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A question regarding PSU's

E

Elledan

Banned
I'm currently working out the details of my soon-to-be-build cluster, and I've noticed that the PSU is actually one thing I really could afford to get rid of on each node.

Don't worry, I do see the need of having a PSU 😛 it's just that if I don't have to mount a PSU on the plate together with the other parts, I'll save a lot of space and weight and simplify the wiring of the cluster.

So basically what I have in mind is placing the PSU's at a distance from the nodes. For this I came up with two possible solutions:

- Have the necessary power cables (mainboard, FDD, HDD & CD-drive) from each PSU go to one node.

- Combine the PSU's, so that I'll basically have a 4000 W PSU if I would have 16 nodes with 16 250 W PSU's (16*250). I'll then use multiple 'power-strips', to provide the nodes with power:

Say, per 8 nodes, I'll have one power-strip. containing one (or more?) +3.3V, +5V, +12V, -12V, -5V and +5Vsb cable. When this powercable reaches a node, the necessary cables are split:

> PSU <
||
||
||== Node #1
||
||== Node #2
||

etc.

Let me know whether I sound stupid enough 😛
 
That can't be done because the moment you connect two 5V lines from different power supplies, you'll smoke em due to the fact that not every PS output EXACTLY the same voltage. Even a voltage difference of 0.1V can blow the PS. Plus, if you split the cables as you describe, you will definitely run into the issue of floating grounds and that will wreak havoc on your computers, especially if you plan to interconnect the computers (ie, ethernet)

But what you can do is stack the power supplies on top of each other, and run each set of wires to each computer.

Or you can design a 4000W power supply 🙂
 
Hmm... I should have asked this before, but how long can any of the powercables from the PSU be? More than two meters? And what is the best (read: safest) way to increase the length of these cables?
 
You can probably run the power cables up to 10ft or more and it should be fine. The longer you make it, the more the cables are susceptible to ground loop problems.

But 10-15 ft should be OK. And the best way to increase the length of the cables is to buy the same gauge wires as the ones on the PS, cut the connector off (leave some slack, maybe about 2 inches of wiring on the connector), add the extension wire, solder both ends, wrap it over with electrical tape and put some heat shrink tubing over it. Just make sure you don't get any wires of two different power supplies mixed up.


And designing a 4000W is extremely difficult and you probably won't have an outlet that'll support that much current anyways hehe. 4000W @ 112V = >35Amps of AC current. Thats going to require MASSIVE transformer and rectifying diodes, let alone filtering capacitors.
 


<< Just make sure you don't get any wires of two different power supplies mixed up. >>

Don't worry, I won't be 'playing' around with more than one PSU at a time 😉

Ah yes, the 4000 W PSU... I'll take your advice and not build one... yet 😛

Thanks for your help!
 


<<

<< Just make sure you don't get any wires of two different power supplies mixed up. >>

Don't worry, I won't be 'playing' around with more than one PSU at a time 😉

Ah yes, the 4000 W PSU... I'll take your advice and not build one... yet 😛

Thanks for your help! >>





Server and workstation power supplies are available in something like 1500W or so. You can't use the ordinary computer power supply. The voltage drop in the line between the cluster and PSU is quite significant and active compensation is a good idea. You'll need two sets of wires. One set for carrying current and another set of thin wires for feedback. A properly designed power supply will adjust the output voltage accordingly so the voltage at the CLUSTER is at specified value. There are monsters like 5V 200A, 3.3V 150A and 12V 50A sort of power supply. It requires such heavy current that it uses lugs instead of connectors.

You'll also need a dedicated 240V or 480V feed. PSU's are like 70% efficiency so at maximum load it will draw about 5700W. Power factor isn't that great and crest factor is VERY high, therefore avg. curreng will be 63A and peak current about 400A to 500A. If you don't know what I'm talking about you probably shouldn't be doing this project. Have you thought about what to do with 5700W of heat dessipated into the room? It will heat the room up quick.



 
Thank you, Jerboy 🙂

240 V is the standard voltage around here (Europe), so that's not the problem. But you're right, building such a 'monster'-PSU isn't such a bright idea =)
 
Uhm... one more question: with the wires of the mainboard-connector, every wire with the same color carries the same V and current, correct?

I know, stupid question, but I'm obsessed with safety 😛

[edit]: also, what's the best way to solder two wires together? My experience with soldering has been mostly limited to PCB's so far...
 


<< Uhm... one more question: with the wires of the mainboard-connector, every wire with the same color carries the same V and current, correct?

I know, stupid question, but I'm obsessed with safety 😛 >>



Lets address your safety concern so far:

keep this unit away from living unit.

consult your fire insurance company on coverage on fire caused by improperly desgined home brew power supply setup.


Current capability: depends on the PSU

Current draw: depends on the load(motherboard and components connected to it)

voltage: yellow=12V, orange=3.3V, red=5V, black=common ground




<<
[edit]: also, what's the best way to solder two wires together? My experience with soldering has been mostly limited to PCB's so far... >>



Depends on how you want to do it.

The below diagrams are some examples of ways you can connect wire. * means connection point.


/*\

-----*-------

| |
| |
|*|
| |
 
Thanks 🙂

Now, how strong would each way of soldering two wires be, i.e., I don't want to break the connection once I happen to accidentally pull on a wire.
 
BTW, I've got an ATX PSU on the desk in front of me, and I notice a couple of other wires as well: green, blue, grey, white and purple. What are these for?
 


<< BTW, I've got an ATX PSU on the desk in front of me, and I notice a couple of other wires as well: green, blue, grey, white and purple. What are these for? >>




White= -5V
Blue= -12V
Purple= 5V standby(always on)
green=PS on(you short this to the case and PSU comes on)
grey=P.G. ( I have no idea what this does)
 


<< Thanks 🙂

Now, how strong would each way of soldering two wires be, i.e., I don't want to break the connection once I happen to accidentally pull on a wire. >>

I would still like to get an answer on this question 🙂
 
hello, will all these systems be switched on at same time/used simultaneously .i'm sure you can allow diversity for power ,2 1500w power supplies should be enough,8 nodes per power supply
 


<< hello, will all these systems be switched on at same time/used simultaneously .i'm sure you can allow diversity for power ,2 1500w power supplies should be enough,8 nodes per power supply >>

These systems are nodes in a cluster, so yes, if possible they'll all used at the same time.

I think I'll just stick with the original PSU's, though.
 


<< soldering two wires together is strong (if not stronger than original) and reliable if you do it correctly. >>

That's what I wanted to know 🙂 Thanks!
 
You can not control the power to each computer unless you include high current relays($$$) on EACH node that is controlled by shorting or opening green wire to ground You either turn all on or off. Mobo use green wire to signal PSU to turn off.
 
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