5 ms·

Why can’t they just use a cable+socket similar to PSU - wall socket? It’s not even multiple-kilowatts range.

by wruza 2y ago

vvv5 2y ago
That connector (C13) is rated for 15 amps. That's 180W at 12V.
- wruza 2y ago
  So heat depends on current, not on power. My research: https://www.reddit.com/r/ElectricalEngineering/comments/15xfet7/soo_what_actually_generates_heat/ https://www.reddit.com/r/ElectricalEngineering/comments/15xf...
  - cwillu 2y ago
    And the card requires up to 600 watts, which is 50 amps if the supply is 12 volts.
  - hgomersall 2y ago
    No it depends on power, but the power dissipated by the cable, not the power through the cable. The power dissipated is i^2 * r, where r is the resistance of the cable and i, crucially, is the current through the cable which depends on the power it's supplying (which with a resistive load, in this case, is i * 12v).
    - gorjusborg 2y ago
      Yes, but it seems the connectors, not the entire cable are too high resistance. Using a larger diameter wire would drop resistance in the cable, but if it has to go through the same connector, it will likely still get hot. Also, NVDA might be telling the truth about poorly seated connectors, that could raise resistance and heat significantly. That could also be handwaving away a business decision to move forward with a design with too little margin.
- dcrazy 2y ago
  I’m not sure what you’re trying to suggest here… the PSU is also connected to the wall with a C13 connector, and is able to supply 600W at 12VDC to the card.
  - vvv5 2y ago
    Yes, but the voltage on the wall side of the psu is not 12V it's 120-240V. And 600W at 120V requires only 5A of current. It's easier to handle more power at higher voltages because heat produced depends on current and not on voltage. If you take that puny C13 connector and move it to the 12V side with its 50A it would just melt.
hgomersall 2y ago
It's 12V, which means the currents are very high (like >40A). It feels like perhaps they need higher voltage power supplies.
- vvv5 2y ago
  I think the problem with this is that chips can only use a relatively low voltage around 1-1.5 volts. So if you supply 48 volts to the card it still has to be stepped down and this means more components and heat dissipation on the card. We are basically arriving at the idea of graphic cards having their own integrated PSUs, but this doesn't fit well with the current physical design of computers.
  - CharlieDigital 2y ago
    I feel like it could work with an external power brick and the card exposing a dedicated external port.
    - Dylan16807 2y ago
      For what purpose? That gives you similar cabling problems to internal connections, but now that cable is far less protected.
      - CharlieDigital 2y ago
        It would be a different connector and it moves some mass and heat outside of the case.
        Dylan16807 2y ago
        If you want a different connector then just use a different connector. Moving 5% of the mass and 1% of the heat outside the case is a bad thing. One of the main purposes of the case is to be one big hunk of mass.
  - deleted 2y ago
    [deleted]
ch_123 2y ago
I'm aware of at least one card which did this, which was a custom OEM design (specifically from Asus) which put two Geforce 7000-series GPUs on a single card: https://pcper.com/2005/10/asus-n7800gt-dual-review-7800-sli-on-a-single-card/2/ https://pcper.com/2005/10/asus-n7800gt-dual-review-7800-sli-... Thankfully, I've never seen something like it since then.
- voxadam 2y ago
  3dfx did it even earlier with the Voodoo 5 6000 all the way back in 2000.[1][2] [1] https://www.extremetech.com/gaming/325466-i-wrote-the-first-full-review-of-the-voodoo-5-6000-3dfx-isnt-coming-back https://www.extremetech.com/gaming/325466-i-wrote-the-first-... [2] https://www.techpowerup.com/gpu-specs/voodoo5-6000.c3536 https://www.techpowerup.com/gpu-specs/voodoo5-6000.c3536

Why can’t they just use a cable+socket similar to PSU - wall socket? It’s not even multiple-kilowatts range.

by wruza 2y ago

Why can’t they just use a cable+socket similar to PSU - wall socket? It’s not even multiple-kilowatts range.

vvv5 2y ago

That connector (C13) is rated for 15 amps. That's 180W at 12V.

wruza 2y ago
So heat depends on current, not on power. My research: https://www.reddit.com/r/ElectricalEngineering/comments/15xfet7/soo_what_actually_generates_heat/ https://www.reddit.com/r/ElectricalEngineering/comments/15xf...
- cwillu 2y ago
  And the card requires up to 600 watts, which is 50 amps if the supply is 12 volts.
- hgomersall 2y ago
  No it depends on power, but the power dissipated by the cable, not the power through the cable. The power dissipated is i^2 * r, where r is the resistance of the cable and i, crucially, is the current through the cable which depends on the power it's supplying (which with a resistive load, in this case, is i * 12v).
  - gorjusborg 2y ago
    Yes, but it seems the connectors, not the entire cable are too high resistance. Using a larger diameter wire would drop resistance in the cable, but if it has to go through the same connector, it will likely still get hot. Also, NVDA might be telling the truth about poorly seated connectors, that could raise resistance and heat significantly. That could also be handwaving away a business decision to move forward with a design with too little margin.
dcrazy 2y ago
I’m not sure what you’re trying to suggest here… the PSU is also connected to the wall with a C13 connector, and is able to supply 600W at 12VDC to the card.
- vvv5 2y ago
  Yes, but the voltage on the wall side of the psu is not 12V it's 120-240V. And 600W at 120V requires only 5A of current. It's easier to handle more power at higher voltages because heat produced depends on current and not on voltage. If you take that puny C13 connector and move it to the 12V side with its 50A it would just melt.

hgomersall 2y ago

It's 12V, which means the currents are very high (like >40A). It feels like perhaps they need higher voltage power supplies.

vvv5 2y ago
I think the problem with this is that chips can only use a relatively low voltage around 1-1.5 volts. So if you supply 48 volts to the card it still has to be stepped down and this means more components and heat dissipation on the card. We are basically arriving at the idea of graphic cards having their own integrated PSUs, but this doesn't fit well with the current physical design of computers.
- CharlieDigital 2y ago
  I feel like it could work with an external power brick and the card exposing a dedicated external port.
  - Dylan16807 2y ago
    For what purpose? That gives you similar cabling problems to internal connections, but now that cable is far less protected.
    - CharlieDigital 2y ago
      It would be a different connector and it moves some mass and heat outside of the case.
      - Dylan16807 2y ago
        If you want a different connector then just use a different connector. Moving 5% of the mass and 1% of the heat outside the case is a bad thing. One of the main purposes of the case is to be one big hunk of mass.
- deleted 2y ago
  [deleted]

ch_123 2y ago

I'm aware of at least one card which did this, which was a custom OEM design (specifically from Asus) which put two Geforce 7000-series GPUs on a single card: https://pcper.com/2005/10/asus-n7800gt-dual-review-7800-sli-on-a-single-card/2/ https://pcper.com/2005/10/asus-n7800gt-dual-review-7800-sli-... Thankfully, I've never seen something like it since then.

voxadam 2y ago
3dfx did it even earlier with the Voodoo 5 6000 all the way back in 2000.[1][2] [1] https://www.extremetech.com/gaming/325466-i-wrote-the-first-full-review-of-the-voodoo-5-6000-3dfx-isnt-coming-back https://www.extremetech.com/gaming/325466-i-wrote-the-first-... [2] https://www.techpowerup.com/gpu-specs/voodoo5-6000.c3536 https://www.techpowerup.com/gpu-specs/voodoo5-6000.c3536