Wiring up the PMs for Power

Let’s delve into wiring the power for the Port Multipliers. This is probably one of the most important areas to get right or you’ll be chasing intermittent issues and you’ll have to rip apart the server which is time consuming.

In my case, I went with just a single 1200W Thermaltake Power Supply. I did this mainly because I hate cramped cases and 2 power supplies will make the case cramped and difficult to access components on the motherboard. The second reason and probably more important reason is that I already had a 1200W PS lying around!

If you do go the two Power Supply route instead, I’d recommend a 750W or larger power supply to power the Drive/PM Section. On initial spin up, these drives pull a lot of power.

Also, just make sure you get a good quality power supply – this is the one area where you want to get the best quality possible.

So in my design, the 1200W Thermaltake Power Supply has 4 main power rails, 3 of which we can tap into for power. The first power rail (black modular connectors on the power supply) is your standard peripheral power rail which consists of 4 Modular Connectors that support standard 5V/12V devices. We’ll be using this power rail to provide 5V power to the port multipliers (3 PMs per Power Supply Modular Connector) and the 12V lines will provide power for the case fans as needed.

The second power rail which we don’t have real access to is for the motherboard.

The 3rd and 4th power rails (red module connectors on the power supply) are designed to support high-end graphic cards or power hungry PCI-E cards and only supply 12V (no 5V taps available), but we have a total of 6 module connectors which is over 20 actual 12V dedicated yellow/12V wires – more than enough for a dedicated 12V run for each PM.

One of the nice things about the PCI-E Power Connectors is that they can support up to 72A at 12V (36A per RAIL). These will be perfect for providing the 12V power to the port multipliers. Here’s a chart of the max power available on each rail.

For the actual wiring on the PM side, I took standard 90 degree Molex Y connector type cable (http://www.svc.com/fc444-28.html) and cut it. Please note that you will need the 90 degree Molex connectors as the standard Molex power connectors are too large and the port multipliers won’t fit into the case if you use them.

I then took some red, yellow and black 16AWG stranded core wire and started making my cable assemblies, being careful to bundle the 5V Ground Line with the 5V/Red Cable and the 12V Ground Line with the 12V/Yellow Cable. I’m not sure if it is okay to cross the ground lines across the rails, but better safe than sorry.

When you wire up the actual PM, what you DO NOT want to do is something like this:

16AWG PS Line -> 20AWG PWR CONN on PM -> ... -> 20AWG PWR CONN

Instead you want something like this:

16AWG PS Line -> 20AWG PWR CONN ON PM
              -> 20AWG PWR CONN ON PM

The reason the second design works better is because most of the Y cables that you'll purchase will use 20AWG or even thinner wire. By having a nice thick 16AWG wire feed from the power supply, we allow the PMs to tap into a "16AWG Power Bus" versus tapping into a "20AWG Power Bus". The wire thickness may not seem like much, but in my experience it makes the difference between having 5 drives on a PM BackPlane that power up and 5 drives that don't.

When hooking up to the actual power supply, here's the basic layout of connections:

Rail 1 – Black PS Plug 1 -> 5V -> PMs 1 to 3
Rail 1 – Black PS Plug 2 -> 5V -> PMs 4 to 6
Rail 1 – Black PS Plug 3 -> 5V -> PMs 7 to 9
Rail 1 – Black PS Plug x -> 12V -> Fans in System

Rail 3 – Red PS Plug 1 -> 12V Wire 1 -> PM1
Rail 3 – Red PS Plug 1 -> 12v Wire 2 -> PM2
Rail 3 – Red PS Plug 1 -> 12v Wire 3 -> PM3

Rail 3 – Red PS Plug 2 -> 12v Wire 1 -> PM4
Rail 3 – Red PS Plug 2 -> 12v Wire 2 -> PM5

Rail 4 – Red PS Plug 5 -> 12V Wire 1 -> PM6
Rail 4 – Red PS Plug 5 -> 12V Wire 2 -> PM7
Rail 4 – Red PS Plug 5 -> 12V Wire 3 -> PM8

Rail 4 – Red PS Plug 6 -> 12v Wire 1 -> PM9

As for the actual wiring of the PMs, I crimped 4 lengths of ~30” 16AWG wire (1 yellow, 1 red, and 2 blacks) to the PM “Y-Connectors”. I then cut the modular ends off of the PCI-E/PS connectors that would typically go to the video cards and peripherals, and then crimped these wires to them per the layout above. Any unused wires were just taped off.

For all the actual crimps, I just use standard AMP style crimp connectors. Done with the right crimp tool and technique, I'd take these any day over soldering wire.

If you haven’t done it already, time to get your hands dirty!!