Sandy Bridge i5-2500k with 4-pin CPU Power Connector

[fullofzen]

In a few months, I'm planning to pick up a Asus P8P67 Pro and a i5-2500k. My existing power supply (PCP&C Silencer 470) has only a 4-pin CPU power connector. I have done several searches and many have asked whether this will do. What I haven't been able to find is someone saying "Yes, I'm using the 4-pin cpu connector with the 2500k and it's working just fine."

For its part, Asus' P8P67 manual suggests that either an 8-pin or 4-pin is acceptable, but it's just a picture showing how to do it in either scenario. There is no documentation.

To cut unwanted responses off at the path, understand that 470w is not a lot. However, since the i5-2500k is overkill for almost any game I'd want to play in the next few years I'm not looking to overclock immediately, so the Silencer 470 will last me for a while.

So the question: Is anyone currently powering a 2500k or 2600k (or any of the other Sandy Bridge i5s or i7s) with only the 4-pin CPU power connector?

 

[CtJackal]

One thing I will add is that after buying a new PSU (OCZ Fatal1ty 750W) and RMA'ing the motherboard I need far less volts for the same overclock.
Previously I needed ~1.45v to get 4.6ghz, now the same CPU is perfectly stable at 1.25v.
Whether this is a consequence of the smoother current I don't know but it's the same CPU and the same model motherboard so it would suggest that a proper 8 pin connector on a dedicated PSU rail is better than a shared single rail with a 4 pin connector when it comes to CPU voltage requirements.

 

[fullofzen]

I think it is more likely that your acknowledgely-cheap no-name power supply shorted temporarily and that's what fried your motherboard. I find it hard to believe that there would be a sudden failure of the motherboard lanes related to using a 4-pin connector. Maybe a failure over years with BSODs every so often, but a catastrophic failure? That doesn't make sense.

I'm going to say that that was probably your PSU itself causing trouble. There's no other way to explain it.

 

[RetiredChief]

jb6684 explaination was excellent and true. But there is a worst culprit than the circuit board traces and the primary reason for adding the 2nd pair of 4 wires to the ATX connector. And that is the connector itself. The contact resistance between the Male/female pins is much higher than either the wires or the circuitboard traces and therefore the highest IsqR Loss - all in the form of Heat.
Quote from CtJackal: "...When I removed the 4 pin plug there were scorch marks actually inside the socket"
I've seen a couple of other posts indicating the the plastic around the connector has melted.

This resistance also has a problem with oxidation over time (oxidation increases the resistance). Another problem deals with the quality, either the MB connector or the PSU connector which results in a poor fit and therefore higher contact resistance. Side comment: Silver is a better conductor, but never used as it is the worst for Oxidation, Copper 2nd best conductor, but also has an oxidation problem, gold plated - Gold is a 3rd rate conductor, but has 2 advantages - Slower oxidation and it is "slippery" meaning that contact pressure can be increased and still allow matting for us non 800 Lb gorillias.

Before I carry on. jaquith Has a good point - it's how the MB is laid out, Does each trace go to a dedicated VRM, or are the traces Shorted, either at the VRMs, or at the Socket - prefered. Easy to tell Just ohms check the pins at the ATX connector, if all red wires read 0 ohms to each other, they're short at one end or both.

For CPUs under 120 W (10 amps on 12V line), excluding what jaquith indicated on Phases, the 4 pin is fine, 8 pin better as IR loss at the connector is lower. The adaptor is fine also. The advantage of true 8 pin connection is that there is "Slightly" higer voltage at the VRMs, they do not have to work as hard - Very small positive, but as jaquith pointed out - ANY improvement is better.

For CPUs > 120 Watts eight pins should be used, And here I will disagree with jb6684 "EXACTLY like a "true 8 pin connector"", Not true, Yes at the motherboard it will see a "TRUE" 8 pin connection, ie the total current thru each pin will be I(total)/4. However you have added injury to insult. You still have the 4 pin connection, not on MB but at the PSU connector (injury) and you have added another connector with the added contact resistance (the Insult).
Hope I don't fall in your catagory of "(anyone who tells you different has only the tiny fractions in the 4th or 5th decimal place to back them up....)"