using 2 psus to power different rails

[binkgle]

my comp has an enermax 420w psu, which has very good ampage on the3.3 and 5 volt rail, but only 15 amps on 12v1 and 14 on 12v2. for my sys, that's not really enough.

i have a spare400w psu from powmax with less power on the 3.3 and 5 volt rails, but 25mps on the 12 v rail. now that's more like it. how could I use my enemax for the 5 and 3.3 rails, and mypowmax for my 12v rail? is this possible? what parts get power from 12v, apart from cpu? i am willing to run the case without its side panel on if necessary (i use an antec superlanboy case).

edit: just realized... would my enermax having 15 amps on one 12v rail and 14 on the other mean that it actually has a 29 amp 12v rail? if so... i'm home free.

 

[BillR]

my comp has an enermax 420w psu, which has very good ampage on the3.3 and 5 volt rail, but only 15 amps on 12v1 and 14 on 12v2. for my sys, that's not really enough.

i have a spare400w psu from powmax with less power on the 3.3 and 5 volt rails, but 25mps on the 12 v rail. now that's more like it. how could I use my enemax for the 5 and 3.3 rails, and mypowmax for my 12v rail? is this possible? what parts get power from 12v, apart from cpu? i am willing to run the case without its side panel on if necessary (i use an antec superlanboy case).

edit: just realized... would my enermax having 15 amps on one 12v rail and 14 on the other mean that it actually has a 29 amp 12v rail? if so... i'm home free.

Everything else being equal and assuming you did the proper calculations:

http://takaman.jp/D/index.html?english

And, further assuming your temps stay within reason you would appear to be home free.

You can hook two, or more, PSU’s in parallel but it can quickly become complex when your dealing with varied specs. One of the big issues would be (god forbid) a “Ground loop” issue, where by accident or through a bad connection you create a second ground. Computers don’t tolerate that sort of thing very well.

Luck

 

[Ice Czar]

I agree with BillR
But I have run dual PSU before

cut and paste 101
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synch 2 PSU each as a seperate bus

1. Hardwired
2. With a relay

or employing a shared bus Like a redundant PSU

1. with resistors
2. with mosfets
3. with diodes (Single Source Fault Tolerant Power Systems)

(3 is slightly outdated now see gee's post > http://hardforum.com/showthread.php?t=776885)

I ran 2 hardwired 400 watts and a large RAID array for 3 years without issue on one of my boards (Abit KR7A)
however it may have been a contributing factor in the death of another board (ECS whatever )
though Im not at all sure about that

not running them synchd however certainly corrupted the hell out of the array
eventually switched to a Zippy Emacs MR3-6450P N+1
with considerably less total wattage but plenty for what was actually required
with 32A on the +12V rail for the drives and considering the mobo's VRM was powered off the +5V
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regarding "proper" calculations you might find the realworld section of this applicable
there are numerous examples of that Ive run here on the board, but Im a bit pressed for time this morning

cut and paste 202
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Do the math here: http://www.jscustompcs.com/power_supply/
There's a good chance you will need a bigger PSU than the 470..

And once again. Let's not forget that these calculators are absolute worst case.

well as far as calculators goes, that one sucks (sorry)
its very important to actually determine the amps per rail
and not all calculators are automatically the worse case senerio
I use > takaman's Power Supply Calaculator v2
which does have the option to set a utilization percentage, and to manually enter amp values for a given component
which is very handy if you have real world test values like
Power Consumption of Contemporary Graphics Accelerators: ATi
Power Consumption of Contemporary Graphics Accelerators: Nvidia
(all the better because they break out the draw between the AGP and the auxillary connector, which on an ATX12V v2.0 is on different +12V rails)
and various databases like Processor Electrical Specifications
(if the board has a +12V auxillary you add to the +12V otherwise it goes on the +5V rail,
and you convert the watts to amps for the appropriate rail, AMPS = Watts / Voltage)
or the actual spec sheets on the components (like say from Seagate)

that way Im able to run multiple calculations
first I do a "full" calculation, of all the additive maximums of the components
then for an ATX12V v2.0 supply or an EPS12V supply I repeat that for the +12V1, +12V2 and additionaly for EPS12V +12V3\+12V4 rails

then I run a "realworld" worse case senerio,
Its just as likely Im helping someone calculate a NAS as a lean gaming rig
so a "spinup" calculation is the first criteria
all the fans and HDDs\RAID arrays at 100% value and a 25% value for the CPU\GPU, often that will tell me if a more powerful supply is needed simply to boot or if the NAS\SAN need to employ a controller with a delayed spinup option
(common on SCSI controllers, and found on quite a few ATA)
once the fans and HDDs are spinning they will drop to 1\4 of their full rating, so I recalculate with that value as a static load, and throw in a 100% CPU\GPU and single optical (full spinup draw) for a worse case senerio realworld


Interpreting the veracity of a manufacturer is the tricky part
since we dont get to actually see the engineering test specs
which will typically say sometghing like
rated for full power at 25C decreasing linearly to no power at 70C
and your operating temperature being around 40C

generally I start with deducting a third off the rated amps for temperature
and then start to match to the baselines, factor in thermal considerations (PSU placement, type of thermal solution for the rig,) and special factors like overclocking or usage patterns (NAS\Server\Workstation\word processor ),

when I actually make recommendations however I typical build in a healthier safety value than the "real world" worse case senerio unless someone has specifically stated they are running a UPS
------------------------------------------------------------------------------
all the above in the event someone actually employs the search feature
squirrel away the linkage in the event you need to run a TEC\Peltier and or big pump
Id recommend a Relay in that event

then run the calculations for each of your +12V rails
will give you a good idea of what kind of room you have for upgrades on that supply

+12V1 will be mobo, CPU, PCI Cards, fans attached to the mobo and AGP slot (24 pin main & 4 pin Aux mobo connector)

+12V2 will be Drives, Case fans, lights, pumps, and Auxillary Power to the Video Card (all other connectors)

 

[binkgle]

way way too comlicated and risky. seeing as my enermax has 2 12v v rails, one with 15, the other with 14, would that mean it is the equivalent of a 29 amp single 12v rail psu? if so, i won't be doing any modding (probably won't anyway)

 

[Ice Czar]

seeing as my enermax has 2 12v v rails, one with 15, the other with 14, would that mean it is the equivalent of a 29 amp single 12v rail psu?

no it means that each rail needs to be calculated seperately.

+12V1 will be mobo, CPU, PCI Cards, fans attached to the mobo and AGP slot (24 pin main & 4 pin Aux mobo connector)

+12V2 will be Drives, Case fans, lights, pumps, and Auxillary Power to the Video Card (all other connectors)

so lets say you have 10A of draw with the components on the +12V1,
it means that the extra 5A is simply unavailable to any of the components on the other rail

its entirely possible to run out of capacity on one of the rails
and yet have excess power available on the other

it depends on what your trying to power

you should use 10A and 9.3A respectively for the amp ratings of that supply

 

[Ice Czar]

http://www.xbitlabs.com/misc/picture/?src=/images/video/ati-vs-nv-power/6800_table-b.gif&1=1
used the 375/900 figures and awarded you 2 x 120mm 2300 case fans (0.25A per 6W total)

Theoretical maximum
http://takaman.jp/D/?M=PbQDQbd@hSASgT4UAkG5@IDTHYZAZavHEMZ&english
+3.3V @ 3.5
+5V @ 9.6
+12V @ 18.1
Totals Watts 287W (w\ a PSU at 25C)

+12V1 @ 8.5A
+12V2 @ 8A

worse case senerio
w\ the CPU GPU mobo HSF at 100%, an Optical drive at full Sinup (100%)
HDD and case fans @ 25%

+12V1 @ 8.16A
+12V2 @ 5.3A
+12V Total 13.46A

so the supply comes out like this
.......................25C.......................40C
+12V1..............15A......................10A
+12V2..............14A......................9.3A

and that gives you
...............needed................supply..............safety margin @ 40C
+12V1.......8.16A..................10A..................1.84
+12V2.......5.3A....................9.3A.................4A

so your good to go and for instance have room for a few HDDs on +12V2
or a PCI card or two (depending on if it needs much +12V) on +12V1