2 Motherboards 1 PSU - Mini How-To for all you farmers out there

[stymee]

Ok, I finally got off my lazy butt and wrote this up, I hope it helps some future/current farmers out there. I have to give most of the credit to some guy named "Steve" at the no longer existing Free-DC forums where he had a rather extensive write up on this subject.

[STANDARD DISCLAIMER]Use these instructions AT YOUR OWN RISK. This worked for me, but there are no guaruntee's that this will not destroy your PSU and/or mobo! You could also endanger yourself if somethings shorts out.[/STANDARD DISCLAIMER]

The main advantage of running 2 mobo's off 1 PSU is space and heat. In my setup, here, you will see that I would have been hard pressed to fit 1 PSU per layer in that envelope.

Some may argue $$, but the PSU's I used were only $15 +shipping. I do not know if running 2 mobo's off 1 PSU uses less power than 2 mobo's/2 PSU's, but it sure feels like it should.

So here we go, How to Run 2 motherboards off one PSU the cheap/easy way, no soldering!

You will need:

(1) PSU (that you don't care too much if you kill it, in other words, DO NOT try this with your brand new PCP&C!)
(1) extra ATX power connector
(~20) gray wire nuts (16 gage?)
wire strippers
diagonal cutters
(~2) cold bud lights

1. First, you must pick a PSU for this operation. I have used cheap-O 300W Cogeden PSU's and they seem to have no trouble powering 2 M7VKQ's with Duron 1.2's.

2. This next thing to track down is an extra ATX connector with wires. Old/Dead PSU's are great for this, just cut all the wires as long as possible. I have even used old AT PSU connectors and wires, the only problem being the different color wires, it can get a little confusing.

3. Strip the ends of the wires of the extra connector and twist them up nice and neat. I like to strip about .25" when using wire nuts, just to make sure there is no bare wire showing.

4. Here's the tedious part. Now starting at Pin #1, cut the wire about 2" or 3" from the PSU. Strip each end, and twist them up with the matching wire from the extra connector using a wire nut. (Use any means necessary to make this connection, I happen to like wire nuts for their simplicity) DO NOT CUT MORE THAN 1 PSU WIRE AT A TIME!!! If you cut 2 wires of the same color, you can easily lose track of which one is which, trust me, do one at a time.

5. We will be connecting 18 of the 20 wires. The Green (PS ON) and Gray (PWR OK) will not be spliced. These wires will only be connected from the Main Mobo to the PSU. More on this later.

6. Once you're done splicing, tidy things up a bit and hopefully it'll look better than this.

I usually test the PSU with 1 mobo hooked to the "Main" connector first, just to make sure everything's peachy. Once that's proven, connect the second mobo. You will need, at a bare minimum, switches hooked up to the POWER ON jumpers for each mobo. You can connect the RESET jumpers as well, but since I don't use the RESET switches, I won't get into that.

Here is the power up sequence.

1. Turn on PSU
2. Power up "Main" mobo using the power switch. The fans for both mobo's should kick on, but only the Main mobo will boot.
3. Once the Main mobo has booted, hit the power switch on the secondary mobo, it should start to boot. You may need to hit power on the secondary mobo a second time if the first hit does nothing.
4. Once both mobo's are booted up successfully, I like do it again and check the voltages in the BIOS, I suggest you do the same.

With both mobo's running, hitting the power on the secondary mobo will turn it off, but keep the fan running. Turning on/off The secondary mobo should have no effect on the main mobo. Hitting the power button on the main mobo will power down both mobo's and shut down the PSU.

So far this setup is working great for me. I haven't put a whole lot of thought in to what is actually happening when each mobo powers up, i.e. what signals are being sent to where. I also wonder about how the whole voltage sensing situation works when the mobo's are sharing each rail. Feel free to comment and help me understand why this works, or why it shouldn't!

Good luck and Fold ON!!!!

Here are some more links of Yatta Jr.
http://forum.oc-forums.com/vb/showthread.php?s=&threadid=122568&highlight=yattamonster
http://forum.oc-forums.com/vb/showthread.php?s=&threadid=109433&highlight=yattamonster
http://forum.oc-forums.com/vb/showthread.php?s=&threadid=107333&highlight=yattamonster

 

[OSUmaxx]

Excellent writeup stymee! I hope that I have the opportunity to do this someday soon.

 

[MEMex]

Thanks for the info man! PSU are costy and this should solve man problems and keep costs low

You da man!

 

[Wommalong]

Thanks for the Info man I always thought it would be easy

 

[flixotide]

Awesome stymee... you just keep contributing with excellent material..

I hope you got Yatta Jr. back up after the probs with your client mounting.

Cheers and thanks for your contribution,

Flixotide

 

[bubba gump]

Hmm, nice guide dude.....maybe this could be stickified?

nice guide

-bubba gump

 

[Ragnarok]

Hooking up 2 mobos to one PSU is pretty spiffy. It's ingenious and cost effective too -- the overclocker way!

However. I don't think this should be sticky-fied. There are already 2 or 3 articles about this outside the forums, and I'd want to see a thread about running 2 mobos completely independent of each other on one PSU, before making it a sticky. This means no running mobo, no fans; and the ability to shut one mobo down without affecting the other one.

 

[bubba gump]

Hmm, good points....i just thought it was a good guide and it deserved teh sticky....good point

Teh Wrong,
-Bubba Gump

 

[LittlePiggie]

Hooking up 2 mobos to one PSU is pretty spiffy. It's ingenious and cost effective too -- the overclocker way!

However. I don't think this should be sticky-fied. There are already 2 or 3 articles about this outside the forums, and I'd want to see a thread about running 2 mobos completely independent of each other on one PSU, before making it a sticky. This means no running mobo, no fans; and the ability to shut one mobo down without affecting the other one.

simple:

hook the green and gray wires to rocker switches to select which mobo sent signals.

hook a three position rocker to the 12v rail to select which mobos were on. it would look like this:

| 1--2--3
| / | \
| left both right

it would take some manual labor to turn the switch, but I don't see that as being a prob.

maybe. reading back, it seems very hair brained, but hey. I tried.

for instance: when you switched to the powered off mobo would it shut the psu off? dunno.

 

[ShadowCat66]

I plan on using the info,Thanks

The switches you used for the motherboards,what rating is too low or high for that matter?I found some at Radio Shack here.Just kinda wondering which switch.



http://www.radioshack.com/category.asp?catalog_name=CTLG&category_name=CTLG_010_007_001_000&Page=1

 

[Optimum1]

Very small...

You could hardly find a switch too small --- we're talking tiny voltages to trip the power-on. Look at the itty-bitty dots they use on Dells --- soldered to a little circuit board, and no bigger than half a pinky-nail.

 

[LittlePiggie]

yeah, but that's a Dell...

 

[Daemonfly]

Slight revive here

As for the 2 independant mobos, you could use 2 double pole relays to connect/disconnect the two wires.

(just thinking off the top of my head) You would have to wire it so that whichever mobo turns on first, it would disconnect both the grey & green wires of the other mobo, and vice versa. This would need 2 double-throw relays. I plan on doing this soon so I'll probably come up with a circuit diagram (unless someone else wants to try )

 

[Wedo]

Can O' Beans,

I'd be interested in anything you can up with concerning the 2 PSU 1 mobo route. Stymee just saved me by giving me the link to this thread as I couldn't find it in the search...

There will be farming going on by the end of the month and I plan on doing this as well.

Wedo

 

[Daemonfly]

Just as an update, I think I have a circuit that will work for 2 independantly switched mobos on one PSU. One of the things I found was the power_good signal actually has a delay built into it(except cheap PSUs which can cause trouble). No delay can cause a PC to not boot up upon initial pressing of power switch button, and can also cause CMOS memory corruption in a few systems.

So I currently have a circuit with an OR gate, two AND gates & two 555 timers (one 556 chip).


With modification it could work for 3+ diskless folding rigs on one PSU, depending on power draw.

 

[bubba gump]

Whoa, i sort of understand this stuff....but sheesh, i must be a bit behind on what i need to know.......we need an electrical (concernin electricity and the like) forum here ..

 

[Daemonfly]

A "Custom Electronics" or similar forum might be good.

I was originally working torwards a simpler circuit, but then found out about the delay on the Power_ok line and figured I'd better put a delay in just in case. According to the texts I've read, theres a 0.1-0.5 second delay after power-up before that power-ok line sends the signal. Firgured I'd probably just go with ~0.3s.

When I can find the time, I'll have to bust out the prototyping board & wire up a test circuit.

 

[modenaf1]

whoa, last post 3-12?
BUMP!
AWSOME THREAD!!

maybe now people can find this faster.
Anyways, sometime in the future, i plan to do this psu mod as well. It will definatly save on the number of psu's i need, and as noted above, draw less power. I have 1 question though, in the picture, the green and the gray i didnt get, so we just let them hang in mid air or was that just to save on the complexity of the drawing? I didnt understand the "the green and gray wires should connect the main mobo and PSu only."

Cheers!
-f1

 

[bubba gump]

That means that we are not gonna connec them into the secondary ATX connector. So we just cut them out of the second connector.

The main mobo, is the one you turn on first, thats the connector where you keep the Grey and Green. Then when you go to solder the wires, don't connect the green on the "spare" connector or the gray on the spare one.

This is how I took it...yet I have yet to actually do this...

Fold and Frag on
Brian

 

[stymee]

I have 1 question though, in the picture, the green and the gray i didnt get, so we just let them hang in mid air or was that just to save on the complexity of the drawing? I didnt understand the "the green and gray wires should connect the main mobo and PSu only."

All the wires except the green and gray wires will be connected from the PSU to both mobo's. The green and gray wires will only connect from the PSU to the main mobo (the one you will turn on first). I just tape up the ends that are connected to the secondary mobo and tuck them inside some wire loom.

Hope this answers your question!

Fold On!