The 7950 series graphics cards draw 200w – 250w under load. The 7950 graphics cards draw at least 190w on a weak factory OC to 900mhz. Under stress and with overclocking, they can easily reach the 7970’s 250w total power draw. While it is quite possible to stay under 200w, if you are going for the highest hashrate, plan your PSU to account for 250w for each card. It’s better to be safe and your PSUs will also last longer if you don’t max them out.If you’re using Gold rated power supply units (PSUs), then a 1000w PSU should be enough for 3 cards. If you’re using a budget / low power CPU (like Intel S and T or Celeron processors) then you should be fine as processors like the i5 only consume about 35 watts.
Various PSU Tips for Mining Rigs & 7-series Cards
- There are always slight variations with cards and their power requirements. For example, a rig with four 7970 that are overclocked by 100mhz will draw 1130 watts at the wall.
- For 7950 graphics cards, stick with Gigabyte Sapphire Radeons as they are easy to overclock.
- As mentioned earlier, the i5 Intel CPU is a good choice as your rig’s processor since it draws only 35 watts. Also stick with SSD drives as they draw less power compared to spinning hard drives.
- Keep in mind all the other smaller components that are drawing energy, especially your case fans. The graphics cards themselves require powered connectors to the motherboard, and each PCIE connector will draw between 10 and 12 amps at 12v.
- Remember that PSUs are rated for how much power that they deliver to components, not how much that they pull at the wall. A 90% efficient 1200 watt PSU is rated to safely pull up to 1333 watts at the wall (1200 / .9). This is why a high-efficiency unit is so worthwhile and will save you money in the long run. A lower efficiency unit will pull more at the wall to deliver the same amount of power to components.
One Versus Two Power Supplies for Mining Rigs
It’s preferable in many instances to have 2 power supplies instead of 1 when running a mining rig. Some of the benefits of a multi-psu mining rig include:
- The closer you are to the max wattage limit of your PSU, the less efficient it becomes. That means wasted energy which just costs money, adds heat and doesn’t contribute as much as a non-maxed out PSU.
- You may have calculated your power requirements to be below that of your PSU, but keep in mind that starting up your computer will cause a one-time spike that could max out your PSU.
There are as well a few drawbacks of having multiple PSUs:
- One PSU should be able to provide more stable power to your graphics card, which might help their longevity.
- It’s one more point of failure for your rig. This could be a plus or a minus: some people might want two power supplies so that they can still mine a lower-powered algorithm (like DarkCoin or X11Coin’s X11 algorithm) should one power supply go belly-up.
- Definitely less hassle to setup as you won’t need to bridge your power supplies when running only one PSU for your mining rig.
Here’s an example 7950 mining rig using one fairly robust (1200w) power supply to power the rig:
The rig uses a single 1200w LEPA PSU to power 4 MSI Radeon 7950 Graphic Cards.
And here’s an example of a R9 270X mining rig that uses dual power supplies:
- Corsair CX600M 600 Watt Power Supply
- Corsair CX750 700 Watt Power Supply
As always, I recommend checking out GAW Miners if you want premium hashing power that draws less energy than traditional graphics card based mining rigs.