oct 16, 2013 10:31 am

I have a friend telling me the 2 power connectors on the graphics card are not required. Meaning I could use the CX430M with the one PCI-e 6-pin connector and be fine, and having two connectors on the card is for multi-rail PSUs. Anyone care to weigh in?
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Re: New Small form-factor Gaming Rig

Postposted on Wed Oct 16, 2013 10:37 am

TML wrote:I have a friend telling me the 2 power connectors on the graphics card are not required. Meaning I could use the CX430M with the one PCI-e 6-pin connector and be fine, and having two connectors on the card is for multi-rail PSUs. Anyone care to weigh in?

...what? Okay, maybe I'm not an expert on the matter, but typically when you have two connectors (double the wires, double the circuits paths), it's because you need more current that can safely be driven through a single wire or connector. Maybe you can get away with only using one, but it would be safer to connect both 6-pin connectors.
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Re: New Small form-factor Gaming Rig

Postposted on Wed Oct 16, 2013 10:57 am

To be clear, as the advising Friend here....

I didn't tell him that he shouldn't connect to both, but that it would be totally fine to use a PSU that doesn't have the two 6 pin connectors. The graphics card comes with 4pin to 6pin adapters anyways. I think the purpose of having two connectors is for two purposes:

1. To effectively increase the gauge of power cables going to the card
2. To enable connecting multiple 12v rails to the card if the PSU has limiters/multiple rails
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Re: New Small form-factor Gaming Rig

Postposted on Wed Oct 16, 2013 12:24 pm

Yes, that makes more sense.

What it really comes down to is power, as is adressed by your post. It's not that multiple connectors/wires increases the effective wire gauge, but it provides a parallel path for current to reach the GPU. Parallel currents (and therefore power) add, so your total power meets your needs. The power supply is going to have all rails grounded in the same location, but utilizing multiple rails is how you actually reach the required power/current input.

So using a 4-to-6 pin connector can work, but you'll need to make sure that whatever rail that is connected to can source the current you need. If the 4-pin you're adapting is on the same rail as the 6-pin, and that rail alone cannot supply enough current, this will not work.

If you can't check this on the PSU beforehand, you should probably stick with the Corsair for safety's sake. That way you know that you have the power you need, you know that the PSU is reliable (sometimes included PSUs are iffy), and you won't have to worry about any 4-to-6 adapters.
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Re: New Small form-factor Gaming Rig

Postposted on Wed Oct 16, 2013 1:17 pm

superjawes wrote: It's not that multiple connectors/wires increases the effective wire gauge, but it provides a parallel path for current to reach the GPU.



Same thing.
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Re: New Small form-factor Gaming Rig

Postposted on Wed Oct 16, 2013 1:20 pm

Sorry, actually it decreases the gauge, thus reducing resistance, and increasing current capacity
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Re: New Small form-factor Gaming Rig

Postposted on Wed Oct 16, 2013 1:32 pm

No...

Increasing the wire gauge decreases resistance (because electrons have more area to flow through). And it's not just a matter of resistance anyway. The power that can be supplied on a given rail is limited (for example, 10A at 12V would be 120W). Adding a second circuit essentially means connecting a second source (so another 12V, 10A, and 120W source) to meet the power requirements.

This is why you should double check whatever PSU you use. Using a 4-to-6 pin connector won't matter if the rail its coming from can't source enough current.

EDIT: Coming from EVGA's site, this is what you need.
Requirements
Minimum of a 450 Watt power supply.

(Minimum recommended power supply with +12 Volt current rating of 24 Amps.)

So if your 6-pin PCIe from your PSU can source 24 Amps, it will work. If it won't, then you'll need the 4-pin to source the additional current from a separate rail. If that 4-pin is on the same rail as the 6-pin, no dice.
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Re: New Small form-factor Gaming Rig

Postposted on Wed Oct 16, 2013 1:51 pm

superjawes wrote:No...

Increasing the wire gauge decreases resistance (because electrons have more area to flow through).



No...


Higher gauge means thinner wire, which is why I corrected myself above.

superjawes wrote:And it's not just a matter of resistance anyway.


I mentioned the possibility of multiple rails above. However, the corsair PSU mentioned above (and the one he ultimately bought), has only one 12v rail, so this does not apply. The only concern is getting enough current to the video card without putting too much through an individual cable to the point that it fails.
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New Small form-factor Gaming Rig

Postposted on Wed Oct 16, 2013 2:32 pm

Gilligan wrote:Higher gauge means thinner wire, which is why I corrected myself above.

Okay, "higher gauge" means "lower gauge number." The convention is that "higher gauge" means larger wires, not thinner. That way, when an engineer or electrician says, "We need to incrase the gauage to pass more current," we get wire with thicker diameter (therefore higher current capacity).

Source: degree in Electrical Engineering. (Hey, I didn't make up the rules!)

I mentioned the possibility of multiple rails above. However, the corsair PSU mentioned above (and the one he ultimately bought), has only one 12v rail, so this does not apply. The only concern is getting enough current to the video card without putting too much through an individual cable to the point that it fails.

Here we're on the same page.

EDIT: Speaking of bad conventions in electricity, electrons should have been the positive charge to simplify circuits!
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Re: PSU wire sizing

Postposted on Sun Nov 03, 2013 6:19 am

I have split this discussion from a system build thread and moved it out of the System Builders Anoymous forum.

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Re: PSU wire sizing

Postposted on Sun Nov 03, 2013 12:19 pm

I have a friend telling me the 2 power connectors on the graphics card are not required

it would be totally fine to use a PSU that doesn't have the two 6 pin connectors

The OP paraphrased the question incorrectly. The "not required" bit is not on the graphics card end, but on the PSU end.

Assuming the OP is not an electrician by training, why did we get into this gauge discussion in the first place? Wouldn't "as long as there is enough current/power supplied on the 12V rail(s) of the PSU, you can just use adapters and any good PSU will do" be a good enough description? Learning to read the amperage labels on the PSU is a good thing.
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