Just double checking some facts on PSUs

[krnmastersgt]

So about to swap in my EVGA 650W PSU into my main rig and was unsure of how the rails and my 780 were going to work together. From what I understand (from the sticky in this section) it's likely all off 1 trace anyways BUT the PSU does have the 12v split over multiple listed rails with a 20A max on each.

The GTX 780 however has a listed max draw of 250W, now my whole system is about to go under water and I do plan on OCing it as much as I can, and since a single rail in theory would only supply 240W of power before hitting its OAP and shutting off do I need to run multiple power connectors off the PSU to the video card? Reason I'm checking is I have an 8 to dual 8 pin connector cable but not sure if that coming off a single "rail" would just trip the OAP when the card is maxed out (not likely I think outside of benchmarking but just checking).

One other question I had is related to the resistances on some of the wires on my 24 pin connector. As it stands most of the cables seem to be 18 awg wires, but there are a few that seem to be a higher guage though mostly grounds I believe. Would it be dangerous or affect the PSU at all if I were to replace the wires themselves with the same 18 awg that the other wires are?

 

[Meghan54]

So about to swap in my EVGA 650W PSU into my main rig...

If you're replacing the Antec HCG-850 in your sig with that EVGA 650, I must ask why you're replacing a quite good power supply with one that's not so good (worse voltage regulation, worse ripple/noise suppression, worse constuction quality)? Just curious.....

 

[Deders]

Those thicker gauge wires are there for a reason, you'll notice they are for 12v and are needed to supply 75W of power to each of your PCIe slots. So definitely don't change those.

Your GPU will draw up to 75W from the PCIe slot, and (as you probably know) up to 75W from a 6-pin and up to 150W from an 8-pin.

Which 780 model are you using that has 2 8-pin sockets? Mine has 1 6-pin and 1 8-pin.

Probably worth checking that 16AWG will handle 250W@12v or 20.83A or your wires might get too hot.

I estimated this from worst case scenario if you were to custom flash your bios to allow for higher than the 250W TDP, if for instance it allowed you to supply 300W through the connectors and 50W of that was supplied through the PCie slot.

For piece of minds sake I'd rather have each connector coming from a different wire from the PSU.

 

[krnmastersgt]

If you're replacing the Antec HCG-850 in your sig with that EVGA 650, I must ask why you're replacing a quite good power supply with one that's not so good (worse voltage regulation, worse ripple/noise suppression, worse constuction quality)? Just curious.....

@Meghan Actually the original unit was a Corsair AX850 however I'm having a lot of issues with the fan and it's temp sensor as it never seems to spin regardless of the load or temperature, but the fan seems functional so I'm not sure. Was producing a strange smell reminiscent of some other PSU's I've had melt so rather wary to use that.

As for the Antec, it's been a great unit for me for a while but it's always been used as a test/back up PSU for me and will still keep it as a back up.

As for why the EVGA, still deciding if I want to utilize it for this build but it ended up being my cable sleeving practice unit as it was the cheapest fully modular unit I could find (nabbed it for ~$40) and the slightly higher efficiency seemed promising at the time. Did read about the rather poor voltage regulation after the fact which is the only reason I didn't just swap the unit in immediately. Also the Antec's fan seems rather loud compared to the other PSU's I've been using in some other work/builds.

That being said this is just a curiosity as I might end up grabbing a an 850W EVGA SuperNova (very well reviewed and quite excellent price, also gives me headroom for likely SLI in near future) . Might end up swapping in the NEX650G for some pictures as a demo, and then just retire it immediately to my parts closet for another build. I like having spare PSU's on hand for quick builds or tests anyways.

@Deders I wasn't going to change the thicker wires as they make up most of the cables, but was wondering if there was any harm in "beefing up" the thinner wires, I figured the resistance might be an issue but not sure it'd matter a whole lot on what I believe are grounds. Need to check a diagram later to be sure.

My EVGA 780 SC has a 6+8, but the cable that the NEX has is a 8 to 2 x 6+2s, should have clarified I guess. Was just curious if it was possible/okay to run the single cable and reduce an extra cable being run but will just run 2 of the cables instead I suppose.

 

[Deders]

Ahh, I see the confusion. 16AWG is actually thicker than 18AWG, so replacing wires with 18AWG would either mean 18AWG to 18AWG (same), or downgrading from 16AWG to 18AWG.

I can't see any benefit from upgrading the 18AWG wires to 16AWG as the currents that run through them are too low.

If you look at this chart for guidance, it's the Maximum amps for chassis wiring column you should be interested in.

22A x 12v = 264W for 16AWG, might be worth double checking to see if EVGA have used this thickness or if it is thicker.

It should be possible to run a 6 and 8-pin adapter from one wire, so long as you stick to the stock bios when overclocking. Bear in mind that even though anything up to 75W can be drawn from the PCIe slot (it varies greatly between graphics card designs, I saw a chart where a french website had tested lots of cards with an adapter that measured 12v power drawn from the slot when running Furmark. Some were as low as 22W and notably 8800GT's actually drew 88W. These were the only cards at the time that were out of spec, and the results were pre Fermi)

If you were to flash the bios to one that allowed for a higher power draw (I think the Skynet ones range from allowing 330W to 500W) then it would probably be safer to have them on separate wires.

If you did go with the adapter from one wire, then personally I'd still want to feel how warm it can get under load for peace of mind.