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Dual Power Supply Setup

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April 23, 2008 6:27:29 AM

Hi,

I have a strong suspicion that at startup my PSU is being pushed towards its upper limit - so I am getting funny startup symptoms.

Various PSU wattage calculators suggest my system load is around 600 to 750 watts. My present Zippy PSU has a rating of 700W.

So to overcome this situation, it seems I have two options

1. buy a new PSU, such as the Enermax Galaxy 1000W and power the whole system with it. But I am not a gamer and do not have a SLI or Crossfire setup that needs all the available power and connectors that cater for multiple CPUs, multiple cores and multiple video cards - which I would never need. Problem is that nowadays, most 1000W PSUs come with all this extra capability built in.

Plus I might have some difficulty in fitting the 220mm long PSU into the 220mm long PSU housing inside the case.

2. buy a second PSU say Enermax Infiniti 720W, and run a dual PSU system using the dual PSU adapter that came with the CoolerMaster Stacker T01 case (the adapter allows you to connect two PSUs such that when you turn on the main (700W Zippy) PSU, it will start up the second (720W Infiniti) PSU. I want to connect this second (700W Infiniti) PSU to the system's 10 hard drives (in RAID 5 and RAID1 plus some single disks) and 7 case fans only - it would not be connected to the motherboard. So other than the SATA and Fan (via Molex adapters) connectors, the ATX 24pin connector and the PCI-E connectors would not be connected at all. I also like the Infiniti's CoolGuard feature which would allow the system fans to remain on after power down to cool the system down.

Question I have is will the second PSU have enough load on it to start, and then will it be able to operate stably?

The reason I am unsure is because of the 12v, 5v and 3.3v rails in the PSU, only the 12v and 5v rails would be loaded by HDDs and fans, and the 3.3v would have no load at all. With all the protection built into PSUs nowadays, the PSU electronics may see no load on 3.3v rail and prevent it from starting.

Because this dual PSU is quite common (its mentioned in many forums) it seems to be a viable setup otherwise forums would telling people to avoid them. But no one talks about low loads effects on the second PSU. Maybe it is a non issue, the PSU starts and works OK. Would that be the case?

If anyone can shed some light on this issue it would be a great help and avoid my buying a Infinti PSU, having problems and having to switch to an alternative PSU solution.

Kind regards.

RomK

April 23, 2008 6:51:17 AM

Rom

I run a coolermaster stacker with 2 psu's 1x700w + 1x350w works fine now for 2 years. I have no load on the 3,3v of 350 only the fans, hhd and rom's
a b ) Power supply
April 23, 2008 7:25:44 AM

@OP

I'm not doubting what you're saying, but I am intrigued as to how 700W isn't enough power for a machine which, as you put it,

Quote:
not a gamer and do not have a SLI or Crossfire setup that needs all the available power and connectors that cater for multiple CPUs, multiple cores and multiple video cards - which I would never need.


What sort of setup do you run (just to please my curiosity!)?
Related resources
April 23, 2008 8:41:30 AM

I too am curious of your system specs. I mean i run a gaming rug on a 750w PSU with no issues, so i would assume yours should be plenty happy with a 700w PSU. Perhaps you have a dis-functional PSU.
April 23, 2008 9:06:41 AM

^ i am also curious... without some hungry GPU's to suck the power i dont know how you could possibly draw that much
April 23, 2008 11:34:11 AM

I'm guessing a lot of the OP's power draw is from the 10 hard disks at boot up. Most hard disks can use up to 30w at boot up, dropping to about 10w at idle, so he needs up to 300w just to power up the 10 hard disks. I think fans only need about 3w each and ROMs are about 5w each so they are relatively small.
April 23, 2008 12:12:37 PM

Why so much power? Capaill hit it on the head.

Let me list whats in the system.
1. Tyan serverboard with dual 2.8GHz Xeons and 2GB RAM
2. Matrox Parhelia 256 AGP and Matrox Parhelia 256 PCI-X (running in joined mode with the desptop stretched over 3x24in Dells), Audigy PCI soundblaster, 3Ware 12 port SATA/RAID PCIX controller.
3. 3 WD 74GB Raptors in RAID5 (with one as a hot spare), 2 250GB Seagate Barracudas in RAID1, one 74GB Raptor for Win Pagefile, and other Temp Folders, WD 160GB Caviar as interim storage for downloads, and two Seagate 250GB for Acronis image backups - all HDDs have a staggered spinup to avoid maxing out the 700W PSU.
4. several external USB devices.

All these were fed into the eXtreme Power Supply Calculator at www.extreme.outervision.com and depending on assumptions on the video setup the suggested PSU wattage ranged from 650 to 775W. Then factoring in efficiency gives a max load of around 950W max at startup and probably less than half that when its run up. Thats why I had to go to staggered spinups on the 3Ware card to preserve the Zippy 700W PSU until I decided which way to go with the PSUs.

Hence my original question
- one new 1000W PSU feeding everything, or
- setting up a dual PSU with the existing Zippy 700W feeding the MB, and the new PSU feeding HDDs and fans.

But I could not resolve what would happen with the second PSU because of the safety features of present day PSUs (would it fire up wil no load on the 3.3V rail and would it operate stably not being connected to the MB).

Many thanks guys, I am encouraged by irocs reply and a much wiser guy because of your inputs.

Cheers, Rom.
April 23, 2008 12:37:55 PM

You can hotwire a PSU by shorting the green and a black wire on the MB connector. If you could create a loop so that your second PSU connects to these on the other PSU which is plugged into the mainboard, as you start up it will start up the second PSU.

That is one hell of a system, you've obviously got more money than i have, but have you considered some newer drives? the sammy 1Tb's have plummeted in price and can outrun the raptors in throughput. This would mean u have less HDD's and can prolonge this issue until you need MASSIVE storage
April 23, 2008 11:46:01 PM

gow87 said:
You can hotwire a PSU by shorting the green and a black wire on the MB connector. If you could create a loop so that your second PSU connects to these on the other PSU which is plugged into the mainboard, as you start up it will start up the second PSU.

That is one hell of a system, you've obviously got more money than i have, but have you considered some newer drives? the sammy 1Tb's have plummeted in price and can outrun the raptors in throughput. This would mean u have less HDD's and can prolonge this issue until you need MASSIVE storage


You dont need to hotwire it when you can get this.
http://www.ultraproducts.com/product_details.php?cPath=12&pPath=584&productID=584

Personally i would just buy one bigger PSU but the daisy chaining 2 together will also work, it just increases cabling mess and heat.
April 24, 2008 4:25:30 AM

Hi guys,

Thanks for all your input.

Let me close the loop on a few of the points raised.

iroc
- you have the same Stacker case and as your dual PSUs are of simpler build (like my Zippy) they would be fine. But present day PSUs with all the split rails, over/under safety features tends to complicate things.

Just some of the things that I have found since I started this thread:
- If you are running two different PSUs in a dual PSU combo then both PSU with have different safety features and OCP shutdown levels which would not doubt cause problems
- If you were running 2 similar PSUs then this may be OK as all the rails will match up as well as the safety features
- Some PSUs have a safety feature where if the unit is asked to draw below say 50W upon startup then it wont fire on (in case of possible shorting) this seems to be a combined wattage draw across all the rails
- PSUs have been tested with max load on 12V rail and nothing on 5V and 3.3V and the PSU turns on fine, vice versa for each different rail so it shouldn't give problems.

I miss the days when things were simpler.

gow87
- hotwire a PSU? the Stacker case came with a dual-psu-adapter (exactly the same as the one pictured in chookmans url (http://www.ultraproducts.com/product_details.php?cPath=...) which allows the interconnection of two PSUs so that when you start the main PSU, it automatically starts the second PSU. Its exactly the same thing as shorting the black and green wires. There are identical adapters at www.performance-pcs.com.
- more money? as I said, I do not use my system for gaming, its mainly used to earn a living so I can feed my kids, so it had to be reliable and of good quality. The wisdom out there says you are lucky to get 3-4 years out of a PC (because of capacitor degradation, etc) so I was hoping this temporary dual PSU fix would keep me going a bit longer to give me time to catch up with the technology so I could decide what system next
- newer/Tb drives? you are right, when I bought this system 3 years ago, WD 74GB Raptors were the fastest available, and the mix of sizes I have were the vintage at the time - I know I could solve most of my problems (need for a big case, dual or very large PSUs, heating, etc) by getting a couple of Tb drives, but it would make me cry having to dump or Ebay off 5 Raptors which continue to serve me well

chookman
- bigger PSU/chaining together will also work? yes but because of present day PSUs with all their safety features it adds a layer of complexity to things - I believe a dual (present day) PSU might work but it seems that there might be complications and no one is 100% sure it would work OK

So if I distil the wisdom and advice, I think I have abandon the dual PSU setup and bite the bullet by getting one 1000W PSU and somehow shoehorning it into my case.

Many thanks guys, your input has made me wiser.

Best wishes. Rom.




April 24, 2008 9:27:31 AM

Hi Rom

If you run 2 psu's don't connect both to the MB that can cause problems, only power the drives fans and external equipment to the second psu.

Hope you sort it!!
May 2, 2008 2:17:48 PM

iroc is right Rom. Only have 1 of the PSUs going to the motherboard. Keep the other (bigger of the two) running the hard drives and Optical drives. The Zippy should have enough juice to run the Mobo, CPU, Graphics no problem. Hard drives are the biggest power draw in your system, and having nothing going to the 3.3 rails is no problem at all either. If it were a dead short, then the PS would not fire up, and it would go into fault protection mode.
!