PCIe power limit

Rubb · April 1, 2022

Hello!

I have an Acer Aspire TC-380 pre-built, with a Ryzen 5 2400G, and only integrated graphics. I wanted a small GPU for some light gaming and I settled on the Biostar RX550 4GB, which is enough for my needs, so I proceeded to upgrade the PSU with a Corsair CV550, and finally plug the GPU in.

Now, the RX550 doesn't require a PSU connector (in fact, it doesn't have one at all), and only draws power from the PCIe, but I noticed, after monitoring it a bit because of some stutters, that it only draws up to 25 W, whilst in reality it should have, by PCIe standards, up to 75 W available.

I have been looking around for days, and as a matter of fact I keep finding this text copy-pasted from Wikipedia in every post similar to mine:

Quote

All PCI express cards may consume up to 3 A at +3.3 V (9.9 W). The amount of +12 V and total power they may consume depends on the type of card:^[26]^: 35–36^[27]

×1 cards are limited to 0.5 A at +12 V (6 W) and 10 W combined.

×4 and wider cards are limited to 2.1 A at +12 V (25 W) and 25 W combined.

A full-sized ×1 card may draw up to the 25 W limits after initialization and software configuration as a "high power device".

A full-sized ×16 graphics card^[22] may draw up to 5.5 A at +12 V (66 W) and 75 W combined after initialization and software configuration as a "high power device".

But noone seems to tell me how to actually configure the card as a "high power device". I supposed it was something internal to the card, but mine doesn't seem to do it.

Also, I read that some mobos have hardwired limitations on how much power can be drawn from PCIes, but they all seem to have it clearly written on the mobo itself, whilst mine doesn't present anything around it indicating the limitation, that's why I think it is a problem that could be solved via software.

I already disabled the PCIe Power Management / Saving thing in the advanced power combination options, but that didn't work.

Also thought about risers, but then again, riser cards I can find only connect via PCIe x1 to the mobo, and that would bottleneck it heavily if I'm not mistaken, and the only other thing I found is some kind of almost homemade riser cable with molex connector from moddiy.

Can anyone help?

mariushm · April 1, 2022

The MAXIMUM a RX 550 would consume is 45 watts .... there's literally not enough gpu chip to consume more than that.

If you think your card is limited by the slot, get a pci-e riser cable with separate power input, which will power the video card from a molex / pci-e 6 pin instead of the slot.

For example : https://www.amazon.com/Extension-SinLoon-Flexible-Extender-Ethereum/dp/B07BNF4D9Q/

Rubb · April 1, 2022

59 minutes ago, mariushm said:

The MAXIMUM a RX 550 would consume is 45 watts .... there's literally not enough gpu chip to consume more than that.

If you think your card is limited by the slot, get a pci-e riser cable with separate power input, which will power the video card from a molex / pci-e 6 pin instead of the slot.

For example : https://www.amazon.com/Extension-SinLoon-Flexible-Extender-Ethereum/dp/B07BNF4D9Q/

It says

Quote

3.Support PCIe 1X card and 8X,16X card( only provide 1X speed).;- Extra molex(12V/GND) power supply for PCI-e video card.

Doesn't it mean that it is 1X bottlenecked?

mariushm · April 1, 2022

Where the hell do you read (only provide 1x speed)?

If it was x1 riser, they wouldn't have put that wide ribbon cable on it. It's a x16 riser cable in my Amazon link, and the description says you can insert x1, x4 ,x8 or x16 cards in the slot or the riser cable ... and it will work because that's how pci-e is designed.

The RX550 and RX560 (and RX 460) are maximum pci-e 3.0 x8 by the way, they come with a x16 slot that's half unused because people are stupid and would return video cards because the card doesn't fill the x16 slot, or would not buy because they don't have pci-e x8 slot in their system.

The part before the notch is only power (12v and 3.3v) and reset / standby / debug signals and the part after the notch is modular, up to 16 pci-e lanes, around 6-8 contacts for each pci-e lane... you should be able to tell on the video card because theres longer ground traces separating the groups.