Power delivery issues with Supermicro BPN-SAS3-846EL1 backplane/CSE-846

PaperBlankets

New Member
Sep 6, 2019
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Hi there, I've been building out a shallow 24 bay DAS for my rack.

It's based on a Supermicro BPN-SAS3-846EL1 from a CSE-846.
I have seen quite a few builds of others using non standard PSUs in a CSE-846, without issues (link) so I didn't really think anything of it when I removed the backplane, built out an enclosure and attempted to power it with standard PSUs.
I believe I am having an issue with 5v power delivery; but it could be 12v.

So far I have tried the following power supply combinations:

PSUwattage on 5v railAmps on 12v railAmps on 5v railBehavior
2x Supermicro PWS-920P-SQ500w?100aWorks as expected/all drives behave
FSP Hydro G PRO 850W120w72A20Asome drives are not recognized in unraid, read/write errors
FSP Group FSP550-50SGGBA120w45A22A*
FSP Hydro G PRO 850W & FSP550-50SGGBA240w?107A?42A?*



I currently have 20 drives in use, so it makes sense that the power draw is pretty high, but I have not found any info on the recommended psu specs for this backplane (Manual here: https://www.supermicro.com/manuals/other/BPN-SAS3-846EL1-N8.pdf)

The backplane seems to start fine in all 4 configurations, the leds light as expected/pass 5v and 12v power checks on start.

Can anyone with this backplane point me to the PSU they are using? How many drives they are running?
 

kapone

Well-Known Member
May 23, 2015
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I can't speak for the SAS3 backplane, but I use 'customized' 846 disk shelves as well. They use HP PDBs and their platinum PSUs. I can power 24x HGST SAS3 7200rpm drives in a SAS2 based backplane, with a single HP 460w (these are pretty underrated) PSU and a single HP PDB.

The PDBs are rated for ~20a on the 5v rail.
 

PaperBlankets

New Member
Sep 6, 2019
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@i386 Yeah I was thinking an 850w PSU that can do 20+amps on the 5v rail would be plenty. :/

I can't speak for the SAS3 backplane, but I use 'customized' 846 disk shelves as well. They use HP PDBs and their platinum PSUs. I can power 24x HGST SAS3 7200rpm drives in a SAS2 based backplane, with a single HP 460w (these are pretty underrated) PSU and a single HP PDB.

The PDBs are rated for ~20a on the 5v rail.
Thanks for that info. This was my thinking as I stared this "20a should be plenty".
This backplane has 6 molex connectors.
 

PaperBlankets

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Sep 6, 2019
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So does the SAS2 version. That should have no effect. It's just wires...whether 6 or 12 or however many. They all go to the same source.
I don't think it's the issue either, I just brought it up because each molex connection is only rated for 40W so based on the power delivery layout (A psu with a single 4 pin molex connection or something) it _could_ be the limiting factor. For the setups above though I used the exact same connection layout across the 4 setups 3 molex extenders to the PSUs, to distribute the power evenly.) so I would not think that would be the issue since this setup is working with the supermicro PSU and PDB.
 

kapone

Well-Known Member
May 23, 2015
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I don't think it's the issue either, I just brought it up because each molex connection is only rated for 40W so based on the power delivery layout (A psu with a single 4 pin molex connection or something) it _could_ be the limiting factor. For the setups above though I used the exact same connection layout across the 4 setups 3 molex extenders to the PSUs, to distribute the power evenly.) so I would not think that would be the issue since this setup is working with the supermicro PSU and PDB.
That power rating is news to me...as far as I knew, each pin in the molex connector is rated for 11 amps. i.e. ~130w on the 12v pin and ~55w on the 5v pin. With 6x molex going to the backplane...

Screen Shot 2021-02-17 at 4.05.12 PM.png
 

PaperBlankets

New Member
Sep 6, 2019
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I think that's 100% correct.
If I'm remembering right I was thinking less because I have a molex splitter that looks smaller than 18 AWG that powers a fan controller + fans in the enclosure and I was trying to account for that; but at any rate 55w for the 5v line sounds right. :thumbsup"
 

ericloewe

New Member
Apr 24, 2017
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That power rating is news to me...as far as I knew, each pin in the molex connector is rated for 11 amps. i.e. ~130w on the 12v pin and ~55w on the 5v pin. With 6x molex going to the backplane...

View attachment 17566
Nitpick: The connector design is rated for 11 A, but many connectors are often rated for less (~5 A).