Other 2 PCs 1 Bulgin?

[Kmpkt]

Hey Guys,

Quick question that is basically summarized in the title of the thread. Can I double wire a bulgin switch to start two PCs simultaneously. I'd only need to double up on the + and - for the switch for the on/off functionality. Everything else (LED power etc) could go to a single motherboard without issue.

The reason I am asking this question is that I would like to do an STX build where I have one HDPlex 80 ACDC powering the STX with a 6700T (switch connection one), while the second switch would go to a BPlus SWEX to manage power through an HDPlex 160 to power a GPU.

 

[BirdofPrey]

It's possible, but I wouldn't recommend it.

The most obvious issue would be if one system doesn't switch on for some reason or another, which while likely rare if wired properly, is possible, but more than that, since the motherboards can power themselves on and off at will, you may run into a situation where one board is on and the other is off, a a single switch won't be able to power just one board on or off unless you had a second connected to it that made the power signal go to only one board.

 

[Kmpkt]

What is the drawback to having one PC on while the other is off? The only obvious one I can see is the inconvenience of having to shut down the one that is on and try again. Also in the application I am planning to use this for, the second "PC" is just a SWEX and a GPU, so there really isn't a PC on. In the case that the STX turns on and the GPU for some reason doesn't, I'd simply get a boot without a dGPU. Pretty sure that if the GPU circuit received power and the STX one didn't, nothing would happen as there would be no signal from the PCIe to the GPU to actually spin up. Is this correct?

 

[BirdofPrey]

What is the drawback to having one PC on while the other is off? The only obvious one I can see is the inconvenience of having to shut down the one that is on and try again.

That is the issue exactly. not insurmountable, but it could be annoying.

Also in the application I am planning to use this for, the second "PC" is just a SWEX and a GPU, so there really isn't a PC on. In the case that the STX turns on and the GPU for some reason doesn't, I'd simply get a boot without a dGPU. Pretty sure that if the GPU circuit received power and the STX one didn't, nothing would happen as there would be no signal from the PCIe to the GPU to actually spin up. Is this correct?

Ah I might have misread what you were trying to say. I thought you were going to use more than one actual computer, not that the second was actually just a switch for a PSU.
Assuming the GPU is to spec (which I tend to be suspicious of) it should remain off until the motherboard signals it to turn on, but at the same time, I'm not sure how that works when you are connecting through an M.2 slot (as STX has no PCIe slots).

Again, it should work, but I always leave room for debugging even if it's a separate switch hidden under the case panel.

I bet @QinX would know exactly what to do

 

[jeshikat]

The motherboard power switch header actually puts out 3.3V on the positive pin as long as the PSU is giving it Standby 5V. When you press the power switch it just shorts the two pins together, pulling the voltage down, which tells the motherboard to turn on.

This is why you can turn motherboards on by using a screwdriver or other conductive object and touch the power switch pins together to turn it on if you're doing quick testing and don't have a power switch handy.

So I'm not sure what kind of issues you'd run into with two boards on one switch.

That said, I don't think it's necessary to have the PSU turn on and off for the GPU. PCIe has 3.3V for standby power anyway so in a normal computer it's not completely powered off when the computer is off but the PSU is still plugged in anyway.

 

[Kmpkt]

So if I had HDPlex 160 AC-DC to say HDPlex 160 with a modified 4pin EPS to 8pin PCIe cable being the only thing coming out of it, once the GPU got the signal to turn on through the PCI BUS, the power would just flow? This would obviously be a really nice solution if this is how it works.

 

[jeshikat]

It should. That's what I found here: https://smallformfactor.net/forum/t...-with-thunder3-pcie-box.913/page-2#post-17816

I'll be receiving my EVGA GTX 1060 SC in a day or two so I'll have an additional data point besides just the GTX 980.

Generally parts pull power from the PSU, the PSU doesn't push power to the parts. That's why using a 120W AC adapter on a laptop that normally only needs a 65W adapter doesn't just immediately fry it.

 

[Kmpkt]

Awesome, thanks for the info. I'll likely try running that configuration when I get all my parts then.

 

[iFreilicht]

Just as an additional piece of information, there are so called double pole buttons and switches. Those have two isolated switches inside, so you could do precisely what you asked. You can search for DPST, DPDT and DPCO to find those.

 

[Kmpkt]

Would this work?

http://canada.newark.com/schurter/1...id||kword||match|&CAWELAID=120185770000802904

 

[BirdofPrey]

You need a normally open switch rather than a toggle (on/off)

 

[Kmpkt]

http://canada.newark.com/itw-switches/76-5910b/vandal-resistant-switch-76-59/dp/15J9172

???

 

[iFreilicht]

Yup, that seems about right. The datasheet is a little vague, though.

 

[CC Ricers]

Since anti-vandal switches for turning on PCs tend to be momentary, that makes them single-throw switches as there is only one possible connection to make. If a momentary switch were wired to short pins for two separate devices, that would be a double-pole, single-throw. And on the contrary, a toggle switch that is wired to short pins for one device or another, but not both at once, is considered a single-pole, double-throw. For future reference here's an article some further info on structure of switches that can help you out.

 

[iFreilicht]

Momentary switches can be double-pole as well. You just wouldn't wire the NC pol to anything in our scenario.

 

[QinX]

That said, I don't think it's necessary to have the PSU turn on and off for the GPU. PCIe has 3.3V for standby power anyway so in a normal computer it's not completely powered off when the computer is off but the PSU is still plugged in anyway.

I'm not totally sure as well, but I believe my Palit GTX970 turns on the fans when power is applied to it. But that also might be an isolated case.
I could try and jump my HDPlex with the R9 Nano and see if it turns on the fan?

I've had good succes with a simple transistor that shorts the second PSU to Ground and is switched using 5V from the first PSU. I could make a PCB for that, although I just soldered mine inline with the cable, similar to how you'd use a resistor/diode inline with a fan to drop the voltage.