# Double Power Supply



## KH0UJ (May 7, 2009)

I just recently bought a used BFG 8800 ultra Video Card, my PSU +12V has dropped to 11.78 volts  I was wondering if somebody ever tried installing 2 PSU in a single case? any ideas?


im gonna try it this saturday, im gonna rig the second PSU only for the Video Card, i never thought that this card drains a lot of AMPS 650W is a joke on this card WTF


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## DrPepper (May 7, 2009)

I don't think you need another psu for an 8800 Ultra. It should be fine.


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## alexp999 (May 7, 2009)

Are you using software or hardware to measure the voltages?

And what is a "Homebrewed 650 Watts" ??


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## n0tiert (May 7, 2009)

I´m using a 750W on the entire System..... works well ! got an 4870 x2 and that sucka is hungry


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## silkstone (May 7, 2009)

What cooling have you got and is it ruuning from you current PSU? an athalon + 8800 would use somewhere in the range of 350w at load. 650w is/should be plenty.

I can see your cooling in your sig, is that an external phase change your running with a vent blowing into your case? That would be powered by an external power source, right? I also don;t recognise your PSU, homebrew=homemade?


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## KH0UJ (May 7, 2009)

silkstone said:


> What cooling have you got and is it ruuning from you current PSU? an athalon + 8800 would use somewhere in the range of 350w at load. 650w is/should be plenty.
> 
> I can see your cooling in your sig, is that an external phase change your running with a vent blowing into your case? That would be powered by an external power source, right? I also don;t recognise your PSU, homebrew=homemade?



Ived modified my PSU to handle at least 30% more amps. on the +12V rails, it can run but the PSU +12 dropped about 0.27V on full load, I measure my voltages externally on my Fluke 87 multimeter, I was wondering if somebody here ever tried powering 2 power supplies on a single PC, 

My rig: http://www.techpowerup.com/gallery/2014.html


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## KH0UJ (May 7, 2009)

alexp999 said:


> Are you using software or hardware to measure the voltages?
> 
> And what is a "Homebrewed 650 Watts" ??



I measure it externally with a digital multimeter (Fluke 87) homebrewed means that I modified my 500W PSU to a 650W capacity
cause for now i cant afford to buy one big PSU, ived asked around the stores over here and the prices on the PSU i wanted is skyroketting ($300+)
thats why i change the FET`s and the high frequency transformers on the +12V rail on it and calibrate it to handle at least 30 AMPS of +12V
and now im facing voltage drops again

MY rig: http://www.techpowerup.com/gallery/2014.html


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## DrPepper (May 7, 2009)

Damulta has two psu's asfaik try dropping him a pm.


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## alexp999 (May 7, 2009)

You dont need two PSUs for that setup. One 650W would be enough. But this on obviously cant cope. What do you mean by homebrewed?


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## Maju (May 7, 2009)

> I was wondering if somebody here ever tried powering 2 power supplies on a single PC



I did it. Don't know that i'd do it again.
See below


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## KH0UJ (May 7, 2009)

*Stable +12V*

I want it to be stable @ 12.00V if possible(11.98V is acceptable), since I had already one PSU just sitting here beside me in my room (feels like its watching over me and said USE ME!!!)LOL


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## alexp999 (May 7, 2009)

But what PSU is it?


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## KH0UJ (May 7, 2009)

Maju said:


> I did it. Don't know that i'd do it again.
> See below



Can you share your comments and suggestions about it? cause im having voltage drop problems on my rig and i want to install a second PSU just for the video card,


MY rig: http://www.techpowerup.com/gallery/2014.html


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## KH0UJ (May 7, 2009)

alexp999 said:


> But what PSU is it?



The PSU ived modified came with the case i bought, I forgot the brand cause I cant read it, its a chinese name and its dropping voltage(+12V to 11.4) after Ived modified it ruin stable with my HD3450 card, now after i installed my 8000 Ultra (bought it used) its dropping again but not that much(11.73V to be exact)


MY rig: http://www.techpowerup.com/gallery/2014.html


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## alexp999 (May 7, 2009)

Right so what is this PSU rated for? Whats the brand?

It could well be an el cheapo PSU that just cant cope with a hungry 8800. Thats what it sounds like if it is dropping that much.

You would be much better off investing in a decent 500W PSU than trying to get another working just for the graphics.


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## Sir_Real (May 7, 2009)

I run 2 psu's on my pc. Its only a temporary thing but it works perfect. I just happened to have two 400watt psu's but neither alone is enough for my system so i have one in the case running the mobo & dvd drives & the other just hidden behind the case on the floor which powers the gpu & harddrive. 
The second external psu i've done the wire mod so its on without needing to be connected to a mobo & case power switch. ( Just join the green wire to any black ) 

Works perfect just dont look good ! Will do till i get round to buying a 600watt psu tho.


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## newtekie1 (May 7, 2009)

I've done it, twice actually.

The first time, I used an old 350w Antec power supply running just my two 7900GTs, back when 7900GTs were still new...  I used this to make sure the secondary power supply came on at the same time the primary one did, bad things can happen if you don't ensure this.  Of course you can make your own device to serve this purpose if you want.

Then, I bought one of these.  Which is purpose build to run only graphics cards from.  It works pretty damn well, though now that I only have a single GTX282, I had not need for it and took it out of my rig.


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## KH0UJ (May 7, 2009)

alexp999 said:


> You dont need two PSUs for that setup. One 650W would be enough. But this on obviously cant cope. What do you mean by homebrewed?



I modified the parts inside to provide me 30% extra amperage on the +12V rail, Ived opened it and change the FET`s and the transformers inside, i stumble on a dead 750W PSU on a server, I scavenge all the parts on that PSU and installed it on my current PSU


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## alexp999 (May 7, 2009)

No offence, but if it was a true 650W, it wouldnt have any trouble powering that 

My 650W powers an OC'd GTX 260. I measured the voltage on the PCI-E connector going into the card during a stress test and it was bang on 12.00v


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## Sir_Real (May 7, 2009)

Yeah must say i agree with alexp999. I have a 8800gt & a single 400watt psu does run my hole system but you could have dryed ya hair from it !  Hence i added a temporary second psu.


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## KH0UJ (May 7, 2009)

*Tight Budget*

If I had just the money, I already purchased the high end one, sometimes tight budget pushes me to do modifications to achieve the same capacity on a high end one, But this card just pushes my modified PS to the limit and i cant add anymore a bigger Transformer (chopper) because the PSU case is tight already, thats why im planning to add the second PSU to cope with the AMP load drained on my second Video Card



MY rig: http://www.techpowerup.com/gallery/2014.html


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## kurosagi01 (May 7, 2009)

no offence KhJOU you just got owned,and your 2nd rate 650w you messed it up yourself with your modification.I'm running an overclocked core 2 duo E6320 at 2.8ghz and a overclocked 9600GT on a 400w psu..you really screwed up your own psu


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## KH0UJ (May 7, 2009)

alexp999 said:


> No offence, but if it was a true 650W, it wouldnt have any trouble powering that
> 
> My 650W powers an OC'd GTX 260. I measured the voltage on the PCI-E connector going into the card during a stress test and it was bang on 12.00v



that`s the PSU i ever wanted,


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## newtekie1 (May 7, 2009)

Guys, it isn't that his PSU isn't able to handle the load, it is just not acceptable to him that it drops below 12.00v under load.  A lot of high end power supplies do this, it is actually pretty normal.  KH0UJ obviously doesn't like this, that is his right, and nothing wrong with it really.

If you look here, you will see even an 800w name brand BFG power supply, one that most of us would agree is a pretty damn good power suppply, showing almost identical behavior to what his is doing under load.

Again, he isn't saying his power supply can't handle the load, he just doesn't like that it drops below 12.0v while doing it.  Most of you probably never even notice the drop, but I bet your power supply does it.


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## alexp999 (May 7, 2009)

A decent PSU should not drop that much under load. Mine doesnt


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## newtekie1 (May 7, 2009)

alexp999 said:


> A decent PSU should not drop that much under load. Mine doesnt



I can almost gurantee that your PSU's 12v line flucuates under load, they all do.  I've never seen one that didn't.  11.75 is well within what decent power supplies drop to under load.  And since we don't know where it starts at in the first place, we can't say it really is dropping that much.  If it sits at 12v exactly under load, then dropping to 11.75 isn't a major drop, a 0.25 drop is pretty common, even on good power supplies.

I can show you Corsair power supplies droping below 11.60v under load if you wish.


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## Sir_Real (May 7, 2009)

You carnt trust the bios or software to give a true value on the 12v line anyway i've tried compairing the bios readings to a multimeter & there was like a 1 volt difference ! Think you get this with many mobos.


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## KH0UJ (May 7, 2009)

newtekie1 said:


> Guys, it isn't that his PSU isn't able to handle the load, it is just not acceptable to him that it drops below 12.00v under load.  A lot of high end power supplies do this, it is actually pretty normal.  KH0UJ obviously doesn't like this, that is his right, and nothing wrong with it really.
> 
> If you look here, you will see even an 800w name brand BFG power supply, one that most of us would agree is a pretty damn good power suppply, showing almost identical behavior to what his is doing under load.
> 
> Again, he isn't saying his power supply can't handle the load, he just doesn't like that it drops below 12.0v while doing it.  Most of you probably never even notice the drop, but I bet your power supply does it.





Finally sometime enlightenment, so i guess my PSU is alright after all, thanks guys, you really made my day if the high end ones does that then im still on the right track


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## alexp999 (May 7, 2009)

*IDLE:*






*LOAD:*


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## KH0UJ (May 7, 2009)

Sir_Real said:


> You carnt trust the bios or software to give a true value on the 12v line anyway i've tried compairing the bios readings to a multimeter & there was like a 1 volt difference ! Think you get this with many mobos.



I measured it externally on my multimeter, but i guess this is normal after all thank GOD


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## newtekie1 (May 7, 2009)

alexp999 said:


> *IDLE:*
> http://img.techpowerup.org/090507/idle.jpg
> 
> *LOAD:*
> http://img.techpowerup.org/090507/load.jpg



Run the PSU test...


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## KH0UJ (May 7, 2009)

alexp999 said:


> *IDLE:*
> http://img.techpowerup.org/090507/idle.jpg
> 
> *LOAD:*
> http://img.techpowerup.org/090507/load.jpg





Damn that`s a very stable PSU you got there, I wonder if how much is it
im sure its an expensive PSU that i cant afford


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## newtekie1 (May 7, 2009)

His Corsair is one of the best, especially when it comes to 12v stability, but throw more of a load than just a single GTX260 at it, and would bet it will drop below 12v also.

For a 450w PSU, that you modded to run far above spec, your power supply is doing pretty damn good.  Especially with running a power hungry card like the 8800 Ultra.

You should also realize that the 8800Ultra draws more power than a GTX260, they were power hungry cards.


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## alexp999 (May 7, 2009)

newtekie1 said:


> Run the PSU test...










(its right in between 12.00 and 12.01v when I took that pic


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## newtekie1 (May 7, 2009)

alexp999 said:


> http://img.techpowerup.org/090507/PSU test.jpg
> 
> (its right in between 12.00 and 12.01v when I took that pic



Still a fluctuation, I said they all do it, I didn't say they all dropped below 12v.  Your Corair is one of the best when it comes to 12v stability, but it still fluctuates.  They all do, and again I can show you Corsair power supplies dropping below 11.60v under load.

His 8800Ultra is putting his 650w power supply under more load than your GTX260 probably is, and his homemade power supply is handling it fine.  I don't know where you are getting that it can't cope with the load, it is handling it just fine.  It is perfectly normal for a power supply to drop below 12v, just because yours doesn't, doesn't mean it isn't normal.

Saying his power supply "obviously can't cope" is completely wrong.  A power supply dropping below 12v is not a sign that it can't handle the load.


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## alexp999 (May 7, 2009)

All I was saying that it should not drop that much. Decent PSUs should not drop that much.

IMO a PSU that drops that much is a sign its not coping, or is cheap

And I seem to remember you saying:

"and would bet it will drop below 12v"

"...drops below 12.0v while doing it. Most of you probably never even notice the drop, but I bet your power supply does it"

I know drop on the 12v line is normal, but down to 11.78v when read on a multimeter seems far too much for a supposedly 650W PSU.

And I'm not saying that just cus mine doesnt drop below no-one else's should , like I keep saying, the drop just seems a bit much.


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## KH0UJ (May 7, 2009)

alexp999 said:


> You dont need two PSUs for that setup. One 650W would be enough. But this on obviously cant cope. What do you mean by homebrewed?





newtekie1 said:


> His Corsair is one of the best, especially when it comes to 12v stability, but throw more of a load than just a single GTX260 at it, and would bet it will drop below 12v also.
> 
> For a 450w PSU, that you modded to run far above spec, your power supply is doing pretty damn good.  Especially with running a power hungry card like the 8800 Ultra.
> 
> You should also realize that the 8800Ultra draws more power than a GTX260, they were power hungry cards.



Thanks a lot Newtekie1, I personally calibrate my modified PSU cause i have all the tools and equipment to do the job, im a communications technician, it really can handle a 30 amp dummy load without a drop, not even.01V, on my HD3450 not a single volt, but now it drops but i guess its just normal, on idle its fine but when i start playing DMC4 test sometimes it fluctuates, to 11.73V on very high setting on everything


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## KH0UJ (May 7, 2009)

alexp999 said:


> All I was saying that it should not drop that much. Decent PSUs should not drop that much.
> 
> IMO a PSU that drops that much is a sign its not coping, or is cheap
> 
> ...



mine`s cheap bro, i bought it for only $50 including the case that`s why i mod it to hopefully cope with the load


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## alexp999 (May 7, 2009)

30 amp?

Is that on the 12v rail?

Thats not enough for an 8800 Ultra, to give you an idea, my Corsair 650W is rated for 52A continuous on the 12v rail.

I still believe if it can do 30A no drop, but the 8800 Ultra is making it drop, the PSU cant cope like it should 

EDIT:

Why are you running such a hungry card on a cheap PSU? The PSU is THE most important part of a PC, its the backbone, the bit that powers everything and has the ability to make or break your rig.

Get it replaced, no amount of modding can bring a cheap PSU up to standard, save building your own from scratch.


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## newtekie1 (May 8, 2009)

alexp999 said:


> All I was saying that it should not drop that much. Decent PSUs should not drop that much.
> 
> IMO a PSU that drops that much is a sign its not coping, or is cheap
> 
> ...



I bet I could get your Corsair to drop below 12v...

Most do drop below 12v.

Dropping to 11.78v is not a major drop, I don't know where you are getting that it is.  I can show you multiple high wattage PSUs that do similar under load.

How about a *900w* Cooler Master Dropping to just over 11.80v? Pretty damn close to 11.78v...

We've already seen the BFG 800w dropping below 11.70v.

How about a Mushkin 800w dropping below 11.80v? Pretty damn close to 11.78v.

Then how about the Xigmatek *1200w* that goes down to 11.80v under load?  Not that far off from 11.78v...

Or how about a Sunbeam Tuniq *1200w* dropping down to ~11.78v?

You going to tell me that all these high output brand name quality power supplies can't cope with the load.


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## a_ump (May 8, 2009)

My voltages are low also, on all 3.3v, 5v, and 12v. i don't mean to steal your thread at all but it's on teh same subject so hope you don't mind. but is this bad? and Alex, mine is a corsair which is supposed to be a great brand(GamexTreme 700w specifically)


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## alexp999 (May 8, 2009)

You cant go by software readings, my 12v line was 11.9v according to everest under load, lol.


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## a_ump (May 8, 2009)

ugh, dam i hope it isn't lower than that, i've had this PSU for a year and a half, i'd h8t to have to buy another before i purchase a high end card soon. what do you think newteckie?


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## silkstone (May 8, 2009)

Quick question, you measured the power out of the PSU to determine it was 650w, right? not the power in? there will be a big difference on that PSU between the 2. to get an accurate measure you really need to test all the lines. both the 12v and then the 5v. Also the 12v will be linked so you need to measure them at the same time.

btw, my 12.1 line measuere 21.1v all the time, but only in software, i don;t have the tools to test it properly.



alexp999 said:


> 30 amp?
> 
> Thats not enough for an 8800 Ultra, to give you an idea, my Corsair 650W is rated for 52A continuous on the 12v rail.



Wow, that PSU has 1 12v line and can handle 52A?? that's 624w on the 12v, leaving only 26w on the 5/3.3v line!


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## JrRacinFan (May 8, 2009)

http://forums.techpowerup.com/showthread.php?t=63026

I run dual psu every once in a while.


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## alexp999 (May 8, 2009)

silkstone said:


> Quick question, you measured the power out of the PSU to determine it was 650w, right? not the power in? there will be a big difference on that PSU between the 2. to get an accurate measure you really need to test all the lines. both the 12v and then the 5v. Also the 12v will be linked so you need to measure them at the same time.
> 
> btw, my 12.1 line measuere 21.1v all the time, but only in software, i don;t have the tools to test it properly.
> 
> ...



Its a corsair PSU, they are underrated. Reviews have shown this PSU to quite happily output 700W+ continuous


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## KH0UJ (May 8, 2009)

*Thanks Everyone...*

Thanks everyone, I really gained a lot of inputs from you, im just worried about voltage drops cause on the communication side voltage drops means (Switching Power Supply) less output on the 50 Watt 144 MHZ transmitter, every 0.5V can greatly reduce the RF output, instead of full 50w, it can only throw 40-45 watts, and the final transmitter heats up so easily cause it amplifies also the noise generated on the PSU due to the drop, that`s why im so conscious about the drop, but i think RF communications is different from a PC, its a bit similar but different LOL, every connector on a DC line on communications is a power loss, that`s why even my two 6 pin connectors are soldered directly on the PCB of the 8800 ultra, my 24 pin connector has been wiped with conducting compound on every pin just to ensure that there`s minimal power loss on the connectors, maybe that`s why the results on my multi meter and the software are exactly the same, no difference, but the multimeter is more agile and responsive, but when i ran it on a steady full load, its exactly the same, but i really appreciate and thankful to your inputs guys,
it added some enlightenment on my side...


PS:The largest PSU ived assembled is a 120 AMP. 13.8 volts with no drop at all on max load, but man, i cannot carry it by myself, the E-core tranformer is so big and heavy, my client used it as a PSU for a 200 watt linear amp + the base station, used to throw signal from the other island, ived regulate the voltage the conventional way, from 19 volts DC to 13.8 volts, that`s why i get really sensitive to voltage drops, cause i can make a PSU with no drop, but big and bulky, i guess PC`s are not that sensitive to voltage drops, if the top-of-the-line PC power supplies drops, therefore i dont have to worry after all.


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## Dia01 (May 8, 2009)

PS:The largest PSU ived assembled is a 120 AMP. 13.8 volts with no drop at all on max load, but man, i cannot carry it by myself, the E-core tranformer is so big and heavy, my client used it as a PSU for a 200 watt linear amp + the base station, used to throw signal from the other island, ived regulate the voltage the conventional way, from 19 volts DC to 13.8 volts, that`s why i get really sensitive to voltage drops, cause i can make a PSU with no drop, but big and bulky, i guess PC`s are not that sensitive to voltage drops, if the top-of-the-line PC power supplies drops, therefore i dont have to worry after all.[/QUOTE]

Higher voltages is not a desirable outcome either.  13.8v is quite high.  There is a limit also on multi-meter measurements, they can be slightily inaccurate.  If you don't get them calibrated regulary then considering mV readings, I would take with a grain salt.  I'm sure you and most wouldn't pay to calibrate their meters, me included.


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## KH0UJ (May 8, 2009)

Higher voltages is not a desirable outcome either.  13.8v is quite high.  There is a limit also on multi-meter measurements, they can be slightily inaccurate.  If you don't get them calibrated regulary then considering mV readings, I would take with a grain salt.  I'm sure you and most wouldn't pay to calibrate their meters, me included.[/QUOTE]


im talking about communication PSU, its 13.8V, but on PC power supply its only +12V


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## KH0UJ (May 9, 2009)

*Finally installed...*














now my +12V is overvolt a bit 12.02 volts on my multimeter, on full load with orthos
 its 12.00 volts, with Nvidia stress test its 12.01 volts, Devil may cry 4 performance test 12.00, but still fluctuates though, i think im just gonna leave it like this, besides its just a cheap non standard PSU after all


My rig: http://www.techpowerup.com/gallery/2014.html


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## KH0UJ (May 9, 2009)

*2nd +12V PSU*

I took out all the wires leaving only the +12V (yellow8 pcs.), Ground (Black 8 pcs.) and the PS on (Green 1 pc.) harnessed it and cut my CD Drive bracket to fit the second PSU, i cannot install another DVD Drive on this




My rig: http://www.techpowerup.com/gallery/2014.html


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## JrRacinFan (May 9, 2009)

Interesting mod. I am wondering tho ....

How the heck did you get a power cable ran for external to plug into the wall? Pics if you don't mind cause i am HIGHLY interested.


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## fart_plume (May 9, 2009)

You guys have realize some of your voltage fluctuation is coming from your ac power in(power company) they will vary the voltage on the power lines to compensate for the load on the grid so unless you have a line conditioner, or some form of power conditioning built into your psu your going to get voltage fluctuations. Good battery backup systems will have some form of line conditioning as part of the power surge protection. With lower end psu's you should notice a difference.


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## newtekie1 (May 9, 2009)

JrRacinFan said:


> Interesting mod. I am wondering tho ....
> 
> How the heck did you get a power cable ran for external to plug into the wall? Pics if you don't mind cause i am HIGHLY interested.



In the last picture he posted, it looks like the external plug wire is running cross the back, right above the motherboard tray.  I don't know the case, but it shouldn't be hard to either use one of the existing holes, or make a hole yourself in the back that the plug can fit through.


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## JrRacinFan (May 9, 2009)

newtekie1 said:


> In the last picture he posted, it looks like the external plug wire is running cross the back, right above the motherboard tray.  I don't know the case, but it shouldn't be hard to either use one of the existing holes, or make a hole yourself in the back that the plug can fit through.



Good eyes.

Thanks, still kinda want more in-depth pic of the back tho.


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## KH0UJ (May 9, 2009)

JrRacinFan said:


> Interesting mod. I am wondering tho ....
> 
> How the heck did you get a power cable ran for external to plug into the wall? Pics if you don't mind cause i am HIGHLY interested.




I just ran the AC wires through the sides and drill the other PSU to solder it directly to the other PSU`s socket connector, and put a cylindrical ferric cores on it from the beginning of the connections and the ending of the 2nd PSU connector to eliminate the noise generated by the AC lines,



My rig: http://www.techpowerup.com/gallery/2014.html


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## KH0UJ (May 9, 2009)

fart_plume said:


> You guys have realize some of your voltage fluctuation is coming from your ac power in(power company) they will vary the voltage on the power lines to compensate for the load on the grid so unless you have a line conditioner, or some form of power conditioning built into your psu your going to get voltage fluctuations. Good battery backup systems will have some form of line conditioning as part of the power surge protection. With lower end psu's you should notice a difference.





The AC lines on this one is stable cause i used the A.W.G. #12 power cord with no battery back-up, i measured it 113VAC with load and underload, I even soldered the high amperage
loads and put conductive compound on the other connectors to really ensure to have a minimal power loss on the D.C. side but no luck its still drops

Stress test with orthos together with nvidia stress test is 2.4 amps@113VAC (CPU rig only) with double power supply

Idle is 1.64 amps@113VAC (ived used an AC clamp meter to measure the amperage)


My rig: http://www.techpowerup.com/gallery/2014.html


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## KH0UJ (May 9, 2009)

I think its not that bad to use double power supply after all, cause my idle amps on AC is almost the same with the single PSU 0.01amp difference, (1.63amps on a single, 1.64amps on a double PSU) i think the 80% efficiency they refer is @ full load amps on the PSU, any ideas?





My rig: http://www.techpowerup.com/gallery/2014.html


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## KH0UJ (May 9, 2009)

one thing ived noticed on my +12V, before i installed the second PSU is the noise level on my oscilloscope(20% increase), specially on the test on orthos together with the nvidia stress test,  but after i installed the 2nd PSU it ran smooth just like its on idle noise level



My rig: http://www.techpowerup.com/gallery/2014.html


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## Chryonn (May 10, 2009)

brilliant work on the ghetto PSU set up. i remember doing something similar back in the day when i knew that having too many HDDs would tax my PSU, and graphics card, not to mention the other bits and pieces.  basically i made a little platform next to the original PSU and sat the new one on it; my case had a PSU support rail that ran the entire length of the case.  i spliced the green wires of both PSUs together and any two black wires, this would ensure that both PSUs would power up at the same time. i also adapted the AC cable to have two "kettle-end" sockets. the whole set up worked a charm; i had a combined output of 950W max. at a time when 1000W PSUs were being talked about.  so i had one PSU powering the mobo, graphics and opticals, and the other powering all of the HDDs


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