poobah
10-16-2006, 09:02 PM
I've posted in some other forums about trying to run two power supplies in the same system without any 'good' answers.:wall: Putting aside the obvious "go buy a 600W Seasonic" for a second.. I'm curious whether there are any merits or pitfalls in running two supplies.
I see a parallel between 2 supplies and a supply with multiple rails. I imagine a rig where you have a master and a slave PS for power on purposes, with the ground wires tied together. I can't come up with a scientific reason why this would be inadvisable. I've read lots of comments like "don't do it its not safe" yadda yadda yadda. No substance, no explanation. I want to know WHY.
We do this all the time with batteries (ie, 2 12v bats serially connected is 24v, 2 12volts in parallel is 12v but twice as much current). In a naive view, its the same animal. I realize there are voltage sense issues and feedback loops, and switching power supplies can be evil, but I really can't fathom anything that a diode and couple caps won't fix. Ultimately, it's 2 DC sources with a common ground.
As to the actual usage, I conceive two scenarios:
a) the main PSU powers the motherboard, and any aux connectors (+12v on the mb, PCI-E aux, etc). PS #2 powers all drives, fans etc. The only potential connection between the two supplies is the logic boards on the drives, which *should* be isolated from the power to some point. Seems pretty safe here, though there may be some weirdness if one of the supplies fails. I'm thinking there may be some benefit here, as you have moved all the inductive loads to the slave PSU, which should allow for cleaner power on the main PSU to the motherboard and CPU. I see way more ripple on my power supplies when a hard drive goes to work than I do when running a graphic benchmark, or Prime95 :)
b) In an attempt to better split the load, you feed the PCI-E aux connectors from the 2nd supply. Although the current load is better split, I get fewer warm fuzzies from feeding the same component (video card) from 2 supplies. I'm not sure how it would react to losing power at one point or the other. Though from the cards I've looked at with aux connectors, most seem to have a fairly respectable onboard regulator setup.
Now granted, you need an appropriate case, and whatnot, and of course, you now have two potential failure points instead of 1, but electrically speaking, what's the issue? I've even recently seen 300W addon power supplies 300W FSP X3 SLI PSU (newegg) (http://www.newegg.com/Product/Product.asp?Item=N82E16817104019), almost exactly what we are discussing here! What I am missing - where's the flaw? :confused:
Thanks!
-Ken
I see a parallel between 2 supplies and a supply with multiple rails. I imagine a rig where you have a master and a slave PS for power on purposes, with the ground wires tied together. I can't come up with a scientific reason why this would be inadvisable. I've read lots of comments like "don't do it its not safe" yadda yadda yadda. No substance, no explanation. I want to know WHY.
We do this all the time with batteries (ie, 2 12v bats serially connected is 24v, 2 12volts in parallel is 12v but twice as much current). In a naive view, its the same animal. I realize there are voltage sense issues and feedback loops, and switching power supplies can be evil, but I really can't fathom anything that a diode and couple caps won't fix. Ultimately, it's 2 DC sources with a common ground.
As to the actual usage, I conceive two scenarios:
a) the main PSU powers the motherboard, and any aux connectors (+12v on the mb, PCI-E aux, etc). PS #2 powers all drives, fans etc. The only potential connection between the two supplies is the logic boards on the drives, which *should* be isolated from the power to some point. Seems pretty safe here, though there may be some weirdness if one of the supplies fails. I'm thinking there may be some benefit here, as you have moved all the inductive loads to the slave PSU, which should allow for cleaner power on the main PSU to the motherboard and CPU. I see way more ripple on my power supplies when a hard drive goes to work than I do when running a graphic benchmark, or Prime95 :)
b) In an attempt to better split the load, you feed the PCI-E aux connectors from the 2nd supply. Although the current load is better split, I get fewer warm fuzzies from feeding the same component (video card) from 2 supplies. I'm not sure how it would react to losing power at one point or the other. Though from the cards I've looked at with aux connectors, most seem to have a fairly respectable onboard regulator setup.
Now granted, you need an appropriate case, and whatnot, and of course, you now have two potential failure points instead of 1, but electrically speaking, what's the issue? I've even recently seen 300W addon power supplies 300W FSP X3 SLI PSU (newegg) (http://www.newegg.com/Product/Product.asp?Item=N82E16817104019), almost exactly what we are discussing here! What I am missing - where's the flaw? :confused:
Thanks!
-Ken