Bought a supermicro 846 and I was hoping to upgrade the power distributor psu

Notice: Page may contain affiliate links for which we may earn a small commission through services like Amazon Affiliates or Skimlinks.

risho

New Member
Sep 3, 2019
10
1
3
It came with a PDB-PT846-8824 power distributor but it doesn't have the connectivity I require. I need at least 2 pci-e 8 pin connectors. All I've got left from this psu is 4 floppy connectors and a cpu connector. I would really prefer to avoid doing dangerous splitter and conversion things. Is there a different power distribution backplane I can get to replace my current one that will have 2 pci-e 8 (6+2 would be even better, but not required) pins and maybe even a couple of sata cables too?

I've found this psu cable list on supermicro's site but it's unclear what is and isn't compatible with my chassis.

If it matters the specific model is Supermicro SuperChassis 846E16-R1200B with the BPN-SAS2-846EL1 backplane that requires 5 or 6 molex cables by itself.

edit: or maybe I should just tear the whole thing out and just jam an atx power supply in there. i would prefer to use something that is natively supportede by the chassis, but it seems like a lot of people like to do that. i also just so happen to have an factory sealed hx1000i just sitting in my closet not doing anything....
 
Last edited:

funkywizard

mmm.... bandwidth.
Jan 15, 2017
848
402
63
USA
ioflood.com
There's an official supermicro cable, 8-pin EPS (CPU) power connector to dual 8-pin gpu power connectors.

Supermicro part number CBL-0424L

Should do the trick.
 
  • Like
Reactions: nikalai

risho

New Member
Sep 3, 2019
10
1
3
After seeing the horror stories of molex to sata cables catching on fire I've become quite skeptical of converter cables also splitting one high power cable into 2 high power cables on the same rail makes me uneasy as well. Is that cable really safe?
 

funkywizard

mmm.... bandwidth.
Jan 15, 2017
848
402
63
USA
ioflood.com
After seeing the horror stories of molex to sata cables catching on fire I've become quite skeptical of converter cables also splitting one high power cable into 2 high power cables on the same rail makes me uneasy as well. Is that cable really safe?
Have used plenty of them. No issues.

The molex ones are a bit dicey, as the pins tend to fall out when mating the connectors, and often don't make a secure connection. I've had at least one of those burn up. The 2-molex to 2-pcie is mostly ok for a 1080ti 8+6 pin, if the pdb is a good model with thick molex cables, and ideally, connecting each of the two molex plugs to two different molex strings. Even though I've gotten that to work for the most part, you're right to be hesitant to use that.

On the other hand, using the 8 pin EPS -> 2x pcie 8 pin, that's solid. An 8 pin EPS is connector is rated for the full power use of the 2x 8 pin pcie, and this cable has good build quality and adequate wire gauge.

Beyond one gpu per server, things get more complicated. Depending on the model supermicro PDB, some of the older ones are pretty crappy and can't handle much power draw. Even those do ok with one 250 watt GPU in my experience. The symptom of inadequate power delivery is the server will crash and usually reboot under heavy GPU load. Really easy to test for -- just fire up some crypto mining at standard power limit without overclocking. If it stays online for at least a few minutes you're probably good.
 
Last edited:

funkywizard

mmm.... bandwidth.
Jan 15, 2017
848
402
63
USA
ioflood.com
After seeing the horror stories of molex to sata cables catching on fire I've become quite skeptical of converter cables also splitting one high power cable into 2 high power cables on the same rail makes me uneasy as well. Is that cable really safe?
Also, regarding molex to sata, we had a very large number of those burn up. All the same model / manufacturer (connector had 4 dots / dimples on them). Ended up having to go through all of our servers and look for that specific model to replace with another one. They were like time bombs. Ok for like a year, then started failing regularly.

Zero problems with the replacements.
 

funkywizard

mmm.... bandwidth.
Jan 15, 2017
848
402
63
USA
ioflood.com
Also it's really dicey to replace the 4u PDBs. And the "gpu specific" PDBs are barely any better than the standard one for power delivery. Even the PDB with 8x 8 pin connectors designed to be used in a 4-gpu server, definitely will -not- power 4x 1080ti gpus, even at reduced power limit of 200w per gpu.
 

risho

New Member
Sep 3, 2019
10
1
3
I guess I'll stick with this PDB/PSU combo and just get the EPS to 2 6+2 pin cable. I don't really need to worry about any molex conversions as between the sas expander backplane and the additional sata power for powering my ssd's there are none left. I would definitely want to avoid powering my gpu using molex anyways though. tbh I wouldn't want to use molex for anything unless I absolutely had to.

For what it's worth I'm really only planning on having a single gpu in this box for the purposes of passing through to a windows vm. I haven't exactly settled on a motherboard/cpu yet, though I don't think I'll wind up picking up anythign that doesn't have ipmi, so 1 gpu should be plenty. This is all for a home server/nas/etc. This is still in somewhat of a planning stage. I currently have a gtx 1080, though I wouldn't be surprised if I wound up upgrading it to something ridiculous like a titan at some point during this server's lifecycle. Hopefully this eps to 2 6+2 will be able to handle basically any single graphics card?

Do you know if the PDB-PT846-8824 is one of the older crappy pdb's that you mentioned earlier? Will it have issues running maxed out on all rails? The psu itself is 2x PWS-1K21P-1R. I bought this server used, and these 846 psu/pdb's could be quite old at this point I imagine. Should I expect that they have degraded performance or even increased danger of use over time or should I not concern myself with that? That's another reason I'm considering just doing the atx psu mod. I have an atx psu unopened and brand new just sitting in my closet that's 1000 watts and has all of the connectors I could ever dream of and more. I don't really need the redundant psu and this is just a home build (though if i just happen to have it I won't say no).

Thanks for all of the info.
 
Last edited:

funkywizard

mmm.... bandwidth.
Jan 15, 2017
848
402
63
USA
ioflood.com
Sure, glad to help.

As a bottom line, I've not had any problem powering a single nvidia gpu off this type of configuration. Typically I use the 8 pin cpu connector with the cable previously discussed, and then I'l take the 4+4 power plug and use half of it for one cpu and half for the other. Have had no problems with this setup across a handful of different supermicro systems.

To give yourself extra headroom, it can help to power on both PSUs.

The pdb itself is not likely to fail due to age, I don't think I've ever come across that. The bad ones are just not capable of delivering a lot of power, leading to voltage sags and reboots under a heavy load of multiple GPUs.

I'm more familir with the details of the different PDBs on 2u systems, where the "826" pdb is far superior to the "825" pdb. In 4u, I've only ever seen "bad" and "less bad" options, as even the 4-gpu pdb definitely cannot power 4 gpus regardless what PSUs you install.