4 ms·

> If the voltage was higher (i believe 'low volt' classification tops out at 48v) Yep, 48V through sensitive parts of the body could be unpleasant but 24V is a

by lr1970 2y ago

> If the voltage was higher (i believe 'low volt' classification tops out at 48v) Yep, 48V through sensitive parts of the body could be unpleasant but 24V is almost as safe as 12V. Why didn't they use 24V and 25A to achieve required 600W of power instead of 12V and 50A?

opencl 2y ago
Because nobody makes 24V power supplies for computers, they'd have to convince the whole industry to agree on new PSU standards.
- cesarb 2y ago
  > they'd have to convince the whole industry to agree on new PSU standards. We already have a new PSU standard, it's called ATX12VO and drops all lower voltages (5V, 3.3V), keeping only 12V. AFAIK, it's not seen wide adoption.
  - Dylan16807 2y ago
    It's not great. Dropping 5V makes power routing more complicated and needs big conversion blocks outside the PSU. I would say it makes sense if you want to cut the PSU entirely, for racks of servers fed DC, but in that case it looks like 48V wins.
    - immibis 2y ago
      There are already huge conversion blocks outside the PSU. That's why they figured there's no need to keep an extra one inside the PSU and run more wiring everywhere. Your CPU steps down 12 volts to 1 volt and a bit. So does your GPU. If you see the big bank of coils next to your CPU on your motherboard, maybe with a heatsink on top, probably on the opposite side from your RAM, that's the section where the voltage gets converted down.
      - Dylan16807 2y ago
        Those are actually at the point of use and unavoidable. I mean extra ones that convert to 5V and then send the power back out elsewhere. All those drives and USB ports still need 5V and the best place to make it is the PSU.
        immibis 2y ago
        Why is the PSU the best place to make 5 volts? In the distant past it made sense because it allowed some circuitry to be shared between all the different voltages. Now that is not a concern.
        Dylan16807 2y ago
        The motherboard is cramped, the PSU has a longer life time, and routing power from PSU to motherboard to SATA drive is a mess.
      - jrockway 2y ago
        Yup, exactly. The VRMs on my Threadripper board take up quite a bit of space.
  - masklinn 2y ago
    It's also of no use for the problem at hand, PCIe already uses 12V but that's way too low for the amount of power GPUs want.
- forza_user 2y ago
  24VDC is the most common supply for industrial electronics like PLCs, sensors etc. It is used in almost every type of industrial automation systems. 48VDC is also not uncommon for bigger power supplies, servos, etc. https://www.siemens.com/global/en/products/automation/power-supply.html?utm_source=chatgpt.com https://www.siemens.com/global/en/products/automation/power-...
armada651 2y ago
Because no PC power supply has a 24V rail and even though there's a fancy new connector you can still use an adapter to get the old-fashioned plugs. After all you don't want to limit your market to people who can afford to buy both your most expensive GPU and a new power supply. In the PC market backwards compatibility is king.
- nullifidian 2y ago
  >Because no PC power supply has a 24V rail Servers with NVIDIA H200 GPUs (Supermicro ones for example) have power supplies that have 54 volt rail, since that gpu requires it. I can easily imagine a premium ATX (non-mandatory, optional) variant that has higher voltage rail for people with powerful GPUs. Additional cost shouldn't be an issue considering top level GPUs that would need such rail cost absurd money nowadays.
  - armada651 2y ago
    A server is not a personal computer. We are talking about enthusiast GPUs here who will install these components into their existing setup whereas servers are usually sold as a unit including the power supply. > Additional cost shouldn't be an issue considering top level GPUs that would need such rail cost absurd money nowadays. Bold of you to assume that Nvidia would be willing to cut into its margin to provide an optional feature with no marketable benefit other than electrical safety.
    - ObscureScience 2y ago
      Electrical safety -> not destroying your GPU does seem like something sellable. It could probably be spinned into some performance pitch if you really want to.
    - nullifidian 2y ago
      >Nvidia would be willing to cut into its margin to provide Why would that be optional on a top of the line GPU that requires it? NVIDIA has nothing to do with it. I'm talking about defining an extended ATX standard, that covers PSUs, and it would be optional in the product lines of PSU manufacturers. The 12VHPWR connector support in PSUs is already a premium thing, they just didn't go far enough.
quickthrowman 2y ago
Cutting the ampacity in half from 50A to 25A only drops the minimum (single) conductor size from #8 to #10, also there is no 24v rail in a PSU.
johnwalkr 2y ago
A higher input voltage may eventually be used but a standard PC power supply only has 12V and lower (5V and 3.3V) available, so they'd need to use a new type of power supply or an external power supply, both of which are tough sells. On the other hand, the voltages used inside a GPU are around 1V, and a higher input voltage introduces lower efficiency in the local conversion. 12V is only really used because historically it was available with relatively high power capacity in order to supply 12V motors in disk drives and fans. If power supplies were designed from the ground-up for power-hungry CPUs and GPUs, you could make an argument for higher voltage, but you could also make an argument for lower voltage. Or for the 12V, either because it's already a good compromise value, or because it's not worth going against the inertia of existing standards. FWIW there is a new standard for power supplies and it is 12V only with no lower or higher voltage outputs.
- Neikius 2y ago
  Lower voltage would be OK, but then all of the cables and plugs would need to be redesigned. And there would still need to be for voltage switching unless we start adding a protocol and have PSU switch voltage dynamically... which is also not efficient. Since they went so far to create a new cable which wont be available on old PSU they would have easily extended that slightly and introduced an entirely new PSU class which has a new voltage also. But now they went the easy route and it failed which is even worse as they will have to redesign it now instead of it being safely done the first time.
  - 0x457 2y ago
    > Lower voltage would be OK, but then all of the cables and plugs would need to be redesigned. And there would still need to be for voltage switching unless we start adding a protocol and have PSU switch voltage dynamically... which is also not efficient. It's not like that. It's a design where PSU only provides 12V to motherboard and motherboard provides the rest. Only location of those connectors change. It's called ATX12VO. In modern PC almost nothing draws from 3v3 rail, not even RAM. I'm pretty sure nothing draws 3v3 directly from PSU at all today. 5v rail directly from PSU only used for SATA drives.
  - 2y ago

by lr1970 2y ago

opencl 2y ago

Because nobody makes 24V power supplies for computers, they'd have to convince the whole industry to agree on new PSU standards.

cesarb 2y ago
> they'd have to convince the whole industry to agree on new PSU standards. We already have a new PSU standard, it's called ATX12VO and drops all lower voltages (5V, 3.3V), keeping only 12V. AFAIK, it's not seen wide adoption.
- Dylan16807 2y ago
  It's not great. Dropping 5V makes power routing more complicated and needs big conversion blocks outside the PSU. I would say it makes sense if you want to cut the PSU entirely, for racks of servers fed DC, but in that case it looks like 48V wins.
  - immibis 2y ago
    There are already huge conversion blocks outside the PSU. That's why they figured there's no need to keep an extra one inside the PSU and run more wiring everywhere. Your CPU steps down 12 volts to 1 volt and a bit. So does your GPU. If you see the big bank of coils next to your CPU on your motherboard, maybe with a heatsink on top, probably on the opposite side from your RAM, that's the section where the voltage gets converted down.
    - Dylan16807 2y ago
      Those are actually at the point of use and unavoidable. I mean extra ones that convert to 5V and then send the power back out elsewhere. All those drives and USB ports still need 5V and the best place to make it is the PSU.
      - immibis 2y ago
        Why is the PSU the best place to make 5 volts? In the distant past it made sense because it allowed some circuitry to be shared between all the different voltages. Now that is not a concern.
        Dylan16807 2y ago
        The motherboard is cramped, the PSU has a longer life time, and routing power from PSU to motherboard to SATA drive is a mess.
    - jrockway 2y ago
      Yup, exactly. The VRMs on my Threadripper board take up quite a bit of space.
- masklinn 2y ago
  It's also of no use for the problem at hand, PCIe already uses 12V but that's way too low for the amount of power GPUs want.
forza_user 2y ago
24VDC is the most common supply for industrial electronics like PLCs, sensors etc. It is used in almost every type of industrial automation systems. 48VDC is also not uncommon for bigger power supplies, servos, etc. https://www.siemens.com/global/en/products/automation/power-supply.html?utm_source=chatgpt.com https://www.siemens.com/global/en/products/automation/power-...

armada651 2y ago

Because no PC power supply has a 24V rail and even though there's a fancy new connector you can still use an adapter to get the old-fashioned plugs. After all you don't want to limit your market to people who can afford to buy both your most expensive GPU and a new power supply. In the PC market backwards compatibility is king.

nullifidian 2y ago
>Because no PC power supply has a 24V rail Servers with NVIDIA H200 GPUs (Supermicro ones for example) have power supplies that have 54 volt rail, since that gpu requires it. I can easily imagine a premium ATX (non-mandatory, optional) variant that has higher voltage rail for people with powerful GPUs. Additional cost shouldn't be an issue considering top level GPUs that would need such rail cost absurd money nowadays.
- armada651 2y ago
  A server is not a personal computer. We are talking about enthusiast GPUs here who will install these components into their existing setup whereas servers are usually sold as a unit including the power supply. > Additional cost shouldn't be an issue considering top level GPUs that would need such rail cost absurd money nowadays. Bold of you to assume that Nvidia would be willing to cut into its margin to provide an optional feature with no marketable benefit other than electrical safety.
  - ObscureScience 2y ago
    Electrical safety -> not destroying your GPU does seem like something sellable. It could probably be spinned into some performance pitch if you really want to.
  - nullifidian 2y ago
    >Nvidia would be willing to cut into its margin to provide Why would that be optional on a top of the line GPU that requires it? NVIDIA has nothing to do with it. I'm talking about defining an extended ATX standard, that covers PSUs, and it would be optional in the product lines of PSU manufacturers. The 12VHPWR connector support in PSUs is already a premium thing, they just didn't go far enough.

quickthrowman 2y ago

Cutting the ampacity in half from 50A to 25A only drops the minimum (single) conductor size from #8 to #10, also there is no 24v rail in a PSU.

johnwalkr 2y ago

A higher input voltage may eventually be used but a standard PC power supply only has 12V and lower (5V and 3.3V) available, so they'd need to use a new type of power supply or an external power supply, both of which are tough sells. On the other hand, the voltages used inside a GPU are around 1V, and a higher input voltage introduces lower efficiency in the local conversion. 12V is only really used because historically it was available with relatively high power capacity in order to supply 12V motors in disk drives and fans. If power supplies were designed from the ground-up for power-hungry CPUs and GPUs, you could make an argument for higher voltage, but you could also make an argument for lower voltage. Or for the 12V, either because it's already a good compromise value, or because it's not worth going against the inertia of existing standards. FWIW there is a new standard for power supplies and it is 12V only with no lower or higher voltage outputs.

Neikius 2y ago
Lower voltage would be OK, but then all of the cables and plugs would need to be redesigned. And there would still need to be for voltage switching unless we start adding a protocol and have PSU switch voltage dynamically... which is also not efficient. Since they went so far to create a new cable which wont be available on old PSU they would have easily extended that slightly and introduced an entirely new PSU class which has a new voltage also. But now they went the easy route and it failed which is even worse as they will have to redesign it now instead of it being safely done the first time.
- 0x457 2y ago
  > Lower voltage would be OK, but then all of the cables and plugs would need to be redesigned. And there would still need to be for voltage switching unless we start adding a protocol and have PSU switch voltage dynamically... which is also not efficient. It's not like that. It's a design where PSU only provides 12V to motherboard and motherboard provides the rest. Only location of those connectors change. It's called ATX12VO. In modern PC almost nothing draws from 3v3 rail, not even RAM. I'm pretty sure nothing draws 3v3 directly from PSU at all today. 5v rail directly from PSU only used for SATA drives.
- 2y ago