Z800 Graphics card upgrade

HP Z800 / Z820 / Z840 - Graphics cards.
I believe all three models are the same in these respects.
I have been very confused by the information on upgrading a Z800 to a more powerful graphics card, so having solved, at least the more obvious issues, I have listed my findings below to help others facing the same uncertancies.
The base Z800 did not have a video card. Video, Graphics was a user specified option.

Quick Specs - Quickspecs HP Z800 Workstation - thanks to DGroves for this link.
This document is dated 2013 so refers to the mark 3 motherboard.
My system is dated 2008 and has a mark 1 motherboard.
Do not assume your system matches any of the system descriptions as these were factory "configured" machines so could contain any number of variations.
If you wish to "mod" the workstation try to obtain one with a version 3 motherboard.
There are also a number of documents on the HP web site.
And of course there are numerous videos on YouTube.

Power supplies:
There are two power supplies - 850W and 1100W although the deliverable power varies with the mains input voltage.
The 850W equiped chassis probably have a two cable video power harness.
The 1100W equiped chassis, if they were shipped with this power unit, possibly have a three cable video power harness. There were numerous factory options on these systems so any combination is possible.

Available power:
The 16 lane edge connector can deliver 75W of power to the graphics card. Connectors 2 and 5 only.
Each of the 6 way power cables can deliver 75W of power to the graphics card.
So, theoretically, with a 1100W power unit and a three way harness you could support a 300W graphics card.
Or, with an 850W power unit and a two way harness you could support a 150W card using a single power line or 225W card using both power lines.
BUT, if you are running a two CPU system with lots of memory there will be limits on how much power is available for the graphics card. You need to study the documentation carefully.

Where are the power lines:
They are in a plain sight but unless you "know" where they are you will never guess.
They are plugged into dummy sockets on the back of the disk drive fan cage.
This short video illustrates things:
How to get free video card power plugs on the HP Z800!! - YouTube



They are 6 pin and for many video cards you will need to adapt them to mate with 2 x 6, 8 or 12 pin sockets.
HP have adapter cables to do some of this:
HP - 460621-004 for 8 pin to 1x 6 pin cable they also seem to be the same as - 460621-002, 460621-004, N1G35AA, 460621-003.



These are on sale at many web sites, BUT, although you will see the "genuine" HP items pictured, what you will be sent is a cheap oriental copy. You need one with thick wires and all 6 pins used. The diagrams shows a good copy, many are less well made. I bought a number of different cables for comparison, not all have actually been delivered. Buy the shortest adapter cable with the thickest wires. The genuine HP ones have shrink wrapped wires and a ferrite slug for RF suppression.



This diagram shows the pin connections, make sure they are all there. (see appendix)



You will need different adapters for other cards, so check the card before you buy it and sort out if/how you can connect it.

There is also a 6 pin to dual 6 pin adapter cable:
HP part no - 721858-001



If you need more than 150W you will need to connect two 6 way connectors to your graphics card. If the card only has one eight way connecter you will need a dual 6 way to single 8 way adapter. I have not found an HP part for this, but Nvidea have a picture in their official documentation:



Also these are samples from the web:



If you have a two cable system and you want to upgrade to a three cable system you will need the following cable harness.
The 3 way power harness is HP - 745061-001.
As well as the 1100w power unit.




You will need to strip the old cable harness out from the back of the power unit and thread the new one in.

If you do upgrade to this or you just want a more powerful card you NEED to make sure you have BOTH fans fitted in the disk drive fan cage. The early Z800s only shipped with one, also check you have both fans in the memory cooling system.


Motherboard edge connectors:
The HP documentation lists edge connector two as the preferred slot for a powerful video card. This is despite the fact that it interfears with the motherboard heat sink. The thinking seems to be that if you use connector 5 you will not have enough space in front of the card, fan side, for adequate air flow, cooling.
Having said that HP state you can have two high powered video cards, so you would have to use slots two and five. If you do this you need to study the power limits very carefully. (in the quick specs).
Do not use edge connector four as it can only provide 25W of power.

Choosing the graphics card:
There appears to be plenty of space in the chassis to accomodate graphics cards. But although the length is mostly not a problem the height is. You may think that there is plenty of room above the card but the snap out cover plates, which are there for optimum air flow, limit things more than is obvious. The real height limit is the top of the rear metal brackets, if the card is any heigher you may not be able to fit the covers. Also, the cables often plug into the top of the card, increasing its height. From looking at pictures on the WEB, most cards now seem to be higher than the rear bracket, presumably due to the size of the fans.
If you have a single CPU system, leaving the covers off may not be a problem, but if you have a dual CPU system this may not be so. If your card it too tall then use slot five, see my system spec below.


There is a converter unit available which enables the cable to feed in from below. Graphics cards are not standard in the way their connectors are mounted, so these are sold in pairs to enable both connector orientations to be accomodated.



My system:
My Z800 is working hapily with a Radeon RX570/8, 150W and the single 6 pin cable adapter. I have used the 8 way socket inverter so the cables feed in from below rather than above. I have fitted the graphics card in slot five as I wanted to keep the array controller card in slot two. Therefore the main air flow cover fits without a problem, but the smaller one does not. However I have cut the card retaining fingers from the cover and with a little persuasion it latches in position.

Software:
Windows 10 / 64 20H2 booted into base reolution without a problem and when I ran the AMD driver disk it rebooted into the native resolution of the monitor 1920 x 1200.

Appendix:
Credit to "Stackexchange" for the following information:
NOTE - the Z800 connectors are 75W only.

The 6 pin PCIe power connector comes in a 6.25A (75W) version and a 12.5A (150W) version. The 6.25A version only requires that two 12V power connections be present, and only two ground connections need to carry current. The 3rd middle ground connection can be used to sense that the connection is plugged in. The 12.5A version uses 3 12V power wires and 3 ground wires to carry current. An additional two groundable sense connections can be added to the side to tell the PCIe device that a 12.5A compliant power connector has been inserted. Many power supplies that are 12.5A compliant have an additional 2 pin ground connector on the side of the 6 pin connector that can be used to make it to an 8 pin connector.