I agree caution when expanding but I pulled this from HP website. As long as he is using the PCI x16, he should be ok.


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This shows that each of the 2 PCI x16 slots has a max rating of 75 W each.

The next lines says the following "The maximum graphics configuration with an 475W power supply can include two 75-watt cards (one in slot two, one in slot four), or one 150-watt card in slot two or slot four."

Batter, thank you, do you have any links to info on an adapter?

These are not HP products but Chines knock offs form souses that come and go. I would not use one so I don't want to point you to something that may fry your machine.

It can be done but I wouldn't risk a 780ti, that is what old parts are for.

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The cards listed in the Z400 PDF include AMD cards that are rated at <75W. The PCIe Standard calls for 75 watts available to each slot. I personally have a host with a GTS250, that's rated at 150 watts with one 75w aux plug, connected to a PCIe 1x slot. I also have an 8800GT, rated at 125w, in the 16x slot. The Q9400 is rated at 105w, and all of them are running off a 500w, 6 year old, PC Power & Cooling power supply. Been working together for months 24/7.
I don't think you will have any trouble running 2 ~65 watt cards with a 475w power supply.
HP Z400 Workstation PDF
2 AMD FirePro V5900 2GB Graphics...

It´s not just about the PSU capacity, some other point is important.

Not forget the ohm law, 150W @ 12V = 12.5A!!! To much for the small contacts on the 20/24 Pin power connector or 1/2 of that in the PCIe even smaller connectors.

That´s could be OK for gaming who actualy not use the GPU at full 100% of the time, but for crunching, who actualy could do that, I have my doubts.

Please note, i´m not say not works, it´s work, but the question is for how long, high current even under small resistences produces a lot of heat, that heat will sooner or latter destroy the contacts on the PCIe or the Power Connector.

I have serious bad experiences with that, and there are a lot of other users who have too just see the forums, so avaid to use more than one GPU powered directly from the PCIe. You could discover i´m right when you compleately loose the MB due a melted connector.

Thats is the reason why for multiple GPU´s it´s allways better to drive all the power from the direct high current 6/8 Pin conectors.

Of course if he choose to use only one 75W GPU his PSU will easely handle and he could totaly ignore my post.

my 0.02Cents

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The PCIe STANDARD calls for 75 watts to be available to the Slot.

It's the STANDARD

All PCIe motherboards are designed to pass 75 watts to the slot. My 6 year old Mac has 4 Slots and it was Advertised to be able to run Four 75 watt video cards at once...in 2008!
If you had a problem trying to pull 75 watts through a PCIe slot, then you had a faulty board that didn't meet PCIe STANDARDS.
Why do you think they make 150 watt Video Cards with ONE 75 watt Plug and Crossfire/SLI connections?

I will not argue with that, Maybe some reading will help...

http://www.tomshardware.com/reviews/power-supply-specifications-atx-reference,3061-7.html

This means the total power-handling capacity of this connector is only 251 watts if standard terminals are being used, which is lower than most systems need today. Unfortunately, drawing more power than this maximum rating through the connector causes it to overheat.

Observation: 251W is the total for the GPU, CPU, memory, chipset, MB etc...

Because the ambient temperature inside a PC can run 40°C (104°F) or higher, running power connectors at maximum ratings can result in extremely high temperatures in the connectors.

Remember i´m not saying not work, it works, but is not safe to use something at 100% of it´s capacity.

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True but HP says the Max is 75 W per PCI x 16.... The Nvidia GTX 750 Ti are only drawing 60 W. They aren't close to the max, so he should be fine with 2 of them. True he could go for a lower class of GPUs but we are looking at best bang for the buck. Low power, low cost, no need to change out the PSU or pins. I still think he should stick with the GTX. My 2 cents..

Plugs and voltage are dangerous things to play with. I had a power supply with enough voltage but not enough plugs for my GPUs. I bought a splitter for one of the 8 pin PCIe plugs. It worked fine for a month or so then I got power warnings. The eBay splinter I bought was partially melted. Fortunately it didn't melt where it plunged in to the 690. That is why I caution the OP to proceed with caution. Voltage can cook a machine in the blink of an eye.

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True but HP says the Max is 75 W per PCI x 16....

Yes but not all at the same time... that´s what i´m trying to explain. Look the Batter Up previous post, for the record, is not the voltage who cook the component, it´s the heat generated by the current when passes thru the small connector resistance the old law: P = R*I^2 still applies.

The Nvidia GTX 750 Ti are only drawing 60 W. They aren't close to the max, so he should be fine with 2 of them. True he could go for a lower class of GPUs but we are looking at best bang for the buck. Low power, low cost, no need to change out the PSU or pins. I still think he should stick with the GTX. My 2 cents..

60W per card it´s diferent, working with up to 80% of maximum capacity is relatively safe.

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I will not argue with that, Maybe some reading will help...

http://www.tomshardware.com/reviews/power-supply-specifications-atx-reference,3061-7.html

This means the total power-handling capacity of this connector is only 251 watts if standard terminals are being used, which is lower than most systems need today. Unfortunately, drawing more power than this maximum rating through the connector causes it to overheat.

Observation: 251W it the total for the GPU, CPU, memory, chipset, MB etc...

Because the ambient temperature inside a PC can run 40°C (104°F) or higher, running power connectors at maximum ratings can result in extremely high temperatures in the connectors.

Remember i´m not saying not work, it works, but is not safe to use something at 100% of it´s capacity.

So...your saying that the people that developed the PCIe STANDARD didn't know what they were doing? The people that have been manufacturing 75 watt capable PCIe standardized motherboards since...forever, have been manufacturing defective products? Pleeze.

All PCIe complaint Slots are capable of delivering up to 75 watts. It's the PCIe Standard, ALL PC PCIe MOTHERBOARDS ARE DESIGNED THIS WAY. What on Earth are you supposed to do with all those Video cards that don't have a power plug?

This is not a HP thing, it's the ENTIRE Industry. Please do some research before passing bad information. I can't believe you are telling people their video card shouldn't draw up to 75 watts through the PCIe slots when they were designed to do exactly that. Someone trying to push too much power through the wrong size wire has nothing to do with the Industry STANDARD of delivering 75 watts to a PCIe slot.

Maybe is my bad english, i´m not saying ONE 75W GPU will not work on a PCIe standard slot, or you must not use it, please don´t subestimate me, what i said, more than one, 2 3 or more GPU´s each one on his 75W PCIe capacity slot will overload the total capacity of the 12V rail on the 20/24 power connector, an this connector could (please note could not sure will) melt and if that happening that could destroy the MB.

I see a lot of 20/24 pin connector melted and a lot of MB ruined because exactly that, the sum of the current exceded the connector capacity not the current itself on each component (not just because the GPU´s itself, anything who is powered by the 12V on the MB, including the CPU Fans for example, all counts). I´m sure you know that.

I´m leaving, my only ideia was to share some experience and explain how to safely choose the right GPU in order to build a long lasting cruncher, something who could work for years without problems. If you think i´m wrong, please forgive me.

BTW I have few hosts with 650, 8800, 9600, etc. GPU´s, just don´t use them for crunching.

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People that don't follow the STANDARDS are bound to Destroy equipment, just as those that try to push too much power through the wrong connections/wires. I don't recall Apple having to replace motherboards because people ran FOUR 75 watt PCIe video cards in their products just as Advertised. I doubt HP would sell TWO 75 watt video cards in their Z400 if there was any way it would damage their product. That's what STANDARDS are for, to allow companies to market products they can rely on. Likewise, if you aren't intelligent enough to follow the STANDARDS, maybe you should buy from someone who is. Do you really think you are better suited to design a produce than the rest of the industry? To tell someone that respected companies in the industry don't know what they are talking about?

I'll go with HP on this one. There isn't any problem running two 75 watt cards on a motherboard in a machine classified as a Workstation. Or even FOUR 75 watt cards in the exact Workstation I own.

Which is 1 good thing about my ASRock motherboard as it has a molex power connection near the PCI-e slots to provide more power to them when multiple cards are installed.

Cheers.

Thanks Guy you explain what i try to said with better words. Hope others understand that too, drain to much current on our little 12V conectors and yellow wires is allways a possible source of headaches.

FYI Humidity, NO, On the contrary i live at about 1000 meters so the air is relatively dry, far from the Brazilian tropical raining forrest.

@Wiggo i allready work with one MB with that extra connector in the past, that´s was an interesting technical solution before the 6/8 pin VGA connector. This connector adds an extra 12V line to power the PCIe devices, exactly to avoid the 12V power connector overload. The only problem is the 3 pin molex conector they use can´t handle to much current too but helps a lot when you need to power more 12V devices directly from the PCIe slot.

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Motherboard PCIE connector:

75 watts supplied from the motherboard to each PCIE circuit card is a lot.

There are only 5 pins assigned for +12

http://en.wikipedia.org/wiki/PCI_Express

Pin 1 (side A)
Pin 2 (side A and B)
Pin 3 (side A and B)

(Plenty of ground pins available for return)

75 watts is 6.25 amps; which means each pin must pass 1.25 amps.

Pins look like this:

http://www.tomshardware.com/gallery/pciexpressx16,0101-98892-0-14-15-1-jpg-.html

Those of us with experience see this is pushing the limits.

Motherboard P1 connector:

Only two pins (#10 and #11) for 12 volts from the power supply to the motherboard (yellow).

As Juan pointed out, 2 X 75 Watts is 12.5 Amps (plus what ever else is drawing 12 volts on the motherboard.)

Those of us with experience know this is pushing the limits through those two *little* yellow wires. (22 gauge maybe?)

The most important thing is the connections themselves--where bare metal touches other bare metal to make an electrical connection. Good, clean, firm connections, and you probably won't have any problem. Any kind of contaminant (such as oils from your fingers) will cause corrosion sooner or later depending on several other environmental factors. (Edit: Juan, do you normally have high humidity?) Corrosion causes resistance. Resistance causes voltage drop. Voltage drop causes heat. Heat causes more corrosion. And the cycle continues until something melts.

What's the warranty period? Maybe one year? My guess is that it will melt at 13 months.

Kind of like running your car engine just below the red line on the tachometer. It's the standard, but would you recommend it?

Are you by chance a member of the PCI Special Interest Group? Sorry, I'm going to have to go with that group for advisement. Considering the ENTIRE PC Industry uses the same Standards and Untold Millions of Computers work just fine following the PCIe standards, I'm finding it difficult for people to claim that something that works in Millions of Computers is flawed. Especially when the number of people claiming the 'flaw' is so small. Do you have any idea of how many Millions of computers are running at least Two Video cards that are drawing 75 watts from their PCIe slot? I know I have three. ALL modern Video cards are designed to draw the first 75 watts from the PCIe slot.

One of you should call HP, Apple, Dell, etc and tell them they don't know how to build computers. That should be fun...

Hi Folks, thanks for all the discussion. I decided to install a geforce gtx 750 ti till I sort out the power supply issue.

Robert

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http://allprojectstats.com/ts593244b0a.png

Yup, no matter what your opinion of PCI and power, that should just work. :)


Ian

A perfect choice if you don´t want to change the PSU, your system could easely handle it without any power supply issues and you could even think to add one more in the future without the need to mess with anything else. Congrats.

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Hi all, click on my name link to see new pc!!!!!

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http://allprojectstats.com/ts593244b0a.png