PSU advice: how much Watt do I need? RX 470

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vinny9561

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Feb 2, 2015
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Hey everybody,

I don't have any recent experience in setting up a gaming pc. I wanted to hear who could advize me the required PSU.

Right now I have a basic PC , which is drawing 70-80Watt off the wall when the CPU is 100%.
The PSU that's in it states: maximum continuous load: 300 W.

I have ordered a new GPU (RX 470 8 GB Gaming X), MSI says they draw 150 Watt, but they recommend a 500W PSU.

If I add 70W + 150W = 230 Watt , which should still be fine with the 300 W PSU, no? Do I need to buy a new PSU? I don't have any experience with this, any advice is highly welcome.

PS: I'm not really planning to use the PC for gaming. I bought the GPU to have a more smooth sketchup 3d drawing experience and I want to do some mining as well.

Thanks!
 
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Power supplies aren't really meant to be run at full load. So let's say you have a CPU that draws 65W, and the 470 draws up to 150W, that's 215W right there for just those two things. Round it up to 250W when you add in the other items in your computer. Some of this power is on the 3V and 5V outputs, some on the 12V output. So you don't really have a full 300W available for each component. The 12V components might have something like 216W available to them, with the rest on the other outputs. See the problem?

In addition, not all power supplies provide the rated power under continuous use. It might be a peak "For just one moment in the lab when the moon was full" power rating. Not only that, but power supplies work best at a percentage...
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vinny9561

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I appreciate your comment and it's what I expected after doing some research.

However, I don't understand the math :
if my system only draws 230W , and the PSU can deliver 300W continous (not peak), why would that not be sufficient?
 
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turkey3_scratch

turkey3_scratch

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Well the wattage of a power supply unit is basically marketing, there is no standard by which they actually rate these power supplies, there is no measurable value called "the wattage of a power supply", so it just leaves people like you confused.

The PSU in your computer is probably some cheap thing that's not very good. If you had a quality 300W unit that had the proper cables and everything (and they don't really exist), you would be perfectly fine, really we'd have to know the brand/model of your PSU to make determinations on its quality.

Usually you can't buy good PSUs under 450W for a good price.
 
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Dark Lord of Tech

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And I also doubt that low wattage PSU has the 6+2 to run the card.
Time for an upgrade.
 
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vinny9561

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Thanks for the insight. Here is the psu i'm talking about:

8HxC3tApt.jpg


http://pasteboard.co/8HxC3tApt.jpg
 
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dontlistentome

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Sep 5, 2016
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Power supplies aren't really meant to be run at full load. So let's say you have a CPU that draws 65W, and the 470 draws up to 150W, that's 215W right there for just those two things. Round it up to 250W when you add in the other items in your computer. Some of this power is on the 3V and 5V outputs, some on the 12V output. So you don't really have a full 300W available for each component. The 12V components might have something like 216W available to them, with the rest on the other outputs. See the problem?

In addition, not all power supplies provide the rated power under continuous use. It might be a peak "For just one moment in the lab when the moon was full" power rating. Not only that, but power supplies work best at a percentage of max load. You don't want to run a 300W with 300W load even if it could put out that much power. I'd aim for 60-80% load, since generally this is the sweet spot for power supplies and it leaves a bit of head room in case y9u add/upgrade a component.

edit: that power supply has 17A on the 12V output. That gives you just over 200W to use for the CPU and videocard= not enough
 
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turkey3_scratch

turkey3_scratch

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The PSUs you are describing are all old or crappy stuff though (12V rating lower than rated wattage, being rated by peak vs continuous). Any modern day good PSU can be run at full load fine. Additionally, the 3.3V and 5V rails these days use like 10-20W of power generally at most.
 
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dontlistentome

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You haven't seen the image he linked, have you?
 
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turkey3_scratch

turkey3_scratch

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I'm talking about the generalized statement you made that "power supplies aren't really meant to be run at full load". This is not necessarily true. Many power supplies are even underrated. It really depends on what PSU we are talking about.
 
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