Sign in with
Sign up | Sign in
Your question
Closed

Can i run 2 identical power supplies as one?

Last response: in Components
Share
January 29, 2011 3:46:05 AM

i have two 500 watt power supplies of the same make same model, i was wondering if there is any way to run them both and have 1000 watt output, i have done some research but all i have come up with is this

http://www.frozencpu.com/products/5637/cpa-167/Lian_Li_Dual_Power_Supply_Adapter_Cable.html?tl=g11c28s91

From what i have seen most people use different power supplies and the problem there is that they wont run at similar power.

The reason i am asking is that my computer uses quite a bit of power and makes some components such as the dvd drive not work, for example while i am burning it the drive does not get constant power and either pauses or fails to burn at certain speeds.
a c 246 ) Power supply
January 29, 2011 6:03:56 AM

Its not a good idea to do it off of two units, you would need to pay very careful attention to your load ballancing to make sure you dont crossload a unit too heavily, its generally much easier and safer just to get a single better unit that can handle your system just fine. I definitely recommend against trying to rig two units to run as one, it can be done but its not suggested.
January 29, 2011 6:08:21 AM

I wouldn't do it!
Related resources
January 29, 2011 1:42:06 PM

That adapter you linked won't run them "together" into a single 1000w supply. It will just allow you to run two power supplies and have them both turn on together. For example, you use one power supply to power your motherboard and hard drives, and a second one to power your video card or cards. They'll still be seperate technically.
January 29, 2011 6:28:12 PM

alright thanks for all the replies i think i will just run a second power supply for my dvd drives and extra fans.
January 29, 2011 9:18:05 PM

Running a second power supply for your DVD drives and fans is a bit of a waste. Usually you run one heavy load on each power supply....

e.g. motherboard on one, several hard drives on the other
e.g. motherboard on one, vid card and hard drives on the other
e.g. motherboard and drives on one, video cards on other.


a c 144 ) Power supply
January 29, 2011 11:56:54 PM

If you are going to run 2 PSU's in one system, use one of them to power your video card. Fans represent an insignificant load.
January 30, 2011 12:26:16 AM

yea you can run 2 in one system but i would really try to stay away from this setup as much as possible, you might fry your components and some might get more power than the others its hard to get them balanced, if you can sell them both and stick with 1 powerful PSU that would be much better and safer.
January 30, 2011 12:33:12 AM

intelx said:
yea you can run 2 in one system but i would really try to stay away from this setup as much as possible, you might fry your components and some might get more power than the others its hard to get them balanced, if you can sell them both and stick with 1 powerful PSU that would be much better and safer.



I've never seen anyone "fry" their system by doing this, or how some components could "get more power than the others", and i've seen this setup several times.
March 21, 2012 7:36:46 AM

I know this is an old post. Just to get the word out to anyone googling. This will only work if you are powering a electric isolated component. Fans, Pumps and lights are examples of electric isolation. The problem is in the way the power supplies maintain a constant voltage. The voltage control circuits looks at the output voltages and if one of the output voltages drops it increases current to raise the voltage on that circuit. This is where the trouble comes in with a second power supply. If you connect the output of one power supply to the output of a second power supply the voltage regulators on both fight one another. The way that happens is due to how well it is possible to manufacture a power supply. An example of this is no 5 VDC is 5 volts exactly. If one ups output is 5.05 and the other is 5.1 The 5.1 tries to pull the 5.05 up to 5.1 the 5.05 tries to pull the other down to 5.05. Beginning to get the picture. Soon the 5.1 is running full output trying to put the other up to 5.1 and the other is shut completely down trying to pull the 5.1 down to 5.05.

What this means is the positive outputs can not get together. The sensing circuits will not allow it. If anything plugs into the mother board other than the ground side of the supply in 99.9 % of time the sensing circuits will not work and will draw so much current it will destroy the motherboard and the power supply.
July 31, 2012 8:19:24 PM

OldMarine said:
I know this is an old post. Just to get the word out to anyone googling. This will only work if you are powering a electric isolated component. Fans, Pumps and lights are examples of electric isolation. {snip}


Thanks for updating and actually going into some depth. I've gone through at least four other threads like this with groups of responders going both ways on the answer but those who were against didn't get into so much detail.

I'm working on a system used to do some heavy rendering and unfortunately the apps I use rely only on software rendering using the CPU. (GPU is used for manipulation of objects, not rendering.) In the past I've gotten warning beeps from said CPU when it was overheating, (even on hot nights -- i.e., 3 a.m. waking me up from sleep -- when I wasn't rendering!) so I'm looking to build a new case with better airflow control than any I've seen on the market. I'm sure I can build something better than what I've had, which is a 120v desk fan next to an open case.

What I'm pondering relies on at least four case fans, plus the PSUs for air intake. Everything will flow in the same direction and if I got the floor friction down the new box would probably roll across the room, but I digress. ;)  One PSU runs MB, drives and PCIe, the other runs only itself and case fans. I have several surplus (but small) PSU's, so it's not a matter of wasting money on them, at this point.

I was wondering what you thought about the aforementioned Lian Li power adapter on Frozen CPU. I didn't really want to install the modular 24-pin cable at all on the supplementary PSU, but that adapter would need it. Might there be a simpler-but-safe way to activate both PSU's from standby?

I'm also seeing differing opinions on needing to momentarily or permanently ground the PS_ON pin, if it's not connected to the MB. Does the modern PSU care, provided no sensitive devices (besides itself) are attached?
a b ) Power supply
July 31, 2012 9:26:47 PM

grounding the ps_on line turns the PSU on. Thats how the motherbd turns on the power supply. What the adapter above does is connect the secondary PSU ps_on (and ground) to the motherbds' ps_on header. If you have any wiring ability then you see that you can do this yourself without the expense of the adapter.


edit just for clarification.
Pressing the power button on the front of the pc supplies a momentary ground to the motherbds power circuitry. Said circuitry then provides a constant ground to the ps_on line to turn on the psu. Once the psu volatages stabilize (are within spec) the psu supplies a pwr_on (5v) signal to the motherbd which signals the motherbd to 'boot up'
a c 243 ) Power supply
July 31, 2012 9:34:30 PM

VoltisArt said:
Thanks for updating and actually going into some depth. I've gone through at least four other threads like this with groups of responders going both ways on the answer but those who were against didn't get into so much detail.

I'm working on a system used to do some heavy rendering and unfortunately the apps I use rely only on software rendering using the CPU. (GPU is used for manipulation of objects, not rendering.) In the past I've gotten warning beeps from said CPU when it was overheating, (even on hot nights -- i.e., 3 a.m. waking me up from sleep -- when I wasn't rendering!) so I'm looking to build a new case with better airflow control than any I've seen on the market. I'm sure I can build something better than what I've had, which is a 120v desk fan next to an open case.

What I'm pondering relies on at least four case fans, plus the PSUs for air intake. Everything will flow in the same direction and if I got the floor friction down the new box would probably roll across the room, but I digress. ;)  One PSU runs MB, drives and PCIe, the other runs only itself and case fans. I have several surplus (but small) PSU's, so it's not a matter of wasting money on them, at this point.

I was wondering what you thought about the aforementioned Lian Li power adapter on Frozen CPU. I didn't really want to install the modular 24-pin cable at all on the supplementary PSU, but that adapter would need it. Might there be a simpler-but-safe way to activate both PSU's from standby?

I'm also seeing differing opinions on needing to momentarily or permanently ground the PS_ON pin, if it's not connected to the MB. Does the modern PSU care, provided no sensitive devices (besides itself) are attached?

You want to use a secondary psu to run a few case fans ? :heink: 
July 31, 2012 9:43:22 PM

You seem to have skipped over the questions... I know what the physical connections are and where to plug them in. I'm asking about the detailed electrical happenings within them and how to keep this mod simple and safe.

Above reply to popatim was before their edit...have to go out, will review further when I get home. I do appreciate more info -- thank you.
July 31, 2012 9:46:20 PM

delluser1 said:
You want to use a secondary psu to run a few case fans ? :heink: 


The above reply was to the previous response, not you. Yep, I do. If it gets me good airflow without bothering the primary system, I'll do it.

Note I said "at least four fans"... There may be more fans or other toys added in the future.
a c 243 ) Power supply
July 31, 2012 9:55:53 PM

VoltisArt said:
The above reply was to the previous response, not you.
I got that
VoltisArt said:
Yep, I do. If it gets me good airflow without bothering the primary system, I'll do it.

1) If your case has no option for mounting a secondary psu there will be no help from it as far as airflow, and due to the low load level you plan to place on it would most likely hurt temps rather than help them
2) If your existing psu can't handle the extra load of a few case fans it's to small and needs to be replaced anyway
a b ) Power supply
July 31, 2012 10:09:34 PM

OldMarine said:
Soon the 5.1 is running full output trying to put the other up to 5.1 and the other is shut completely down trying to pull the 5.1 down to 5.05.

PSUs have no such circuitry to "pull" outputs down in a regulated manner. Diodes or synchronous rectifier outputs will leave excess voltage where it is and dial down the duty cycle control to reduce the amount of current provided until voltage comes back down. What pull-down circuitry PSUs do have is over-voltage crowbar which shorts outputs to ground if any of them strays too far above spec, in which case the tripped PSU will attempt to pull its crowbar rail(s) to 0V.

OldMarine said:
What this means is the positive outputs can not get together.

It can work but the two PSUs' outputs have to be almost perfectly matched, close enough so that wiring resistance between the PSU and loads is high enough to provide adequate current balancing. In a real redundant/load-sharing PSU, reference and comparator outputs would be shared between units to guarantee nearly perfect balance.
a b ) Power supply
July 31, 2012 10:13:05 PM

delluser1 said:
2) If your existing psu can't handle the extra load of a few case fans it's to small and needs to be replaced anyway

^ I agree.

Fans are only 3-10W a piece depending on model and feed voltage/current, should easily fit a bunch of them in any reasonably sized PSU's headroom budget.
a b ) Power supply
July 31, 2012 10:15:48 PM

How about delta fans?
a b ) Power supply
July 31, 2012 11:43:29 PM

jay_nar2012 said:
How about delta fans?

Depends on models.

Some of their 120mm models run at 1000-1400RPM on 12V and use only 3-5W while their highest speed industrial-strength models go over 7000RPM and use 35-45W but those are 38mm thick and will not fit in some cases' fan mounts due to being too thick.
August 1, 2012 1:34:15 AM

Ooookay. Now we're getting somewhere interesting. So probably more downside than benefit...duly noted.

In general, I was looking at the problem from airflow, wiring complexity (daisy-chaining many items on one rail) and not having my old-but-decent PSU laying around doing nothing. If the wattage is really that low per fan, however, tossing 6-8 fans on one rail shouldn't be a problem. One less power supply will give me more open space and room for two more fans on that wall. (Mentioned in my first post that I'm building the case, not just assembling the comp. Every part is currently flexible.) The wattage of the primary PSU was not really a factor for this project -- New 750w that was an upgrade with my latest PCIe vid card.

Just for learning purposes...gathering from popatim's edit, while the modern case switch makes a temporary connection for the PS_ON to the MB, the PSU gets a constant connection from the MB, so a PSU without a motherboard would need a hard switch to maintain power-on status. Yes?

7000 rpm...now, that would get the box rolling across the floor. :D  Almost sounds like you could fly something with that. Pity the bulky depth.
a c 243 ) Power supply
August 1, 2012 11:01:52 AM

VoltisArt said:
Ooookay. Now we're getting somewhere interesting. So probably more downside than benefit...duly noted.

In general, I was looking at the problem from airflow, wiring complexity (daisy-chaining many items on one rail) and not having my old-but-decent PSU laying around doing nothing. If the wattage is really that low per fan, however, tossing 6-8 fans on one rail shouldn't be a problem. One less power supply will give me more open space and room for two more fans on that wall. (Mentioned in my first post that I'm building the case, not just assembling the comp. Every part is currently flexible.) The wattage of the primary PSU was not really a factor for this project -- New 750w that was an upgrade with my latest PCIe vid card.

Just for learning purposes...gathering from popatim's edit, while the modern case switch makes a temporary connection for the PS_ON to the MB, the PSU gets a constant connection from the MB, so a PSU without a motherboard would need a hard switch to maintain power-on status. Yes?

7000 rpm...now, that would get the box rolling across the floor. :D  Almost sounds like you could fly something with that. Pity the bulky depth.

Read the line, didn't take it to mean you were actually "building" the case, sorry
With a 750 watt psu you should have nothing to worry about, even if you wanted to use a few Delta's
August 1, 2012 4:01:42 PM

Cool. Thanks to everybody who's contributed to this zombie thread. I'll see about dropping a link to pics once this thing's done.

If it goes well, I may eventually offer them up for sale, customized. It won't be cheap or lightweight, but it will keep your CPU closer to room temp than most mass-marketed cases. Forgot to mention the filter...it'll keep it clean, too.
!