AND gate

A simple logic circuit which I'm sure you can find the schematics floating around on the web

Especially since you have both 5V & 12V at your disposal.

True, or may be I can use a small CPLD or FPGA to do that.

I'm just wondering now if the drives on the second PSU could be damaged at power down because the PSU attached to the motherboard shuts off first and the drives are left powered for a fraction of a second. One of my drives (I think the DVD drive) makes a noise similar to an old floppy drive that's searching when I turn off the system.

So far as I know they wont. It used to be if you just killed power to a drive it could cause a head crash, but If I'm not mistaken, pretty much all drives are designed to auto park the heads if the drive looses power.

I agree with ripit, modern optical drives shouldn't have any problems with losing power suddenly, as long as it's not during firmware updates.

What about my Seagate barracudas?

I was actually refering to hard drives. I'm not certain that all drives do this, but I had thought that they auto park the heads if power is lost. It used to be that if power was lost (like during a power falure) it could damage a hard drive from a head crash. I'm pretty sure there are lots of people running computers without uninterupted power supplys and if suddenly killing power to the drive could still damage it, then all it would take is a power falure to damage your hard drives. I'm pretty sure (cant swear to it but pretty sure) that most if not all drive are designed to auto park the heads if power is cut so it doesn't cause damage.
Another aspect of it though. If your system does do anything to prepare your drives for shut down, it has already done it when the second power supply shuts down. I think you are fine. Fyi I have ran drives with power conected but no ide cable conected (when messing around with raid drives) so the drives have no control at all, they are just being powered up, and then suddenly power is cut, and I have never had a problem arise from it.

Ok. Thanks for the info.

I just ran across this. It looks like it might be a promising way to trully share power between two power supplies. Anyone have any thoughs on it? I really don't have the technical knoledge to understand it, but it looks easy enough to build.
http://www.procooling.com/index.php?...s&disp=56&pg=1

here is a product that I found on Tigerdirect.com,it is for hooking up two power supplies
http://www.tigerdirect.com/applicati...0462&CatId=462

and I am in the midst of hooking one up myself,as I'm thinking I'm running close to my single ps limit of 400 watts
currently running;

2 nvidia 6800 xt's in sli
amd athlon 64 3800+
2 sata hdd's
dvd drive
cd-rw drive
creative 5.1 x-gamer soundcard
2gbs ddr ram
and 4 multi-colored lighted fans
all in a clear lexan case(looks pretty cool in the dark)

Hmm I wonder if Antec read this topic their P190 case comes with dual power supplies A 650W and a 550W

http://www.antec.com/us/productDetails.php?ProdID=81900

Acer laptop screen not displaying but screen ok tested and working. any help please

This might not belong here, but since posts about the device are here? maybe a mod could move it if approiate? I designed a nice little buildable device a couple of years back (look at post 27 in this thread), to run dual power supplies quite safely. Truth of the matter is, I dont mod anymore (kids), but I just found a great use for the device that would only require simple adjustments to the design. It might be usefull as a power supply tester (If you just jump the power supply and take voltages, they may be off since some channels are underloaded and it is a switching power supply that requires load). A simple switch added to the design could facilitate starting the power supply, and unlike the power supply testers I have tried, it would provide proper load indefanatlly. The truth is though, it has a third use.... This is how I came to realise these uses. I need to power a water cooling setup. Its been dead for a while, and I have actually had replacement parts for a while. Its an empty case (no computer parts, just all the water cooling parts). So I would like to power the water cooling system (a Koolance system that draws power off the computer) without having to put parts in first (test the system). this would seem to work well. You could safely have a computer power supply run on its own and provide power to test whatever you want!!!!

Any thoughts on that (and or comments on moving this post to its own thread)?

Fyi, I don't understand building electronics either, this is simple to build, if you can solder, you can do it.

ok, the way i done it, is have the main psu powering all of the hard drives an cd drives ( i found the psu that is connected to the motherboard has to be connected to the drives. BECAUSE the devices then know when to 'get ready' to shut down ) ok... and my second psu is behind the case,it has one wire coming in from an empty pci slot, powering all fans, cathodes etc.... oh.. the second psu just has a paperclip connecting the greenwire to pin 15.

( and i didnt want to cut open any wires... )

i tried a second psu to power hard drives, but the problem then, is when the cpu turns the power off, the power is still going to the hardrive...and it doesnt want it!

Would My system (Below in My signiture) Benifit From This type Dual power Supply Setup? Especialy once i Purchase and Install my Other 2 EIDE and 4 SATA hardDrvies ? And Btw... Out Of All the Combined Space i only have bout 40 gigs Free LOL i got Lots Crap program/music/video wise ive been collecting thru the years.... .. was just curious cause i have a spare Arrow(single Rail) 500Watt PSU laying arround doin nothin.

Well Your Problem is That u dont have Both PSU's synced together... Actualy Splicing The PS-On and Ground with othewr Lead In toturials Like Previous Posts Have Mentioned.. Allows The MotherBoard to Turn on And Shut off Both PSU's What You have done Was Bypassed The Remote on Switch and make it there fore a fully powered all time PSU no more then a Lab Power Supply... You Must Link The Two Green Wires And Black Wires togethe with a Clip... and if you dont want to Cut The wires.. go to your local Auto Parts store... and purchase to blade Wire clips .. its a snap on conecter that accepts a male blade and climps on a wire.. purchase 4 of them.. and 2 male blade connecters... and normal spool wire.. you well need to determine length... but all in all... your problem is simple... and Quick connects Auto Wire clips Are The Way to Go if u dont Like to Cut Wires

Hey guys,

I recently (2 days ago) bought an EVGA 8800GT superclocked edition and realised that my psu can not run seeings that it reqires dual 12v rails with 26 total as a minimum, so i swore alot once i figured that out. once i finished swearing (13.76 hours of swearing) i thought to myself hmmmm 2 power supplies? so i crunched the numbers and thought to myself this could work. i just bought a 500 watt psu about 20 minites ago and i am going to connect it and the psu i already have to my 8800GT making it run off two psu's. i was wondering what our oppinions on this was? i will tell you guys tonight whether i have to get another 335 bucks for another 8800GT and about 200 for a power supply (good one) oh and maybe the motherboard will blow but we will see.

Cheers.

oh whoops. when i say 26 total i mean 26 "amps" total
^^

Success! it worked. i was playing crysis with evertything on high and 2xAA it looked really pretty. next week i will buy my new case and power supply. oh and also the forums weren't wrong about the overheating issue with the 8800GT superclocked edition. i have an extra fan right above my graphics card and it still got to 67 degrees celsius after about 3 hours of play lol.

Cheers.