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12-08-2020 09:48 PM
Looking at the pinout of the power supply, primarily the middle grouping where the 3x 6 pin pci slots into, I noticed that it has available power across all 24 pins yet 18 are used. Power requirements are within spec so my question is, what is stopping me from adding another 6 pin pci power rail to the back of the case to make it 4 total leads? Does anyone have a schematic of the 1125w power supply or has anyone done this before? Seems like the entire bottom row is ground and top is solid +12v for the entire 24 pin plug. It seems like how built this into their systems for future upgradability, but never gave the option for it so it's been sitting dormant. Not trying to catch anything on fire but this could be a game changer for more pci power. Thoughts?
12-08-2020 11:04 PM
the z840 uses a power supply that is a "multirail" design, instead of the single rail power supplies now found on most consumer pc's
if you attempt to do what you suggest, you will be overloading one, perhaps more power supply rails and most likely cause major problems
the upgraded 1125 watt supply has two GPU rails, with one rail having 2x6 connectors and the other rail a 1x6 connector, you can add a 1 x2 6 pin to this rail or a 6 to x8 adapter safely as long as each rail's power draw is under the stated limit posted on the power supply and printed in the z840 service manual
12-08-2020 11:32 PM - edited 12-08-2020 11:38 PM
Understandable however I believe each rail is rated at 200w each. Since average 6 pin acceptable maximum load is 75w it should be doable especially since from the factory it has space to add another 6 pin (unlike the z820) and would still keep both of the rails under that 200w limit. A schematic of the power supply would be helpful otherwise I might be tearing one apart here in the near future.
12-08-2020 11:44 PM
again, read the supplied HP docs, the z840 1125 watt supply can power up to two 150 watt video cards if "certain" conditions are met ( or one 300 watt card) note that the 150 watt spec is the total power draw of the card, not the GPU pwr rail
12-08-2020 11:54 PM
"2x High-end graphics 150
W-225 W each (4) (5)"
225x2=450w. Pci lanes are 75w each so 300 across the gpu rails. 300/75 is 4x. According to their documentation you supplied it is theoretically possible for the 1125w power supply to handle it. Certainly can't use top end power hungry CPUs and a million peripherals otherwise, you are correct, it would overload several rails but event their site preparation guide has documentation on supporting 2x 200+ watt gpus.
12-09-2020 11:42 AM
Simply adding more wires to the PSU will not increase the available power from the PSU. You can easily split each 6-pin PCI auxilliary power connector (G1, G2 & G3) into 2x 6-pin connectors using adapter cables if required, (now giving 6x 6-pin connectors). The Z840 is rated to handle either 2x 300W, or 3x 225W GPU's as detailed in the Maintenance and Service Guide. You might also want to have a read of this thread .
12-09-2020 11:54 AM - edited 12-09-2020 12:05 PM
You are correct it won't increase capacity but it will allow a more even distribution on the second gpu rail. Pushing more than 75 watts on a single 6 pin would be ill advised from my experience . Even on the power supply it talks about the g4 connector which seems to be left out completely. I mean why do car manufacturers make fake buttons on lower model cars? For upgradeability of features for higher end or future models. I'm thinking hp had this in their upgrade path but never implemented it because of the z8 g4 rollout. Otherwise why put it there? They would have saved money on production costs by not including the g4 connector.
Also as for the thread the big mistake made there is the assumption that the z820 and z840 share a power supply. They are completely different both in external form and im going on a leap here, internally different. If someone has a dead 1125 z840 power supply they wish to donate for dissection, I will happily buy it otherwise I am going to be buying a spare one soon to confirm. I already have a z820 1125w and can confirm side by side, they are different and not interchangeable. Will be interesting to tear into both of them
12-09-2020 12:51 PM - edited 12-10-2020 09:41 AM
Each 6-pin PCI connector is rated at 18A capacity, giving a theoretical 216W handling capacity each. As the Z840 is rated to support 3x 225W GPU's then each PCI connector (G1, G2 & G3) needs to supply 150W each, (using a 6-pin to 2x 6-pin adapter cable for each GPU card - splitting each power rail (G1 to G3) into 2x 75W connections). The PSU's used in the HP Z workstations are designed well above the standard PCI power standards and will therefor comfortably power 3x 225W GPU's 24/7, 365 days a year if required - and it won't damage the PSU, (assuming you have adequate ventilation).
Admittedly, looking at the PSU label above, it does appear that the PSU has a redundant (not-connected) power rail, i.e. 12.2V-G4. However, you would still be limited to either 2x 300W or 3x 225W GPU's even if you did decide to wire an additional PCI connector to the PSU. With regards to the 'spare' power rail on the PSU, quite often the design engineers will design redundancy or safety capacity into new products. It's is at the pre-production and testing stage that the final production design is honed to meet the required specification.
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