ASRock Rack SIENAD8-2L2T ATX power connectors?

Hardware Hub Motherboards
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Hi, I’m putting together my new server with the ASRock Rack SIENAD8-2L2T motherboard. In the spec sheet it says it uses a 24pin to 4pin converter plus 2 x ATX12V 8pin connectors. I bought a Seasonic 850W ATX3 PSU with these connectors.

I now find a third (horisontal) 8pin ATV12V connector on the motherboard, so in total the 4pin connector, plus ATX12V1, ATX12V2 and ATX12V3, which I don’t have connectors for. Is the ATX12V3 needed, do I have to connect power to it?

PS. I have also contacted ASRock Rack support.

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My guess is that ATX12V3 is primarily for the PCIe slots, the other two for the CPU.

Which CPU are you using? If its one of the lower TDP ones you might be able to ditch ATX12V2. Or you might ditch ATX12V3 if you don’t have a ton of PCIe slots used.

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I have the 8434P. I won’t run any power heavy PCIe initially, only M.2 bifurcation cards.

I booted without PCIe board, just 8 fans and 1 boot M.2 using ATX12V1 and ATX12V2 and it installed and boots Proxmox ok so far.

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With that CPU I wouldn’t recommend only using one 8-pin ATX power.

Remember that every PCIe slot can use up to 75W (no matter if the device has it’s own PCIe power connector).
So even if you fill every slot with a lumpy GbE NIC for some reason, that third 8-pin should be used. Those M.2 bifurcators have to supply the power to those SSDs, and depending on what you are going to use, 5-10W per SSD is not unreasonable to calculate with.

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I’m using two 8pin connectors. The spec says:

“Power Connector 1 (4-pin, ATX PSU signal) w/ ATX 24-pin adapter cable, 2 (8-pin, ATX 12V)”

I’ve connected those two 8pins. The third one is only mentioned in the manual. Weird.

I guess I’ll have to buy an extra 8pin CPU cable for the PSU, it came with 2xCPU and 3xPCIe 8pin connectors.

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You were right, I got this reply from ASRock Rack:

"If you want to use PCIE slot, it is recommended to use the ATX12V3 connector to ensure sufficient power supply.

Otherwise you can only use ATX12V1 and ATX12V2 connector"

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So for your PSU you linked above I assume you used the ATX cable thing from ASRock in the box:

image

And then from your PSU the two CPU connectors shown below:

image
image1222×229 15.9 KB

Is that right?

What did you do for the 3rd power plug for PCIe? Would it have been one of the PCIe power plugs from your PSU kit?

1 Like
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The third can be left unplugged if you aren’t going to be using the pcie slots for much. If you are drawing more than 50w from the slots I would definitely recommend getting that third one connected.

You can use 2x8 pin pcie to 8 pin cpu to use a standard psu with these

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I first connected the 1x 4pin and 2x 8pin CPU power connectors mentioned in the ASRock spec. For the third 8pin CPU power connector driving the PCIe slots I just bought a third 8pin CPU cable for my Seasonic PSU. It’s modular and has 5x 8pin connectors for PCIe or CPU, depending on cable you use. (Plus the connector for the 24pin).