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RocketTaco t1_iwcea74 wrote

Reply to comment by RZ_1911 in 12VHPWR adapter of the GeForce RTX 4090 - Two manufacturers, new details and exclusive information by MorgrainX

Mini-Fit is so insanely overspecified for the requirements of a PCIe unit load (which is why PSU manufacturers can offer Y-cables that use the same physical connector for two unit loads without issue) that it could have worked. The problem is they went entirely the other way and ran the Micro-Fit connector as close to the edge as they possibly could, then sold people adapters that introduce design elements not considered when Molex designed the thing. What they should have done is just shrink the PCIe 8p connector to Micro-Fit and take the opportunity to repurpose the wasted main pins from compatibility with the 6p, so that it would have an actual 4+4 power pins. You'd get a 30% reduction in size from the switch from 4.2mm to 3.0mm pitch and a 30% increase in power from using the fourth pin, for a total of 80% increase in power density and still tons of headroom for unknowns. At that point, the area occupied by the connectors would be no issue at all. But they decided to go for that 270% instead, and here we are.

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RZ_1911 t1_iwcfii5 wrote

It’s not THAT MUCH overspecified .. stable limit is somewhere 75w per rail (210w per 8p rail ) . With 100w (300w per rail ) even old 8p melted . Now imagine - they shrinked contact area for 1/2 of old 8pin connector.. and said - 100w per rail and 600w per connector- guaranteed 🤣

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RocketTaco t1_iwcid9p wrote

Mini-Fit does not melt at 100W unless significantly damaged. Molex's own spec for eight circuits onto a PCB is 10A per circuit at 16AWG (120W) for 30C temperature rise over ambient. You could run 360W on 3+3 pins before you even brush up against the safety margins which, again, are given with a third more heat since they assume all eight circuits are carrying load. Conversely, I've seen cards with two 8p connections burn one up at under 200W loading, because the receptacle was bent and didn't make proper contact.

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t0s1s t1_iwdbbik wrote

I’m reminded of my year or so of running KnC Miner Neptunes back around 2015. Similarly designed to run too close to the design specification for a 4-pin peripheral plug and socket, they caused several fires, or destroyed the miner or the PSU by melted connectors.

Even running relatively high end Corsair AX1200 supplies didn’t guarantee me a stable run, and at least one set of cables was destroyed that year.

I don’t ever want to run it like that again - the 4090 likely won’t be for me, even if it fits my case.

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