[DIY]Cheap way to control 2 PSU in a rig

[BLife]

Hi,
 I recently ran into a situation that required to use 2 PSU in my mining rig and when the paper click trick is nice, every time I wanted to shutdown/restart the system I have to turn off/restart the second PSU manually and came across add2psu and found that to be costly so I went dumpster diving and got this solution.

Components you need.

1 Relay - SC5-S-DC-12V
1/4m  of different color Wires
2 Molex male pins
2 PCIE male pins
if you cant get the molex and PCIE pins you can use solder to solder the threads of the wire to make it single core.
4 heat shrink tubing.

The function of the relay is to connect the other circuit when the main circuit is powered up, and the connection is as follows

Connection Setup Red line indicate power flow

As you can see this relay can be powered from the first PSU that is controlled by the Motherboard and the secondary PSU can be connected to the secondary circuit of this relay to at as a switch.

Relay SC5-S-DC-12v This relay operates on 12v dc and I salvaged it from old UPS

Relay Backside It has 5 pin, 2 pins for input and 3 pins for output.

Connection of Wires Yellow & Black  wire brings in 12v from Molex and read wire and another black wire connects the pins 15 & 16 of motherboard cable.

Molex Connection Plug the yellow wire into the 12v and black into the neutral line

Motherboard Connection You can plug anyone in any slot it doesn't matter, all it matters is pins 15 & 16 must be connected.

Thats all to it, you can get a even low power relay to operate on 5v but I didn't have it.

Hope this is of some use to someone. If you have any doubts let me know.

Regards,
BLife

[joaocha]

Could you please specify the cable pinout from relay?

it is possible to make 2 slaves psus?

[fanatic26]

If one of the PSUs is just powering video cards you do not need to reset it when you reset the PSU powering the board.

[JaredKaragen]

FYI, the best way to link two PSU is to simply connect the PS_ON line (I believe grey?) between both PSU's.  They will both get the power-on line pulled low at the same time... so it should fix the rebooting/power off issues.

For issues with the PSU not turning on fast enough;  just be sure the PSU with the slower switch-on time is connected to the mainboard of the PC motherboard (if using in that config).

If one of the PSUs is just powering video cards you do not need to reset it when you reset the PSU powering the board.

This is also correct.  The +12V will not backfeed into the mainboard keeping it on or causing ghosts;  the PSIE power plugs pretty much only feed the CPU die and the memory directly (for the most part).

[BLife]

If one of the PSUs is just powering video cards you do not need to reset it when you reset the PSU powering the board.

Thats true, but at my place Internet goes down at random times and I have a Orange Pi shutting down the system when that happens so, control of the second PSU is needed in my case unfortunately.

FYI, the best way to link two PSU is to simply connect the PS_ON line (I believe grey?) between both PSU's.  They will both get the power-on line pulled low at the same time... so it should fix the rebooting/power off issues.

For issues with the PSU not turning on fast enough;  just be sure the PSU with the slower switch-on time is connected to the mainboard of the PC motherboard (if using in that config).

I always like to keep the circuits isolated as much as possible(paranoid maybe) thats is one of the reason I went for this setup.

Could you please specify the cable pinout from relay?

it is possible to make 2 slaves psus?

The pin out is as follows

4------5
|        |
2--3--1

Pins 1 & 2 is the main circuit and pins 3,4 & 5 is the secondary circuit

when there is no power between pin 1 & 2, pin 3 is connected to pin 5, but when there is power between pin 1 & 2, pin 3 is connected to pin 4

So connect pin 1 & 2 to the main PSU's 12V & neutral and pin 3 & 4 to pin 15 & 16 of the secondary PSU.

To answer your second question, yes you can but I wouldn't recommend, I like to keep the circuits isolated as much as possible, as adding the third psu is simple, repeat the above and you can control it.

Hope this helps

Regards,
BLife

[JaredKaragen]

I always like to keep the circuits isolated as much as possible(paranoid maybe) thats is one of the reason I went for this setup.
BLife

It's just a pull to ground;  no chance of any "crosstalk".

In fact, there are dual psu adaptors that specifically do what I mentioned and have been widely used for many years.

But the relay also works as well, I just see as jumper pin being the cheapest and simplest overall =)

[fanatic26]

Thats true, but at my place Internet goes down at random times and I have a Orange Pi shutting down the system when that happens so, control of the second PSU is needed in my case unfortunately.

Cant you just program the GPIO pins on the RPi to control the PSUs as well then?

[Elder III]

I applaud the creativity and effort put into it, but an add2psu for $19 or less may be cheaper then getting those materials together, not to mention the time factor.

[JaredKaragen]

Thats true, but at my place Internet goes down at random times and I have a Orange Pi shutting down the system when that happens so, control of the second PSU is needed in my case unfortunately.

Cant you just program the GPIO pins on the RPi to control the PSUs as well then?

Yeah, buts it's always smart to use a transistor as a gate when it comes to controlling TTL logic.  Be sure to include pullup/pulldown resistors, and add a cap if you need soft-off situations.

[BLife]

It's just a pull to ground;  no chance of any "crosstalk".

In fact, there are dual psu adaptors that specifically do what I mentioned and have been widely used for many years.

But the relay also works as well, I just see as jumper pin being the cheapest and simplest overall =)

+1 on the bold part, but shutting it down will be a problem though. To be honest with you I was not sure about the "crosstalk" so was the reason I went with this setup. Thanks for educating me. I really appreciate that.

I applaud the creativity and effort put into it, but an add2psu for $19 or less may be cheaper then getting those materials together, not to mention the time factor.

 To be honest, if you have a dead PSU lying around then you can build this setup for free in less than 5 minutes. Even if you purchase all the components it wont cost more than $2

Regards,
BLife

[JaredKaragen]

+1 on the bold part, but shutting it down will be a problem though. To be honest with you I was not sure about the "crosstalk" so was the reason I went with this setup. Thanks for educating me. I really appreciate that.

only if you want that PSU to be controlled/shut off independent of the first... Otherwise sharing PS_ON they work in unison

the PS_ON line gets pulled to ground by the motherboard when you tap the power button (in most cases) and will have a ~1.2k pullup resistor or something thereabouts.  Just enough to float the pin high always... same on the psu if im not mistaken.  this is where they can technically "share juice"... in a manner of speaking, but the high resistance pullup negates any bad things from happening... and on the MB this condition is also present  and you will probably be able to see the pullup voltage. (measurable via multimeter most likely)   The PSU, possibly not because I would see it being a voltage reference crossover, and being on the negative side, you have no reference + tap to test without opening the PSU

Glad to have helped though =)  I just don't want to see you with more possible points of failure (relays can really suck ass sometimes).

[BLife]

the PS_ON line gets pulled to ground by the motherboard when you tap the power button (in most cases) and will have a ~1.2k pullup resistor or something thereabouts.  Just enough to float the pin high always... same on the psu if im not mistaken.  this is where they can technically "share juice"... in a manner of speaking, but the high resistance pullup negates any bad things from happening... and on the MB this condition is also present  and you will probably be able to see the pullup voltage. (measurable via multimeter most likely)   The PSU, possibly not because I would see it being a voltage reference crossover, and being on the negative side, you have no reference + tap to test without opening the PSU

Glad to have helped though =)  I just don't want to see you with more possible points of failure (relays can really suck ass sometimes).

 Thank you for taking the time to explain it in detail, I hope this helps someone/anyone save some money with 2 or more psu setup.

Regards,
BLife

[devlin]

As far as I know is not recommended to use a relay directly connected to PSU, can damage motherboard or other components (voltage spike because of inductive load). At least use a flyback diode.

[JaredKaragen]

As far as I know is not recommended to use a relay directly connected to PSU, can damage motherboard or other components (voltage spike because of inductive load). At least use a flyback diode.

schottkey diode*

[lautre]

i have a little rig with 2 underclocked(for the core) and undervolted 480 that is using 2 psu but it have destroyed 3 PSU  in 2 weeks (old psu's found on used computers)... not sure why... but something is strange, i have one PSU for the MB+one GPU& riser and the other PSU is for the other GPU+Riser (i have bridged the green and black cables to get the psu running). And if i turn off the Main PSU the CPU fan is still moving so it get electricity from the 2ND PSU via the USB cable plugged on the pcie 2x.. !