Gaming Hardware

Why does my PC turn off since I installed a new graphics card?

Good graphics cards are expensive. There is nothing that infuriates a gamer more than having the visual loveliness snatched away in a moment to be left sitting in the dark.

To be clear, I’m talking about a machine shut-down – just as if someone had pulled the power cord out of the back of the PC. No error messages, no warnings – just a dead machine.

I’d put a few pounds on the fact that when you purchased the new GPU, you didn’t pay enough attention to your power supply unit (PSU) – and that’s most likely what’s giving you grief.

Watt?

Let’s be honest, a PSU is the boring bit of a computer that people don’t like to talk about. Their function is to distribute power to the components in your PC, but how this happens changes between models and manufacturers. There are a few things that we need to look at, so let’s begin with your new graphics card. In our example, the problematic upgrade is a GeForce RTX™ 3070 GAMING OC 8G.

GeForce RTX™ 3070 GAMING OC 8G

Take a look at the manufacturer’s specification and you’ll discover that Gigabyte suggests that a 650 watt PSU is required, as well as one 8‎ pin*1 and one 6 pin*1 connector.

Screwdriver time!

Now you know what you need, the next stage is to ascertain what is powering your PC. The easiest way to get this information is to grab a screwdriver and remove the side-panel of your tower. You should find a manufacturer and model number on the side of the PSU. If your PSU has a lower rating than 650w then you can be sure that you’ve discovered the problem – but what if it’s marked at 650w or higher?

A typical 650w PSU

Ohm’s Law

Not all PSUs are created equally – even ones with the same wattage rating. Here is the manufacturer’s specification for a non-branded 650w PSU:

+5V+3.3V+12v-12V
36A30A30A0.5A
360W12.5W
Part specification from a non-branded 650w PSU

The details that we’re interested in is highlighted in red – the 12volt (v) line. This PSU only draws 30 amps (A) on its 12 volt (v) line giving an output of 360w (Ohm’s Law is w = v x a). It’s important to note that the 650w rating is for the entire PSU. This particular unit will fail when more than 360w is drawn from the 12v line. Let’s compare this against a branded PSU:

+5V+3.3V+12v-12V
20A20A54A0.3A
648W15W
Part specification from a branded 650w PSU

Again, looking at the 12v line, it’s clear that this PSU is capable of delivering much more power. Using Ohm’s law: 12v x 54A = 648W.  Though this branded PSU is also rated at 650w, it can deliver 57% more power over its 12v line than the non-branded PSU. That’s a massive 288w in your back pocket to make sure that your machine stays powered on when the system is working at full crank.

Wait – there’s more…

We’ve only focused on the PSU, but all your other components need to be thrown into your calculations too. If you’re building a new system or are looking for a PSU upgrade then use a power consumption calculator to analyse your components and get an idea of what you need to purchase.

Connectors

In our example, Gigabyte told us which connectors were required to power the card. This relates to the physical plugs which connect the PSU to the GPU. It’s important to ascertain if you have enough plugs to deliver adequate power levels. PSU manufacturers provide lots of information about the cables and plugs that come with their products so check this before spending money on a product that’s not going to work.

Check the connectors…

Generally, a more expensive PSU will give greater energy efficiency, modular connections and near silent operation, but it’s important to hit the sweet spot between inadequacy and overkill. Take your time, do your homework and the next time that you’re seconds from victory, perhaps the machine won’t cut out during your moment of glory.

About the author

Lee Grant

I can normally be found attacking things with screwdrivers in my small computer repair business or writing a column for PC Pro magazine.

I am also trying to solve a mystery involving David Bowie.

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