PSUs are an expensive problem when setting up miners. They don’t directly make you money. They are expensive. You’ll probably use them until they fail, so you cant even calculate in much resale value for them. You can buy cheap desktop PSUs, but they will let you down. You can buy lower efficiency PSUs, but they don’t work out cheaper over a year of running for a multi-GPU rig. So how do you solve the problem without forking out? I’d always solved it by buying lots of lower ~750w PSUs, and just using two per rig. However even the 750w PSUs are starting to get expensive if you want gold rated ones. The pice rises effecting GPUs are also affecting PSUs, it’s just less obvious.
I’d heard before that you could use server PSUs, however it looked complicated.
Well guess what, it’s actually not complicated at all.
I was browsing ebay last week, and I spotted a listing for 4 HP 750w server PSUs DPS-750RB, gold rated, single 12v rail. The 4 of them were on buy-it-now for £60 total. That’s £15 each. Let’s take a moment to think about that. £15 for a gold rated, server grade PSU designed to run 24/7 at high load? The equivalent desktop PSU would be pushing £100, probably more. Without a great deal of thought, I bought them.
A day later they arrived. I’d seen that breakout boards existed, but they looked cheap and Chinesey, and as a man who is fairly well practised in the use of a soldering iron, I figured there was nothing a breakout board could do that I couldn’t do myself with a soldering iron.
Can I power my whole mining rig with a server PSU?
Yes, but I don’t know how. You’d need a suitable breakout board. Instead, I’m opting to only use the PSUs 12v outlet to power only the PCIE 6+2 ports. This means each rig will have a normal desktop PSU to power the mainboard, and i’ll use it’s molex connectors to power the PCIE risers. The server PSU will then connect to each GPU providing 12v only. This means I can use cheaper low wattage desktop PSUs for each mainboard, and then use the high quality server PSUs for the more demanding 12v PCIE load.
Problem 1: Making the Server PSU switch on.
So this is the first problem, how do you switch the damn thing on. With a normal ATX power supply for a desktop you just connect the green pin to a black pin and on it comes. However with these server PSUs, you just get a bunch of copper pads with no markings. Google suggested shorting out a couple of pads with a resistor. I didn’t have a resistor. I couldn’t find any explanation as to why the resistor was necessary, and some descriptions online showed them running fine with the pads just shorted with wire. I’d already googled for a pinout to explain what each pad was on the PSU, and i’d cross checked with a multimeter to make sure things matched up. Once I was sure, I soldered up the pads with a little wire, and switched it on (expecting it to go BANG). Instead the green light came on, and the fan spun up. Perfect! So, that’s how you get them to switch on.
Note: I also bought some HP HSTNS-PL18 supplies. With a wire connecting the pads to turn them on, these just go on and off constantly. However with a 470 ohm resistor connecting the terminals these do stay on correctly.
Problem 2: Attaching PCIE 6+2 wires.
This part isn’t really a problem, it’s actually pretty straightforward. The large copper pads on the PSU are the 12v live and ground pads. All I needed to do was attach PCIE connectors to them. I’ve had trouble in the past with PCIE wires melting, so I wanted to use some really high amperage, good quality wire to carry the power to the connector. I opted to use a single wire that breaks out right before the PCIE connector, rather than having lots of smaller wires. There isn’t really any purpose in lots of smaller wires if they’re all just going to terminate on the same pad, and using one thicker cable meant less solder joins that could fail, and less wires that could get tangled.
I had a bag full of old PCI 8 pin to molex connectors laying around. The quality of them was too low, so i’d never ended up using them. However the connectors themselves were just fine- so I snipped them away from the molex connectors, getting rid of as much of the thin crappy wire as possible, and soldered them instead to some 14AWG silicone wire I had. These then ran in 50cm lengths to the PSU, which they were soldered onto directly.
Problem 3: Testing.
At this point, it all seemed too easy. I decided to test it on an older R9 280X card, that I could afford to break. I plugged it in, and fired the rig up. It worked! The miner opened, and ran for an hour before I shut it off. In that time, the PSU got warm to the touch, and none of the wiring changed temperatures perceptibly. The PCIE connectors on the cards were warm- but that was inevitable, and warm is fine, as long as it’s not hot.
So next I tried it on a real production rig. I have a rig which is just the odds-and-ends graphics cards that didn’t end up in a rig of matching cards. The rig has an RX580, an RX480, and an R9 280x. I make it about 400w being pulled in this rig over the 12v rail, maybe a little less. The server PSU has now been running that rig for hours, without a hiccup. So now i’ll solder up the rest, and start using them all.
Sever PSUs work for mining. They work great. You don’t need a breakout board if you’re happy to solder and figure out the pinouts. Get the used PSUs on ebay, don’t overpay for them. Make sure you can find a pinout or an article or video about wiring up that particular PSU before you order it, unless you’re happy to be the one figuring it all out. The savings are huge- although probably less so if you’re mining on a small scale or don’t already own basic soldering equipment and a multi-meter. For a medium scale setup however I think these are a great solution.