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How to run 3 crackrack boards on one power supply

Ah - Great one... 🙂

I want to run ATX - A7V's with Durons oc'd to 900.
I heard you have the plans for running multiple boards off one PS. I'd be real interested if you still have those. 🙂
 
Not really plans. I opened the power supply, knew the current limitations of the supply and figured how many AT machines it would run.

For you, you would probably want to get some form of 100 watt power supply (ATX) and see if you can power the boards with that. If it looks fine for your needs, then follow the following. 🙂

Get a 300 Watt ATX power supply. You going to need to do some shopping, but for now, we just want to look at the PCB (PC Board) in the power supply. Look at the wires going in. Now I'm a little rusty with my ATX pin out off the top of my head so these could be wrong, but I believe they are correct.

Note, I know this is right, I double checked

This would be the side with out the locking tab

Pin Signal
1 3.3vdc
2 3.3vdc
3 Ground
4 5vdc
5 Ground
6 5vdc
7 Ground
8 Power Good (5v if good)
9 5v sb(This wire might not go to the standard 5vdc plane
10 12vdc

Other side starting back near pine 1 (orange wires)
11 3.3vdc
12 -12vdc
13 Ground
14 On/Off Control (short this with ground to power on ATX power supplies when no MoBo is connected. Very handy to see what blew up when a machine died

15 Ground
16 Ground
17 Ground
18 -5vdc
19 5vdc
20 5vdc

OK, now here is the fun part. You can see that you have alot of the same wires going to different pins. Now if you have 3 power supplies that's 60 wires. There is no way in heck you will be able to put 60 wires into that PCB. So, you are going to have to do some soldering.

Get some solid copper wire, of the same diameter as the hole on the PCB board. Not sure what gauge off the top of my head, but this is pretty heavy stuff. Now, MAKE SURE if this copper has insulation on it to scrape it off. (A thin film of plastic that you can't see, but it will scrape off with a knife). Take about a 1 inch part and take off all of the insulation. Then bend one end into a P so that the loop part is big enought for you to put plenty of wires through it.

This is where it gets fun. You going to need some parts. If you go to this link for Jameco you will see that they have ATX connector parts. You need the pins (147395) and the connector (147387) to do this. You might want to get the crimper (99442), but it is not needed. I would actually buy the parts, and do it with a pair of pliers. If you feel you need the crimper, buy one locally so you can return it if you decide it's not much better. 🙂

Now that you have the parts, you will need wire. Try to find some of the same gauge as the existing power supply wires. (20 gauge???)

Ok, now you figure out the lengths of wire you need. Add 5 inches, and start cutting the 60 lengths. Then strip about 1/2 inch of insulation off of one end, and about 3/4 inch off of the other end on each wire. Crimp/plier on the pins to the 1/2 inch end, and then tin it with solder for a solid electrical connection. Then whey you have 3 set's of these done, take the wires, and match up all the common styles. 5 volts with 5volts, grounds with grounds, and special signal wires with themselves. (You will always get about 3 bundles of 3 wires, don't try matching power good with the 5 volt line to save time, it won't work).

Anyway, once you have them matched up, take the solid copper P figure, and start adding wires to it. To do this, just make a V at the end of the wire, hook it onto the copper P, then mash the wire closed around the V, and solder. (You can either solder them on one at a time, or all at once. I did the all at once, and found it to be easier) Having another set of hands comes in handy here.

Once you have a group of wires hooked into the P, go to the nice power supply you have, and start removing all of the leads that go to internal computer connections. (FDD and HDD power lines also, maybe leave one or two on if you need, but you might be putting your power supply at risk). Once the wires are pulled out, you will see the board is labeled with their locations. If not, well, maybe we should have written them down first. 🙂 (I figure your going to read this all the way through at least once). Take the P figure you have and stick the | into the power supply hole. Try to arrange it so that the P won't be too near other P connectiors. (Now if you have either black electrical tape, or heat shrink, cut a bit off and put it onto the P/wires. Put the end into the board, and put it down pretty close to the board. Solder in the connection with a clean amount of solder. then get the heat gun and shrink your heat shrink, or get your tape out and cover the P and all the exposed wires cleanly. 🙂

Repeat until done. 🙂

Now pull out your multi meter and power on the power supplies. (Neat Note. Now that you have modded 3 connections into one power supply, only one power switch needs to be connected to a machine to power it on. This means that you can only short one of the power on/off wires to ground to turn on this supply). If any smoke comes out go back to start and look at your wires. If everything looks ok, start testing the voltages out. Again power good should be around 5 volts. You can assume that if it's with in 1 volt of the 12 and 5 volt lines your fine, and about 1/2 a volt for the 3.3 vdc lines. Check all the pins, then check again, then get someone else to check the last time. This is because if your wrong here you could end up loosing some good hardware. Now for the faith part. You might want to get some POS board, and hook them up to the supply. Once this is done, power it on and see if all 3 boards post and turn on correctly. If one doesn't turn on or they all don't turn on, double check the pins again on the multi meter. If two turn on, and one doesn't, try disconnecting the one that didn't power on and see if the others power on ok. Or, try disconnecting the one that powered on, and see if the no post powers on ok.

The reason for all of this, is to make sure, the power supply really has enough juice to power the boards. You could be brown outing, or you could have one wire off. (trust me, it's a pain in the butt to fix if you do have one wire off.)

Repeat until done with desire to mod power supplies.

It takes time, and isn't always easy, and you should keep at least one power supply handy incase one fails. If it fails, it's just a mater of pulling out all the P's in the bad one, and connecting them up to a new board.

Man, this is a long post.

Any Questions?

LD
 
Thanks LD...
I'll have to go over this in detail. I appreciate the time it took to write! 🙂
 
Thanks LD! I was contemplating how to do this.

DanC, could you change the thread title so it is more descriptive?
I may be wanting to hunt this down later. Thanks.
 
Could you just get one of those ATX extentions, cut the female end off and then cut your power supply wires and just crimp them all together with buttsplices (or you could solder them too)?

So it looked like this

. . . . . . . . . . . . . . . . .___________________
ATX PS ------[SPLICE]{
. . . . . . . . . . . . . . . . .\__________________
 
That's what I was wondering about. It certainly is an elegant way to do it, but I'm looking for the easiest way. LD - do you see a reason you couldn't just do it from the wire end?
 
The current load on the original power supply wires is too great. It can heat up and cause the insulation to melt. Not a pretty picture. Plus, with more splits there can be trouble at each split. The back plane for each voltage, is properly shielded on the board, so you get less noise and that can make a difference.

As for the copper vs the stranded. Stranded won't hold a shape as well, and it can't handle as much current. (Solid copper isn't going to melt or heat up) Stranded, if you have current going through a loose strand, it can heat up/move (Trust me, it's not fun). The other reason (the better of the two) is because it takes one little strand to short two voltage planes together and once that happens, there is a good chance on loosing all boards connected to the power supply

LD
 
OH Man, DanC tell me if it worked for you. </ before I put my hardware at risk! :Q

Nice tutorial LD. Thanks 😀

I believe I'd just go with two mobos per PS myself, but to each they're own.
 
I think you could run two &quot;Rack&quot; single CPU mobos off a 250w PS.

I'm currently running Dual Celeron &quot;Rack&quot; boards off a 145w PS with no problem.
 
Yeah, it's just going into 3 way that you hit problems. The reason I did this, was that spliters would cost about 20 bucks each, this just cost me a little time, and Brad's hands. 🙂

LD
 
Just to let you know the average computer (not including monitor) uses around 65Watts of power. In a crack rack setting it obviously would be less due to the lack of components attached. I can find the URL info supporting this claim if anyone needs it.

Now this does not say the wire used to power parts of the board can be used split the way you are wanting to do it, but you can be assured that with a 260Watt PS the wires are able to handle at least 2 boards.🙂 I wouldn't hesitate hooking up 3 personally.
 


<< The current load on the original power supply wires is too great. It can heat up and cause the insulation to melt. >>


Not to be argumentative, but if the wires/connectors were shipped with the PS wouldn't they also figure into the PS rating too?
How could someone sell a 300W PS and have wires that could only handle 200W?
I realize that it might be pushing the envelope a bit, but it's seems like it should work.
 
You are right to some extent. The 5 volt and the 12 volt leads that go to hard drives and floppy drives and more crap..... Well, that's no longer there. That is the main usage of power on a power supply. So now you have the same amount of power going through less wires.

That's the problem you face. Again, you won't hammer current if your carefull, but I had a 200 watt power supply (mis-labeled with a sticker over the main label) and with 4 boards, the wires got hot. This is why I say, from experiance, don't try to push the wires that come with it. Remember, power supply builders will do whatever it takes to cut the cost of the supply down, so going to a lower gauge wire will save them thousands of dollars.

LD
 
LD you are correct, a 200W supply would be over-extended with 4 boards (65W X 4 = 260W). I said I wouldn't hesitate to hook up 3 on a 260W PS.
 
Yeah, I run 4 machines off of a 250, now these are AT socket 7 machines, so it's not to big. I don't want to scare people, I just want them to understand, that you want to have a little bit of safety margine. 🙂

Anyway. The feed back is good, because this can soon be a cluster link, and we will have as many questions answered off of this page.

LD
 
i didnt think it was worth the hassle to
run more than one atx motherboard off of one p/s.

i payed like $11 each for 250 watt p/s for my crack rack.
and that is with temp controlled fan.

 
DanC, since you are going to attemp this, will you care to document it and take some pics for us 🙂
 
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