6 gpu add2psu configuration

[boondock66]

hi, im in the process of building my 6 x sapphire r9 280x vapor-x rig

currently i have 2 x corsair ax 860w psu's so 1720w total using an add2psu connector
 
do you think 1720w will be enough to power these cards, ive heard they are about 250w each when undervolted so gpu's will total 1500w

so that leaves 220w to run cpu (55w) + ram + mobo, i wont have a hard drive as i will be running from usb stick and no fans apart from cpu cooler

i also need to find out which cards should be connected to each psu, each card requires 2 x 8 pin connectors

should i run the motherboard 24pin and 2 cards from one psu and 4 cards from the other psu
or
should i run 3 cards from each psu
or
should i use 1x8 pin from each psu on each card?

i dont have powered risers, can i solder a molex connector to my un powered ones? or will the motherboard be able to handle the power of 6 gpu's?

any help would be much appreciated, im just trying to figure out possible problems before hand so i can piece the thing together fairly swiftly when the rest of the bits arrive

[BTCNations]

Better use 3rd PSU for safety, if overclocked and with powered risers they can draw more.

[boondock66]

im thinking of undervolting rather than overclocking, to use less power, i think my power bill will go up by £120 per month if running 24h

do i run the risk of damaging any components by not having enough power, or will my system just shutdown?

[aznatama]

your power supply should trip an internal breaker and shut down if power draw is too high.  You need to find out how many rails your PSUs have, and what amp each rail is to determine how many video cards you can run off each rail.

[boondock66]

ok so each psu has a single 71a +12v rail

looking at this website http://www.kitguru.net/components/graphic-cards/zardon/sapphire-r9-280x-vapor-x-review/20/

each card draws 251w on furmark test, will this be similar to running mining software? call it 260w

so 260w/12v = 21.7a

71a / 21.7a = 3.27 gpu's per power supply

so i guess this means i will have to run 3 cards on each psu  so 71a-3x21.7a = 5.9a spare on each psu
so both psu combined = 11.8a at 12v = 141w to run cpu + ram + mobo

i assume that the add2psu will even out the remaining load between each psu as if only one psu was left to power the cpu + ram + mobo only 70w would be availiable

so on paper it seems to work out if the above info and calculations are correct, although a little tight

but most people seem to be saying im gonna need 2 x 1000w+ power supplies

after reading more about the psu i have found this comment in a review :

"As our testing has highlighted, both units when pushed hard will deliver much more wattage than their rating suggests. The Corsair AX860 managed to hold a 1000W load for quite some time which highlights that the internal design is pleasingly over specified."

[aznatama]

add2psu looks like an overpriced gimmick.  Molex connector to trip what appears to be a pbc mounted relay.  Relay shorts the "on" wired for the ATX connector, thus turning on the other PSU.

There's no way it can load balance.

Also, you need to factor in efficiency of the PSU.  if it's rated/tested at 90% efficient, then your 71a can only sustain 62.9a under full load.
Also, powering up may spike the current draw above that, making your PSU trip it's internal breaker and shut down, or blow a fuse/burn out something if it doesn't have an internal breaker.

Sounds like you need a better power supply.  I'd go with a 1250 seasonic to power 4 GPUs, and use one of your existing ones to power the remaining 2 + system.

What power supply do you have?

[boondock66]

MY PSU is a Corsair AX 860 on the box it says it can run at 5.5 amps on 240v which equals 1320watts , isnt the efficiency already factored in to the 71 amps?

[melmo]

I had a 3x7970 rig, undervolted, that was drawing about 750 watts from the wall.  Without undervolting it would easily go up to around 900 watts. 

So it depends on your plans, are you going to try to overvolt and clock them up to maximize your hash rate, or are you going to try to maximize your hash/watt? 

[Samir_H]

Undervolt is a must do with that PSU. CPU wont use 55W, it's gonna be less. Run 3 cards with each PSU.

It's very important to keep all components as cold as possible because you have to be efficient.
Efficiency is higher on lower temperatures, especially take care of PSU and I think it will work.

[Raw-H]

I suggest take 1 1000W psu and one 860 psu. Both for 3 cards but the 1000watt for the system aswell.

Also take in consideration that your psu's efficiency is lower if it's running at 90/100%.

[aznatama]

You can always try it.  Worst that can happen is that you aren't able to run all your GPU's and have to unplug one while you wait for a larger PSU.

I wouldn't bother with those add2psu thigs, overpriced compared to a paperclip or a simple y-splitter.

If this is a BTC/LTC mining only rig, then CPU won't draw much power.   However, you might as well mine proto w/ cpu as well.

[Samir_H]

Tried 3x290 on 850W PSU. I had to undervolt and underclock cards to get 820W at wall.
That was too much but 3x280X can work with that PSU because they need less power.

[takagari]

If the Add2psu is a gimick what's the best option to trip it on?

[Jama]

If the Add2psu is a gimick what's the best option to trip it on?

A paperclip, metal staple, short length of wire etc....
You only need to connect the green wire to one of the black ones on the 24 pin plug.

[aznatama]

If the Add2psu is a gimick what's the best option to trip it on?

A paperclip, metal staple, short length of wire etc....
You only need to connect the green wire to one of the black ones on the 24 pin plug.

^ this

Or, if you really want to b "neat," you could just use a 2-1 splitter for the ATX connector, which is ~$10.  But a paper clip or short length of solid wire is really your cheapest alternative.

[ssateneth]

Also, you need to factor in efficiency of the PSU.  if it's rated/tested at 90% efficient, then your 71a can only sustain 62.9a under full load.

Um, what? The efficiency relates to the conversion of alternating current to direct current + waste heat. If a power supply is rated for 1200 watts, 87% efficiency @ 100% load (80plus gold), then it will pull in 1379 watts at the wall, and output 1200 watts DC and 179 watts worth of waste heat. The efficiency has -nothing- to do with the rated DC output amperage. If it says 71 amps @ 12v on the label, it will do 71 amps @ 12v.

[aznatama]

Oh?  I thought the wattage was rated before the efficiency... hmmm oh well, guess one learns new things everyday.

afaik, most power supplies run most efficient at under 90% load anyways.

[darksoft]

The add2psu works fantastic. I won't bet my $2k plus rigs on a paperclip.

[Samir_H]

Also, you need to factor in efficiency of the PSU.  if it's rated/tested at 90% efficient, then your 71a can only sustain 62.9a under full load.

Um, what? The efficiency relates to the conversion of alternating current to direct current + waste heat. If a power supply is rated for 1200 watts, 87% efficiency @ 100% load (80plus gold), then it will pull in 1379 watts at the wall, and output 1200 watts DC and 179 watts worth of waste heat. The efficiency has -nothing- to do with the rated DC output amperage. If it says 71 amps @ 12v on the label, it will do 71 amps @ 12v.

Hmm, thx for clearing this out.