Cooling System, Temperatures, Overclocking and Power Consumption
The cards have the same cooling system. Being far from innovative, the cooler consists of a plastic casing, a GPU heatsink and a metallic plate with blower.
The metallic plate helps cool the power circuit components and memory chips via thermal pads.
Some of the components are directly cooled by the blower through the slits in the plate.
As for the GPU heatsink, it consists of a solid copper base, copper heat pipes and aluminum fins which are soldered to the base and pierced by the pipes.
The two outermost heat pipes are 6 millimeters in diameter. The central pipe is 8 millimeters in diameter. All the elements are soldered to each other in this cooler.
The 70mm fan is the same PVB070G12N model from Foxconn on both cards. It runs on a dual ball bearing.
The speed of the fan is PWM-regulated from 1000 to 5700 RPM. Fortunately, the fans never got higher than 2050 RPM during our tests.
We checked out the cards’ temperature while running Aliens vs. Predator (2010) in five cycles at the highest settings (2560x1600, with 16x anisotropic filtering and 4x antialiasing). We used MSI Afterburner 2.2.0 Beta 14 and GPU-Z 0.5.9 as monitoring tools. This test was carried out with a closed system case at an ambient temperature of 26°C. We didn’t change the cards’ default thermal interface.
Let’s see how efficient the coolers are with the fan regulated automatically and at the maximum speed:
So, the GPU temperature of the AMD Radeon HD 7870 was as high as 76°C in the automatic mode, the fan reaching a top speed of 2030 RPM. The HD 7850 was only 69°C hot at a speed of 1700 RPM. This might be expected considering the identical coolers and the cards’ GPU specs. When the fans worked at the maximum speed, the GPU temperature of each card was no higher than 51°C, but, of course, the fans were unbearably noisy at 5700 RPM. We don’t know the reason for AMD to have chosen such high-speed fans. A fan with a rated speed of 3000 RPM would be quite enough.
Then we measured the level of noise using an electronic noise-level meter CENTER-321 in a closed and quiet room about 20 sq. meters large. The noise-level meter was set on a tripod at a distance of 15 centimeters from the graphics card which was installed on an open testbed. The mainboard with the graphics card was placed at an edge of a desk on a foam-rubber tray.
The bottom limit of our noise-level meter is 29.8 dBA whereas the subjectively comfortable (not low, but comfortable) level of noise when measured from that distance is about 36 dBA. The speed of the graphics card’s fans was being adjusted by means of a controller that changed the supply voltage in steps of 0.5 V.
We’ve included the results of a reference AMD Radeon HD 7970 in the next diagram for the sake of comparison:
The cooling system installed on the Radeon HD 7870 and HD 7850 is quieter than the reference Radeon HD 7970 cooler as is indicated by the noise level graphs as well as by the vertical dotted lines which mark the speed range of the fans in the automatic regulation mode. It doesn’t mean that the new cards are really quiet, though. Each of them was audible against the background noise of our quiet testbed in 3D mode.
We tried to overclock our cards with their default coolers and at their default voltages. The Radeon HD 7870 was stable at a GPU clock rate of 1190 MHz (+19%) while the HD 7850, at 1050 MHz (+22.1%).
The memory chips of every card refused to be clocked higher than 5800 MHz, which is +21% to their default clock rate. Hopefully, off-the-shelf samples will be more overclocker-friendly.
Here is the temperature of the overclocked cards:
The GPU temperature of the overclocked AMD Radeon HD 7870 grew by a mere 3°C, the top speed of the fan increasing from 2030 to 2200 RPM. The Radeon HD 7850 got hotter by 9°C and its fan accelerated by 370 RPM compared to the non-overclocked mode.
Next we measured the power consumption of computer systems with different graphics cards using a multifunctional panel Zalman ZM-MFC3 which can report how much power a computer (the monitor not included) draws from a wall socket. There were two test modes: 2D (editing documents in Microsoft Word and web surfing) and 3D (the benchmark from Metro 2033: The Last Refuge at 1920x1080 with maximum settings). Here are the results:
It’s clear that the systems with the new AMD Radeon HD 7870 and 7850 cards are the most economical ones, consuming no more than 425 watts even if the graphics card is overclocked. Take note that these two systems differ by a mere 5 watts from each other but the difference from the Radeon HD 7950 system is 30 watts. Of course, Nvidia’s solutions and AMD’s previous generation card need more power than AMD’s Tahiti and Pitcairn-based products.