Linking PC PSUs for a dual rig build. - Page 1
Forum section: electronics / beginners

author: Crysis1982
author_rank: Contributor
timestamp: April 29, 2018, 09:58:05 am
content: Hey guys.I am looking to do a dual system build that will be cooled by a single custom water-cooling loop, but wanting to use three PSUs.Two main ones to run the rigs and a secondary to run two Lang D5 pumps, 16 case fans and pump/fan controlers.So what I want is when either one of the main rigs is turned on, each main PSU is linked to the PSU that is looking after the cooling loop.The PSUs will be in close proximity to each other as shown in the rear view of the case I will be using.Any help will be appreciated.

author: Rerouter
author_rank: Super Contributor
timestamp: April 29, 2018, 10:05:51 am
content: The psu on signal is switching a signal to ground, have the 5 or 12v rail switch the psu on signal of the third, with both switches in parrellel it would be either turn it onThe switch could be a relay, a mosfet with some protection, or a transistor with an appropriate base resistor.

author: Crysis1982
author_rank: Contributor
timestamp: April 29, 2018, 10:10:12 am
content: I was looking into these prebuilt PCB options. May have to do some research to link together in the configuration I am looking for.

author: Crysis1982
author_rank: Contributor
timestamp: April 29, 2018, 10:12:09 am
content: Another view of them in use.

author: Twoflower
author_rank: Frequent Contributor
timestamp: April 29, 2018, 10:27:15 am
content: Why a third PSU? Using a DPDT Relais to switch between the PSUs to power the pump.The coil is connected to a 12V rail of one of the PSU. While the N.O. is connected to +12V of the same PSU while the N.C. is connected to the +12V of the other one. The common pole goes to the 12V of the pump. The same goes for the other pole with GND. This prevents potential problems with the two GNDs of the two supplies.

author: Crysis1982
author_rank: Contributor
timestamp: April 29, 2018, 10:46:19 am
content: Quote from: Twoflower on April 29, 2018, 10:27:15 amWell I don't want to split the cooling loop. So I cant have the pumps and fans connected to just one PSU.So thought I would get a cheap $70 450w one just to run the 20 120mm fans, two pumps and fan controllers.

author: drussell
author_rank: Super Contributor
timestamp: April 29, 2018, 11:33:30 am
content: Quote from: Crysis1982 on April 29, 2018, 10:46:19 amRead what he wrote again, more carefully.His suggested setup with a relay will always run when either power supply is on. If the one which is connected to the relay coil is powered on, it will be used to power the pumps and fans. If it is NOT on, the other power supply will run the pumps and fans. If neither supply is on, the pumps and fans will not be on, obviously. Isn't that your intended behavior?

author: Twoflower
author_rank: Frequent Contributor
timestamp: April 29, 2018, 11:59:35 am
content: I should have explained the function of that circuit. But drussell did a good job to do soBut please think about to use decent PSUs for the computer(s). The cheap ones might fail without any warning signs. Sometimes taking other components with them. They are also loud and ineffective, especially if the computer idles (depending on the system that can be as low as 10W at the socket).

author: Crysis1982
author_rank: Contributor
timestamp: April 29, 2018, 01:48:31 pm
content: Quote from: drussell on April 29, 2018, 11:33:30 amI know what you are saying.I will just mean I will have to have a few redundant connections for each PSU that can only be used for the cooling system.I have worked out I need three IDE/SATA/Moles cables from each PSU (if only running two) due to the location of radiator positions and size of the case. I don't think it is going to leave me enough slots in the PSU to power the rest of the system dedicated to each PSU.This was the reason of thinking using a dedicated PSU just for the cooling might be better that's all.

author: Crysis1982
author_rank: Contributor
timestamp: April 29, 2018, 02:13:50 pm
content: Quote from: Twoflower on April 29, 2018, 11:59:35 amDont worry.I am using a 1200w Seasonic Prime Platinum at the moment.It is more the logistics as the new case will be over 1m high, 0.8m wide. I will have to use one cable for the 8 fans at the top for the PWN hub. One for the bottom for the other 8 fans. One to the middle for the two Lang D5 pumps and somehow streach it out to the digital fan/pump controller on the front.Seeing as I only have 5 peripheral slots at the back of the PSU, this only leaves me 2 to run the 4 SSHDs and 2 SSDs for the system. I dont think it will work unless I go to the trouble of getting custom length cables made up.Pick of the cabeling in my existing rig for reference.

author: Twoflower
author_rank: Frequent Contributor
timestamp: April 29, 2018, 03:08:55 pm
content: One way or the other you need to run cables 'between' the main PSUs to identify that which ones are powered. And installing a third PSU does not make the installation easier as you have less space and more cables. Especially you need to mount it somewhere in the case which has only two positions, hasn't it? But that is your decision.Nice cable management.I wonder what would require a 1.2kW PSU. My guess would be a 18 core Xeon with 3x Titan-V, 64GB Ram, 8HDDs. For the fourth GPU it's slightly exceeding the 1.2kW. Or a smaller CPU with a TDP of 90W with 4x Titan-V and few less HDDs.

author: Crysis1982
author_rank: Contributor
timestamp: April 29, 2018, 10:24:32 pm
content: Not that intense.Just a 7820X @ 4.7Ghz, two 1080Tis @ 2.1Ghz, two Lang D5 pumps, 15 120mm fans, 4 2TB SSHDs, 2 SSDs and 4 RGB strips.Plus it was 20% off at PCCG last year.

author: Eka
author_rank: Regular Contributor
timestamp: April 29, 2018, 10:58:59 pm
content: 12 VDC with non critical voltages for running the pumps and fans. Use diodes. The fans, and pumps will see 11 VDC, but will still run, but likely a bit slower. The diodes can be mounted to a plate of aluminum to heat sink them, but isolate them from the heat sink if they have cases that are live.As for connecting the grounds. Because of the isolation in the power supplies, that is a non issue unless the site has badly messed up wiring with power from two transformers going to the same outlet and don't have properly earth grounds. Even then they likely share an earth ground so it is still a non issue.My question is with the third power supply. What happens if the third power supply doesn't come on, or fails during use? Can your system automatically deal with that without cooking a CPU?Both the diode and relay methods allow the fans to continue to be powered with a power supply failure. Diodes have the advantage of being more reliable, but the disadvantage of the voltage drop. Relays can have contacts weld. Even at 12 VDC.

author: Crysis1982
author_rank: Contributor
timestamp: April 30, 2018, 12:38:32 am
content: Hopefully I will notice all the fans and pumps not working and turn off the system. There should be enough thermal headroom with the 4 480mm rads to remove the heat before I shut it down.I think I have found a solution using a pre-made PCB and PSU linking cables to make it work. It should allow the two main PSUs to jump start the third using the 24 pin. Then all I am using the peripheral connections to run miles and data cables.

author: wraper
author_rank: Unknown
timestamp: April 30, 2018, 01:10:21 am
content: Just use 2 Schottky diodes (or dual diode) at positive power rail. Thus it will be powered from whatever has higher voltage. GND is common through the case but you could put a wire for lower resistance. And WTF you would need a third PSU? Consumption is way too low to justify it.

author: Crysis1982
author_rank: Contributor
timestamp: April 30, 2018, 04:28:45 am
content: Quote from: wraper on April 30, 2018, 01:10:21 amI don't have enough peripheral ports in the back of the PSU to run everything as I would need 1.3m cables to power everything together.And I can't do it using the two PSUs as this would mean both systems would be on all the time.

author: paulca
author_rank: Super Contributor
timestamp: April 30, 2018, 07:04:59 am
content: If the cooling fails the CPU will slowly overheat, throttle and eventually HALT before damage occurs. Just like they do when your air cooler gets clogged in dust. (If you PC locks up under heavy load occasionally, this is often the cause, that or inadequate cooling).The only remote chance of cooking the CPU is if the heatsink/block comes off then the die can exceed it's failure temp before the diode temp sensor can detect the overtemp and halt the CPU.They are surprisingly hard to kill.

author: wraper
author_rank: Unknown
timestamp: April 30, 2018, 08:55:28 am
content: Quote from: Crysis1982 on April 30, 2018, 04:28:45 am, and you don't need both of them running.I did not say before but you certainly have more money than sense.

author: Crysis1982
author_rank: Contributor
timestamp: April 30, 2018, 10:27:01 am
content: Quote from: wraper on April 30, 2018, 08:55:28 amIt is not that. I don't have enough peripheral ports to run the cooling and the system due to the distance between each item. How do i make a 70cm cable go to the bottom of the case and then make its way up to the top of a 1m case.I am not doing it becase I dont think the power suply can take it, I just dont want to fork out for custom cables that are over a meter long with connections at predetermined lenghts.

author: wraper
author_rank: Unknown
timestamp: April 30, 2018, 10:45:48 am
content: If you use 3rd PSU, you still will need to make a custom cables with simple circuit. You said you will use fan/pump controller. It means you should need only very little cabling to power it from both PSUs, the rest should be powered from controller. Just use 2 molex extension cables if there is not enough length, put diodes on 12V rails and connect to power of the fan controller. Connect GND wires together and attach to the fan controller as well.

author: Crysis1982
author_rank: Contributor
timestamp: April 30, 2018, 11:01:52 am
content: Quote from: wraper on April 30, 2018, 10:45:48 amNot really. I just need to trip the third psu using the 24 pin like they do in mining rigs when using multiple PSUs.But in that configuration the all turn on.This is the cable used in the attached photo.I will just have to use two of them and wire together so the current form either main PSU turns on the third.

author: wraper
author_rank: Unknown
timestamp: April 30, 2018, 11:15:45 am
content: Quote from: Crysis1982 on April 30, 2018, 11:01:52 amIt does not work like that. If you do this, all 3 PSUs will always start altogether.

author: wraper
author_rank: Unknown
timestamp: April 30, 2018, 11:30:54 am
content: Again, you could use a simple circuit with 2 diodes to connect adapters together. BUT You will have way way messier wiring, additional PSU and 3rd power cord running into the case. If you forget to plug it, there will be no cooling. So in the end it will be very messy, unreliable and consume more power. And you still need to make a custom cable with simple circuit.While you could just take 2 molex adapter cables like on the picture and wire them together with 2 diodes. 2 in, one out, connected into the fan controller.

author: Crysis1982
author_rank: Contributor
timestamp: April 30, 2018, 11:39:09 am
content: I could just use a simple switch to isolate each main cable between these PCBs. So just throw the switch when I want to change from my workstation to the gaming rig. I have two of these ordered. It just is a simple 24 pin with a molex.I could isolate the two molex cables to a front of case switch depending on what system is going to be used at that time as I will never be running both systems at once.

author: wraper
author_rank: Unknown
timestamp: April 30, 2018, 11:44:44 am
content: I just don't understand your reasoning. You still need to modify the cables. But you are eager to put additional PSU and cause the mess. No reduction of effort, more money spent and messy result.

author: jeremy
author_rank: Super Contributor
timestamp: April 30, 2018, 11:57:13 am
content: I am going to try to help, but I’m not 100% sure that I understand the problem. It seems to me that you have two power supplies that can be switched on independently (P1 and P2). If either P1 or P2 are on, then you also want to have an extra supply P3 automatically switch on, is that correct?If so, you need to do two things. The first thing to do is to determine whether one of the supplies is on. To do this, you can make an OR gate using two diodes and any positive voltage rail on P1 and P2, kind of like the schematic in this question:https://electronics.stackexchange.com/questions/130932/switching-between-battery-and-usb-using-diode-or-logic. This is what wraper is talking about.Next, you can input this to a small circuit which will set the green wire on P3 to ground. Something like an SPDT relay as mentioned earlier would work fine, but you could also use a transistor. There is indeed a relay on that PCB you posted. For an SPDT relay, you would connect the diode or gate to the coil, connect 0V to the normally open (NO) and connect the common to the green wire on P3. Some more info on relays here:https://www.electroschematics.com/9598/spdt-relay-switch/

author: Crysis1982
author_rank: Contributor
timestamp: April 30, 2018, 12:44:16 pm
content: That is exactly what I want.Thank you for the drawings.It was either that or using a switch on the front of the case to change the circuit depending on what system I was going to be using (P1 or P2) to send the current to P3 to jump the PSU.You have been rather helpful.

author: jeremy
author_rank: Super Contributor
timestamp: April 30, 2018, 12:55:20 pm
content: Cool. Don’t forget to also join the 0V of all three supplies together (although this probably wouldn’t be necessary given they should all be earth referenced).

author: wraper
author_rank: Unknown
timestamp: April 30, 2018, 01:15:07 pm
content: Quote from: jeremy on April 30, 2018, 11:57:13 amYou either use relays with contacts attached in parallel and coil powered from 12V, or 2 diodes so current can be sinked from green wire of 3rd PSU to either of motherboards. NOT BOTH. There is no need for diodes or any other circuit if relays are used.