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AMD Threadripper System Buyer's Guide

By: Steven Bassiri | Guides | Posted: Oct 4, 2017 3:55 pm

Choose Your Power Supply

 

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I measured total system power consumption at the wall with the CPU overclocked to 4GHz and at stock and compiled the results. I tested with synthetics Intel Burn Test and Furmark (max CPU and GPU load), Rise of the Tomb Raider (typical game), GTA:V (typical game), Ashes of the Singularity (very resource intensive game), Intel Burn Test alone (CPU intensive only), CINEBENCH (typical CPU rendering load), and HandBrake (typical CPU transcoding load). We can see that at full synthetic CPU load, the CPU VRM itself can easily pull over 300-350W at 4GHz (CPU pulls a bit less due to VRM), and that number will go up or down depending on the VRM quality and CPU/VRM temperatures.

 

 

I was pulling a maximum of 629W with my single GTX 1080Ti, single M.2 SSD, and 1950X overclocked to 4GHz. I would recommend an 850W PSU as a minimum by these results, and over 1000W if you are going to have more than one GPU or many drives and fans. However, wattage isn't everything, the PSU rails also matter. In the case above, the CPU at 4Ghz was pulling 300-350W from the 12v rail attached to it, and that can become an issue with multi-rail PSUs.

 

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Multi-rail PSUs used to be very common a few years ago, and sometimes vendors didn't balance them correctly with the connections they fed. Let's say your power supply has a 100A single rail (the one on the right does), and there is a short on the motherboard that the PSU or motherboard doesn't detect. In that situation, the short would pull 100A into the system until the power supply's internal over current protection (OCP) kicks in, and that would definitely fry your system components including your CPU and perhaps your GPU. To counter this, vendors have gone and divided up that single 100A rail into multiple smaller ones, let's say five 20A rails.

 

If the short happened inside your motherboard and it was only allotted 20A, then perhaps only your motherboard would have died instead of your CPU and GPU and motherboard, as the power supply would have caught it at the 20A trip point. We can see that the PSU on the right has divided up a 1500W rail (125A at 12v) into six rails, two of which are 20A and four of which are 30A. The 20A rail would support up to 240W (12V at 20A) and the 30A rail at 360W (12V at 20A) before they tripped OCP on the PSU and caused a shutdown. However, you can hit those limits naturally through the CPU or GPU. The truth is you don't typically see 20A rails these days, but you should keep an eye out for them, especially on a low power (<1000W) PSU with multiple rails. If the CPU is provided a single 20A or 30A 12v rail with the 1500W PSU, it could cause issues while the 1200W PSU on the right with a single 100A rail wouldn't cause issues.

 

If the CPU is pulling 350W (CPU pulls from 12v only), then a 20A single rail could cause major overclocking issues, as could the 360W rail. Typically, vendors will make sure that the CPU power connectors get the larger rails, but not always, as CPUs like Threadripper haven't been common in the past few years. I recommend looking for single rail PSUs or large 30-40A multi-rail PSUs to avoid overclocking issues.

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