Radeon 7990 - same rigs, different temperature.

[dzzima]

I have two scrypt rigs, each 2x7990. They are very similar - identical MBs, ram, CPU, chassis, fans, OS, drivers. The only noticeable difference is the PSU - 1000 and 1250w. I use the same settings (clocks, voltage) but the rig with 1000w CPU makes both cards approximately 10 degrees hotter. Any ideas why?

[AvalonMiner]

You should check if the 1000W psu is very hot. It must be under a very heavy load. It could be extra heat coming through the cables to those 7990s from that power supply.

[Eastwind]

For the 1000W power supply, it is under strain to supply power to 2X7990. So the efficiency is low, more heat is generated inside the PSU. So the whole system is hotter.

If you take out the PSU from the case, then temperature of the card should drop.

I think you are not using a "Gold" efficiency rated PSU.

If you undervoltage the 7990, power requirement should be lower. Using MSI afterburner Beta 18 or later to reduce the voltage from 1.2V to 1.05V will lower the wattage by 20%.

[dzzima]

Thank you for the recommendations.

I'm using the gold certified OCZ ZX 1000W, current voltage is 1.06, core 1000 memory 1400. I will reduce the voltage to 1.05 and see what happens.

The other story - how much power will 4x290x require? Thanks.

[Gazza1]

The other story - how much power will 4x290x require? Thanks.

I would get a 1500w going by the Furmark Power Consumption Rating
http://www.anandtech.com/show/7457/the-radeon-r9-290x-review/19

[dzzima]

1.05 didn't work, cgminer crashes after some 5-10 minutes. Ok, I will swithch the PSUs and see if it helps.

[Eastwind]

Can you change the memory frequency  to 1000, 1200 or 1250 MHz? That will reduce the power consumption as well.

For some of my set up, I use 1.0V, core/memory = 950/1000MHz. The power consumption is less than 400W per 7990. The hash rate is 660kH/s for each GPU.

For another setup with 4X7990, I use 0.95V, 850/800MHz. The power consumption for the whole system is 1400W. The hash rate is 4.85MH/s.