Dual PSU How-Tos

[ecksmen]

Ok I have now worked out the error of my ways or at least I think I have;

To recap I need to draw 1 amp from the 5 volt rail, to do this will require a 5 ohm resistor (ohms law V = I x R where V = Voltage I = Current R = Resistance).

Using the online calculator HERE also shows us this - incase my maths is fubar. (GOOGLE for OHMS LAW

So therefore I originally ordered the wrong resistor only a 2 ohm one ! I now am sourcing another resistor that should be here later on today which i will test out, hopefully this time round I will be using the correct one !

Ecks

 

[mcoleg]

what about not using a resistor at all? the default power regulation inside the psu's should take care of that.
only one of the guides mentiones the resistor. could it be it's not needed?

 

[ecksmen]

no - I dont think so. Testing the rails on the psu with it powered up with nothing plugged only gives about 11volts on the 12 volt rail and it jumps arround a lot. Even plugging in the Peltier didnt help hence the 5volt resistor mod.

Ecks

 

[thinksnow]

Unless my system is just having me on, it's stable having just done the Burning Issues mod with the two ATX extension cable-splicing. No resistors at all.

Now, if I can only figure out where to install the second PS, I'll be set.

 

[mcoleg]

ecksmen:

1, 2, or 5 Ohm, right. the question is - what wattage the resistor is rated for? if it's a serial connection, you should be getting 30+ amps on the +5 rail, right?

V*I=W, if my memory serves me well.

that would require a really massive resistor, i'd assume, to withstand that amperage.

could it be that the one you have is not rated high enough, thus the jumps in reading?

also, did you check if the ground (black) wires continue onto the casing of the psu?


thinksnow, any advise on splicing the cables?

 

[stool]

thinksnow, any advise on splicing the cables? [/B]

All of the guides have pretty good instructions for the cable splicing, and the Burning Issues one has photos to show how its done. If you go that route, try to get good quality ATX extension cables, as a couple of cheap ones I tried did not work the setup correctly.

 

[ecksmen]

With my set up I had 2 psu's one 300w and a 400w. I wanted my 400w to power my all my computer with the exception of the 9800 pro. I wanted the 300w to power the 80w peltier and the 9800 pro.

I jumpered the 300w so it would power on as soon as it is plugged into the mains supply, it would turn on but the voltages on the 12v were not stable. I then placed a 5ohm wireround resistor on the 5 volt rail to give that a dummy 1 amp load (all that my psu needed to sort out the 12v rail, different psu have different requirments, use the ohms law calculator to work out the require volt/resistance for amps.) The 12 volt stablised (11.9 - Im happy with that).

Not all psus will require you to have a load on all the rails for them to power properly, it all depends on the unit in question.

Please note I am testing the rails on the psu directly from the molex connection using a multimeter and previously had zero load on the 5volt rail. All is working fine.

I even daisy chained my second psu off the first psu using the monitor out port on the back off the first psu. This means the second psu turns on and off with the first one.

Peltier is working as it should although the 9800 wont power up off the external psu - it gives the power not connected screen on boot, maybe its a timing issue. Untill I can sort that out I will not be using the external PSU. If the external PSU fails the 9800 wont be cooled and will burn out, a risk I am unwilling to rake at this time !

Ecks

 

[thinksnow]

Say, how do you specifically power your video card? I assume that's what you meant with "9800 pro".

And mcoleg, what stool said: the guides are pretty straightforward.

Something I was wondering though, and I might re-visit my wiring if this works- has anyone spliced in their 5v line the way Baowuf mentions back on page 2?

 

[ecksmen]

Say, how do you specifically power your video card? I assume that's what you meant with "9800 pro".

And mcoleg, what stool said: the guides are pretty straighforward.

Something I was wondering though, and I might re-visit my wiring if this works- has anyone spliced in their 5v line the way Baowuf mentions back on page 2?

The 9800/9700s and some geforce fx cards have a molex harddrive/floppy style power connector on the pcb. The agp bus doesnt have enough power to feed these hungry cards so they get it straight from the psu, in the same way a CD-Rom/harddrive would. It was my intention to be able to power it from the external supply with the peltier for safety reasons.

Ecks

 

[thinksnow]

Wow! Ok, that makes sense then. I was woefully trying to picture you soldering leads onto the AGP slot.

 

[ecksmen]

Wow! Ok, that makes sense then. I was woefully trying to picture you soldering leads onto the AGP slot.

\O/ I'm a little crazy in that I often do things I shouldn't - just look at this thread, but when it comes to doing something that complicated then its not my thing. The dual power supply from my understanding can be as complicated or as easy as you want it to be. I tried to keep it simple and it worked ok - I'm going to try and get the 9800 working on it as I fail to see why it wouldnt, I also need a full tower case to put all of it in, including my watercooling.

Ecks

 

[mcoleg]

try to get good quality ATX extension cables, as a couple of cheap ones I tried did not work the setup correctly. [/B]

ehh, what are the good ones? how can one tell them apart?

 

[stool]

Cheap ones are exactly that, really cheap. Also, the wiring scheme is not the same color as a standard ATX pinout. I've gotten good ones from PCPower&Cooling and MPJA. I'd say this is a case of getting what you pay for.

 

[Como]

ERm, i hate to be a pest, but if anyone knows where a nice diagram of adding a AT psu to an ATX psu (to stabalize the 12V line AND let me get 24V for a blower) it would be greatly appreciated if you would PM me.

i also vote for stickey, unless this IS a stickey...i cant remember, i cliked on it 4 pages ago

anyways, my current Antec 400W smart power has a relatively weak 12V line, and i would like ot get that within specs. Also, i hear its not good to take half an amp of 24V from my current PSU using the 12 and -12 lines, so i'd like to get 24 using 2 psu's in a series. i dont know how to do that, nor where to mount the second PSU. i want it to automatically turn on with the ATX, i'd perferr not to pay for a relay, but i will if need be.

 

[mcoleg]

thanks for the info, stool

i was ogling this place, as a matter of fact:

http://www.stayonline.com/power_supply_cables/index.asp

servers-only store or something like that. any ideas as to the quality, has anyone bought from them? i did notice they cary some PC Power and Cooling stuff; not that's it's saying much, though.

 

[stool]

Never bought from them, but you could give them a shot. Find out how well they cover their products, and make sure the cable works fine as an extension before trying to mod it.

 

[stool]

ERm, i hate to be a pest, but if anyone knows where a nice diagram of adding a AT psu to an ATX psu (to stabalize the 12V line AND let me get 24V for a blower) it would be greatly appreciated if you would PM me.

i also vote for stickey, unless this IS a stickey...i cant remember, i cliked on it 4 pages ago

anyways, my current Antec 400W smart power has a relatively weak 12V line, and i would like ot get that within specs. Also, i hear its not good to take half an amp of 24V from my current PSU using the 12 and -12 lines, so i'd like to get 24 using 2 psu's in a series. i dont know how to do that, nor where to mount the second PSU. i want it to automatically turn on with the ATX, i'd perferr not to pay for a relay, but i will if need be.

The only way I am aware of hooking the two up is BY using a relay. Its not as if they are expensive, only cost a buck or two.

 

[mcoleg]

good point, stool...

i am still in a "wondering 'bout it" stage but i'll probably get some parts in pretty soon anyways. when i'll do, i'll post and let you all know how it worked out.

 

[demon-eater]

maybe this has been addressed but im not sure.

I have a crappy 350w and a crappy 550w power supply, what do I need to do to use both 5v and 3.3v lines from both since they equaly suck but the 12v is just fine on either? or can't I do that.

It can be permanetly cause its only for my computer and it sits on a shelf anyway without a case so im not afraid of splicing cause if it works and nobody will mess with it who cares right?

 

[thinksnow]

Question for y'all:
If MBM5 is to be believed, my SL350 has these average stats:
+3.3 = 3.26
+5.0 = 4.88
+12. = 11.65
-12. = -12.17
-5.0 = -5.11

Mind you, the only things my SL350 is running is the mobo (w/ chip & video, n'atch) and 2 optical drives.

As I've mentioned before, I did the burning issues mod so I've got a Sparkle 250 running my hard and floppy drives as well as all of my fans. I did not do the 5v splice, just the dual power-on mod.

My multimeter has settings at 10 and 50 and it's been so long since I've used one, I don't recall how to get an accurate measure but it sure looks like (on the 50 setting) the 12v is dead on 12 and (on the 10 setting) the 5v is top-dead-center on 5 when I check molex's, so I don't know what to think.

Perhaps MBM is off and needs to be calibrated (via "Kentcuky Windage") or perhaps my ATX plugs are causing a rather large drop (though they looked good before I hooked everything to the board, so who knows?)

Edit because I actually have a question to ask:
From what I've read around here, these numbers are low. I'm trying to figure out why that might be, since there is virtually no load on the Antec PS, save the mobo, and it should have plenty of power for that and a few other things!