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GPU power draw question: 75w card w/ a 6 pin?

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Posted · Original PosterOP

So, I put together a build for my buddy off of an old ebay prebuilt and a gtx 750ti that I had laying around. It came with the usual crappy dell (275w, i think) psu, but this time, it had basically NO connectors to spare. I brought my 2x molex to 6 pin adapters w/ me bc I knew the card wouldn't boot unless it had power to the 6 pin connecter, but I also knew that 750tis were 75w cards, so it didn't really matter where that 6 pin power came from. but that's the issue, this psu had a 24 pin, a 4 pin (cpu), 2 sata daisy chained by the dvd drive, and 2 sata daisy chained by the hdd. This left a whopping TWO sata connectors unused. No molex, no floppy, and obviously no pcie power left over.

 

I ended up having to use my psu that I was planning on using in a future build on his computer, but now I'd really like to get it back, if possible. due to the AWFUL assortment of connectors from the psu, the only thing I have left to power the gpu with would be a sata (or 2x sata) to 6 pin adapter. Now, I now this is usually a bad plan, and I know you guys are gonna say "just buy a cheap psu", but the slot provides 75w and the card has a 75w tdp, and the rest of the system is MAYBE 90W at full load, so I really don't feel like investing extra money into this super low end budget built and the psu has almost double the wattage required (275w psu vs ~165w max draw which I'd honestly estimate to be closer to 140-150 after I undervolt the gpu)

 

My question is this, what is the sequence in which the card draws power? ie, when idling (say 15w power draw), does it draw 15w from the slot? or maybe 10 from the slot and 5 from connector? how about at full load (75w)? does it draw all 75w from the slot, or maybe 32.5 from the slot and 32.5 from the adapter?

 

Basically I want to know if I'm ever at risk of drawing more than 5-10w from the adapter, bc I know it could supply at least that much and I'd like to stay safe.

 

Keep in mind, I plan to undervolt just to ensure that it never exceeds or even gets close to its 75w tdp.

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The 750 Ti will only draw its power from the slot at a max of 75W. Your PCIe slot should be able to provide the necessary power for the card. 

3 minutes ago, sparkythewildcat said:

I know you guys are gonna say "just buy a cheap psu", but the slot provides 75w and the card has a 75w tdp,

You read my mind and that works too. 


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What 750 Ti are you using that has a 6-pin attached?


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Some 750 Ti's have a TDP from the factory of 75W, so when they are at factory speeds, they only use 75W. However, when overclocked, they use a little bit more than 75W, so they have an extra connector for power. I don't know the reason on why they don't turn on without the 6-pin, but the 6-pin is definitely for more power.


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1 hour ago, sparkythewildcat said:

crappy dell (275w, i think) psu

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giphy.gif

 

1 hour ago, sparkythewildcat said:

2x molex to 6 pin adapters

Spoiler

giphy.gif

 

 

1 hour ago, sparkythewildcat said:

gtx 750ti

Spoiler

atomic-mushroom-cloud-explosion-2-2-gif.

 

 

All seriousness now. I think you should replace the PSU anyway because those cheap ones are really terrible and could fry the hardware/the building it's in. It might cost some more budget but it's better to do it now than to realize later "oh shit I wish I'd done that, now my CPU and GPU are toast".


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75w tdp doesn't equal 75w power draw. For example, my Ryzen 5 1600 has a 65w tdp, but uses 80w of power according to hwinfo64.


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Posted · Original PosterOP
On 11/14/2017 at 1:25 PM, thegreengamers said:

75w tdp doesn't equal 75w power draw. For example, my Ryzen 5 1600 has a 65w tdp, but uses 80w of power according to hwinfo64.

I know it doesn't exactly match power draw, but it roughly estimates it and it's all I have to go off of aside from their "400w PSU" requirement which is obviously way more than necessary for most 750ti systems

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Posted · Original PosterOP
On 11/14/2017 at 1:25 PM, thegreengamers said:

75w tdp doesn't equal 75w power draw. For example, my Ryzen 5 1600 has a 65w tdp, but uses 80w of power according to hwinfo64.

Also, while this is true, I know that 750tis usually do operate off of the pcie slot alone, so I know the gpu is designed with the 75w limit alone and the additional connector was added for OC headroom. I just need to know whether it will default to drawing it's power from the slot then start drawing from the connector after it's maxed the draw from the slot, or if it does something else.

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