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# Watt measuring and power supply need

Member Posts: 12
Hello,
I have a minor rig with two video cards running. My power supply supports 750 Watt, and it is in the Gold category when it comes to being energy friendly. Out of curiosity I bought this tool to measure the amount of energy my rig actually uses (puts it into the connector, followed by the computer plug). According to this tool my rig uses a total of 170 Watt. Is that so? If I add two-three more video cards and this tool will say 650 Watt, is that safe then to use, and the power supply should be enough for that?

Ps: I use two poor graphic cards for mining, two pieces of Gigabyte GeForce GTX 1050 Ti OC 4G 4GB. Of course I want to add more cards to the rig, and that is why I am asking....

Or is there something about the power supply being energy friendly, and the graphic cards actually use a higher amount of watt, but the power supply somehow minimize it? I am totally new to this and that is why I am asking.

• Member Posts: 29
edited August 2017
Frist, The number youre reading is probably correct, but understand this changes on demand. If you were not looking at the power draw while the gpus were under max load, then thats not an accurate representation of the power draw.just want to make sure you're not calculating based on less than a max load..

Power supply efficiency determines the amount of excess electricity that is drawn from the wall. Let's say your have 1 gpu takes 100 watts to run. A super efficient power supply might pull 102 watts at the wall. A less efficient psu might pull 120 watts. So on and so forth.

Also, the closer to max load you push a power supply the less efficient they are - that is why most will try to keep it 50-60% under max load - to minimize the amount of excess electricity drawn.

Also... the amount of amperage on the 12v rail is important. Cheaper power supplies cheat you by boasting large watt numbers, only to find out its because they have more 12v rails. And less amps per rail. You want more amps per rail, preferably all amps on a single rail...

But anyway, you might be okay.. if the cards demand 650 watts... count maybe another 40 for everything else for a total of 690, and then inefficiency of probably about 60 watts or so, you will be cutting it real close. And definitely won't be getting your gold rated efficiency... unfortunately that efficiency starts to fall off after 50-60% load.

Hope that helps!

EDIT::
Sorry, just realized you said "... and this tool will say 650 Watt, is that safe then ..." - yes, if the tool is reading less watts than what the power supply is rated at - you're safe. All the hooplah above was just to help you keep in mind the closer to a power supplies limits you are, the less efficient it becomes.
Post edited by FirstnameBeau on
• Member Posts: 12
Thank you for this reply... You absolutely answered my question, and I am really grateful!
• Member Posts: 29