[zamalek]

> Any imbalance

I watched de-Bauer's analysis this morning, and you've seemingly hit the nail on the head. Even on his test bench it looks like only two of the wires are carrying all of the power (instead of all of them, I think 4 would be nominal?) - using a thermal camera as a measuring tool. The melted specimen also has a melted wire.

Maybe 24V or 48V should be considered, and higher gauge wires - yes.

[mjevans]

It would be _lovely_ if instead of the 12V only spec we went to 48V for internal distribution. Though that would require an ecosystem shift. USB-PD 2.0~3.0 would also be better supported https://en.wikipedia.org/wiki/USB_hardware#USB_Power_Deliver...

As others no doubt mention Power (loss, Watts) = I (amsp) * V (volts (delta~change on the wire)).

dV = I*R ==> dV = I * I / R -- That is, other things being equal, amps squared is the dominant factor in how much power loss occurs over a cable. In the low voltage realms most insulators are effectively the same and there's very little change in resistance relative to the voltages involved, so it's close enough to ignore.

600W @ 12V? 50A ==> 1200 * R while at 48V ~12.5A ==> 156.25 * R

A 48V system would have only ~13% the resistive losses over the cables (more importantly, at the connections!); though offhand I've heard DC to DC converters are more efficient in the range of a 1/10th step-down. I'm unsure if ~1/25th would incur more losses there, nor how well common PC PCB processes handle 48V layers.

https://en.wikipedia.org/wiki/Low_voltage#United_States

""" In electrical power distribution, the US National Electrical Code (NEC), NFPA 70, article 725 (2005), defines low distribution system voltage (LDSV) as up to 49 V.

The NFPA standard 79 article 6.4.1.1[4] defines distribution protected extra-low voltage (PELV) as nominal voltage of 30 Vrms or 60 V DC ripple-free for dry locations, and 6 Vrms or 15 V DC in all other cases.

Standard NFPA 70E, Article 130, 2021 Edition,[5] omits energized electrical conductors and circuit parts operating at less than 50 V from its safety requirements of work involving electrical hazards when an electrically safe work condition cannot be established.

UL standard 508A, article 43 (table 43.1) defines 0 to 20 V peak / 5 A or 20.1 to 42.4 V peak / 100 VA as low-voltage limited energy (LVLE) circuits. """

The UK is similar, and the English Wikipedia article doesn't cite any other country's codes, though the International standard generally talks at the power grid distribution level.

[Denvercoder9]

> A 48V system would have only ~13% the resistive losses over the cables (more importantly, at the connections!)

It's one-sixteenth (6.25%) actually. You correctly note that resistive losses scale with the square of the current (and current goes with reciprocal voltage), so at 4 times the voltage, you have 1/4th the current and (1/4)^2 = 1/16th the resistive losses.

[myself248]

I've been beating the 48v drum for years. Any inefficiency in the 48-to-1 conversion should be mostly offset by higher efficiency in the 240-or-120-to-48 conversion, I suspect it's a wash.

Every PoE device handles 48 without issue on normal PCB processes, so I don't expect that to be a big deal either. They _also_ have a big gap for galvanic isolation but that wouldn't be necessary here.

[boznz]

POE/POE+ standard is 15-20W. 600W would mean another standard

[deelowe]

48v is basically already the standard for hyperscalers with power shelf rack designs.

[magicalhippo]

From what I can gather, one challenge with 24V and higher is that switched-mode converters, such as the buck converters used in the power stage, get a lot more inefficient when operating at high ratios.

You can see this effect in figure 6 in this[1] application note, where it's >90% efficient at ratios down to 10:2.5, but then drops to ~78% at a ratio of 10:1.

So if one goes for higher voltage perhaps 48V would be ideal, and then just accept the GPU needs a two-stage power conversion, one from 48V to 12V and the other as today.

The upside is that this would more easily allow for different ratios than today, for example 48V to 8V, then 8V to 1.2V, so that each stage has roughly the same ratio.

[1]: https://fscdn.rohm.com/en/products/databook/applinote/ic/pow... (page 14)

[crote]

> I think 4 would be nominal?

6 or 12, depending on how you count. There are 6 12V supply wires, and 6 GND return wires. All of them should be carrying roughly the same current - just with the GND wires in the opposite direction from the 12V ones.