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11-05-2021 02:58 AM
I do believe you already have what you need if you get the right adapters from HP... time to do some homework on their part numbers. This will get you started:
11-05-2021 12:59 PM
I don't, because I get 3 Pci-E plugs, G1, G2, and G3, which can be adapted to 8 pins with the HP adapter, but I need 1 more, since both cards take two 8 pins each. I can either do some kind of SATA adapter, but I don't trust those as much as if I could use the CPU1 12A plug instead. So my question is can I adapt the CPU1 plug into 8 pins.
11-05-2021 03:56 PM - edited 11-05-2021 03:58 PM
the z820 1125W power supply CAN run three 8 (or 4) pin GPU connectors off of the three 6 pin GPU connectors using six to 8 pin adapters as long as you don't exceed the power supplies TOTAL AVAILABLE OUTPUT ON THE GPU RAIL
this is what HP does for "CTO" (custom To Order) configurations
you do however need to use the CORRECT TWO GPU CONNECTORS if you look at the power supply label you will note two of the GPU connectors come off of one line and the third GPU connector is on a separate power rail
you want to spread the load across both GPU power rails so you need to connect a 8 pin adapter to the single GPU line and the other 8 pin adapter to one of the two 6 pin GPU connectors
as SDH pointed out, time for you to do some reading, or you do have the right to hack the system and perhaps cause serious damage/problems
here's another previous reply from SDH on this subject
The thing to know is that the HP PCIe supplemental power cables coming from the HP power supplies provide much more wattage than a "ATX-standard" cable. The ATX standard cable is 75W max. The HP cable is rated for its amperage times voltage (18A x 12V = 216 Watts). The amperage for each HP PCIe supplemental power supply is listed on the HP power supply label (usually has a G1/G2/G3 in its code). For years each of these HP cables has been rated for up to18A.
There are some very cheaply made 6-pin to 8-pin adapters out in the market. Some have only a fraction of their sockets populated with wires. Some have tiny wires rather than HP-spec thicker wires. At 25-30 bucks I'd always go with the HP adapter and know that my video card could pull a full 216W through that adapter. Please also note that the card slot itself provides 75W up to the card. Thus, your card will be getting access to a full 291W to play with from the slot plus the cable, but only if you have a properly engineered adapter. I'm not saying only the HP adapter can pull this off, but I am saying that many others can not (and how do you know the good from the bad?).
personally, i would go with the HP approved method......................................
11-05-2021 08:15 PM
How would I get four 8pin connectors from the three PCIE connectors? (G1, G2, and G3). I read that G1 and G2 were on the same rail and G3 was on another rail, but I don't know how I could read that information off the power supply label. All three come from the middle connector on the power supply.
If I put the approved HP 6 to 8 pin adapters on those three, I still need one more, because I have two GPUs that take two 8 pin power cables EACH. So I need four total, which is why I was wondering if I could adapt the CPU1 power cable to an additional 8pin power cable, as it is also 12V at 18 amps I think. I also read somewhere there are three rails total on that power supply, so if possible I would like to get the other rail involved.
Thank you guys for your help.
11-05-2021 08:53 PM - edited 11-05-2021 09:56 PM
You're now talking about two cards each needing two 8-pin PCIe supplemental power inputs. Exactly what are card 1 and card 2, and their specs as far as total wattage for each?
Depending on what you have I could imagine a higher wattage card 1 in the upper (primary) PCIe x16 video card slot, and a somewhat lower wattage card in the lower (secondary) PCIe x16 slot. Don't forget that each slot provides 75W up to the card, and then each of the supplementary PCIe cables in the HP workstations provides the previously stated 216W power (well above the ATX standard of 75W for each PCIe supplemental power cable).
Next, buy one HP brand 6-pin to dual 6-pin adapter. Plus, you also buy two HP brand 6-pin to 8-pin adapters. Then, from the G3 cable end you combine these and end up driving two 8-pin high quality plugs into that second card.
So, what truly is card 2's wattage needs? 216W + 75W = 291W total... that is what you have to play with for card 2. What kind of a monster are you creating, Herr Doktor?
11-05-2021 11:04 PM
I defer to DGroves on whether the conservative headroom HP engineers into its highest end Z820 power supplies gives you enough to not worry. Remember that the needs of the card are lower when the work level is less, and my guess is that you would be fine for the plan on card 2.
11-06-2021 11:06 AM
trying to run two 3080's in a z820 is not recommended because it exceeds the HP recommended wattage draw on the GPU rail
the z820 power supply uses separate power rails for each voltage and each rail has a max wattage limit
this means that if you have a 100 watt limit on the gpu rail you can not use the free watts on another rail rail for the gpu rail as each rail is a separate power connection unto itself
most pc power supplies made nowadays are single rail designs, which means that all power connectors share the wattage from a single rail and only the combined total wattage matters
there are benefits to each power supply design, however the advances to current power supply micro controllers has negated most of the benefits a multi rail supply offers which is why you no longer see them in consumer systems and low end workstations
second the z820 is not a ideal platform for these cards as the available cpu's are not able to feed data to the GPU at the rate the GPU wants (in other words the cpu is bottlenecking the systems potential performance)
last, how do you get four 8 pin connectors from three 6 pin? simple you use a six pin to dual 8 pin adapter
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