Time to catch up on some progress made in the last month - first up, wiring, starting with the PSU:
Let's start with the AC feed - this is the A/C power cable I used in my previous build: It combines the A/C wiring to Supermicro PSU, terminated in a 3-pin 0.062" Molex connector, with the power-on button and LED that is mounted to the case directly under the C14 "Kettle Plug" style socket.
Initially, this was a nice and neat solution, however, after introducing a
"bypass" flow to my main fanto support evacuating hot air from the PSU, the power-on cable has been in the way of airflow from PSU to the fan, so this time I will keep things separate to not unnecessarily obstruct heat transfer:
The A/C wiring does back into a single sleeve...
...and after crimping on a new 4-pin connector for the power on / LED button...
...I get two neatly separated cables.
Next up is this rewiring this big boy - my modded Supermicro PWS-804-1r:
For those interested in modding one for their own use (as of today, I still haven't found anything reasonably robust with more power density), have a look at
this post here where I explain the original mod. Be sure to also check
this one here explaining the upgrade to a Molex A/C connector (the AMASS connector in my first iteration sparked), and
this one here where I replace the Noctua fan by an externally controlled, more potent one in case you run into thermal issues (which would trigger a PSU shutdown). And if you scroll further back in the thread, you can see how I came up with the mod and what I broke along the way!
Anyway, as established right at the outset here, the 16AWG wiring I have chosen initially is a concerning bottleneck for the 4090's power draw and definitely a hazard.
In hindsight, it may have been the source of, or at least contributing to the thermal issues I had with this PSU initially. And, whilst at it, I also plan to swap out the 4-pin ATX plug I use to connect to the Pico PSU: It's pretty space-consuming for what it does and somewhat misplaced in an SFF system, particularly in the age of incredibly compact 12HPWR connectors - there must be something better out there...
Stripping out the PSU from its case...
...the first task is to undo the existing welds to the board without causing too much damage. Looking at this closeup you see the mess I created when I built it initially with a way-too-crude soldering iron.
Also, I have used a flux with way too much acid (I had bought it for soldering copper and happily used it for everything else)- you see how the soldering points have developed a greenish patina which is essentially a result of oxidising the metals around it - not good.
After some unsoldering and polishing, I get to presentable contacts...
...and get on to soldering on 5mm bullet connectors to 12AWG wiring which should get me about 2.5 times the cross-section of the 16AWG I have used before.
To avoid the issues I had with my last iteration of wiring up the PSU, I have upgraded my soldering gear to a Miniware TS-101 (it's ridiculously small and powerful)...
...and build a bullet holder by drilling a 5mm hole into a tile with a fireproof coating...
...to make things a bit easier when soldering.
This here is a really great guide on soldering bullet connectors onto fat cables which is not entirely banal as they tend not only to carry a lot of power...
...but also heat away from the soldering point.
With that done, I get to a first set of wires lengthened to stagger the bullet connectors in order for them to not end up on top of each other.
Apart from avoiding a bulky bunch of connectors this also reduces the risk of creating a short in case any of them isn't fully pushed in. Also, you'll note that I have two male and two female cables prepared: The male ones (exposed in a disconnected state) are the two ground terminals for CPU and GPU - no harm in them touching the case, even when the machine is on - and the female ones are for +12V. This also means that I cannot plug in the CPU or GPU the wrong way around - that would be expensive.
Next is the delicate part of the operation -
...soldering on the 12AWG wires onto the pins of the PWS-804. This requires a little planning before positioning them as I cannot afford for any of the cables to project beyond the short side of the PSU (there is absolutely no space left in the case), and the space on the underside of the PSU's PCB is severely limited - the wires have to fit into the gap between PCB and PSU case. That's also the natural limit for the cable diameter - anything bigger than 12AWG would be an unlikely fit there.
This is the outcome - four fat cables pointing towards what will be "down" in the PSU's final position.
This is different from how I had them running in previous builds: The ambition is to run all power wires along the bottom edge of the case to create fewer obstructions for airflow to the PSU. What you see next to it are Moles Nano-fit connectors...
...which I cramp onto four 18AWG wires to connect the Pico PSU.
The Micro-Fit is most amazing - it's incredibly compact and gives me the same current rating as an old-school, bulky ATX connector - and it's what the 12HPWR connectors are made from.
Here you see it compared to the one I have used for my previous iteration - that's a pretty significant space saving with no performance sacrificed.
I'll have to solder them onto the control pins of the PSU (see the post linked above for the pin-outs)...
...and as you can see here in this close-up of the de-soldered and polished contacts, I have lost a pin (PS-On - kinda key...) in the process (actually, this happened when I soldered on the previous set of wires using a way-to-crude gas soldering iron - if the iron is too hot, it will de-laminate the conductive layers from the PCB - lesson learned the hard way...).
So, what I need to do now, is to solder a wire onto this tiny bit of trace I have scratched open on the PCB with a scalpel...
...and that's where an ultra-fine tip for the TS101 comes in (did I mention already how amazing it is? Yeah...)
This should do the trick:
And that's it! Everything is where it should be!
And here is a view from the rear - it's pretty crammed so I think I have reached the limit of what I can solder onto that PSU. Also, note how different the solder points look when compared to the earlier iterations: The difference is using rosin core solder with the right type of flux being a part of the wire.
Of course, all of this wants to be tested carefully before connecting it to power - and a bunch of measurements later, I am reasonably confident to not have created any shorts over the pins (it's not entirely banal to avoid that when soldering fat wires into tiny places) and am ready to power it up -
...and: It's alive!
Next is upgrading the pico-psu to my new Nano-ATX connector.
It's a hacked part allowing me to pass through both the +5V standby power from the PSU to the board and the PS-On from the board back to the PSU to allow for proper PSU switching as per ATX standard, hence I need four wires between PSU and Pico: Ground, +12V, +5V standby and PS-On. For a guide on hacking a pico PSU into submission,
see this post from my previous build here.
This looks neat enough and should give me some flex in the wiring when connecting the parts:
...and it appears to work!
With some insulation tape applied, it goes onto the board for a test fit...
...with the Nano-Connector sitting neatly between Pico and RAM.
And just when I thought I'm done, something I have seen when unsoldering the old wires from the Pico PSU comes to mind: The +12 wire didn't look great, indeed, it looked like it had a bit too much heat. My hypothesis so far has been that all +12V terminals on the board are connected so that it would not really matter whether I feed power through the ATX connector or the separate CPU power connector - and on that basis, I have only used a single 18AWG wire to feed the Pico-PSU with +12V.
Well, if that's true, I should be able to get contact between the +12 terminals on the CPU 8-pin and those in the board's ATX connector, right? Well - my multimeter tells me: WRONG! So, it looks like ATX boards separate the +12V circuits between the main ATX plug and the CPU 8-pin, which means that my ATX/ Pico combo could pull up to 65W.
That's too much for a single 18AWG - but three, indeed, should do it:
So it looks like this little guy will need another 4-pin Nano-ATX connector fitted for two more +12 and ground wires. Unfortunately, that means I'll also need to fit four more wires to my already pretty busy PSU.
Another hour or so later I get to this...
...and an upgraded version of my PSU with two Nano-connectors coming off it.
Note how I have used them in reverse orientation to avoid confusing them: The female provides standby and control, and the male has two additional 12V/Ground pairs.
Also, comparing this to my original layout...
...here is an old photo that shows the key benefit of the smaller Nano-connectors, and bundling all power outputs at the bottom edge: A much larger open cross-section of the ventilation grid which has been previously cluttered by cables.
Should work!
Next up: Power to CPU and GPU - including a self-made ultra-low profile 12VHPWR connector!