CAn I use a second AT power supply to runs fans and hard drives

[santar72]

Has anyone tried to use a second AT power supply to runs their fans, cd-roms, and hard drives? I was thinking about doing this since I was going to add two more hard drives to the computer and I don't think my Antec 350 is going to be able to handle an oc xp2100+, dual channel 1 gig ram, geforce 4, 4 160 hard drives, 1 dvd, a dvd burner, and a zip drive. I have room to add another ps just below the atx power supply and wanted to know if I can use an old at power supply that has an on/off switch to power the fans and hds before I start cutting and drilling the case.

 

[Slappy00]

ok well most power supplies will not work without a motherboard attached, but you can short two pins (4 and 6 on a 20pin atx power supply) to get the ps to power your devices. You can alos setup a switch on that short. Thats what I would do at least.

 

[jhu]

you can if you use an at power supply. for an atx power supply do what slappy00 said

 

[bjc112]

I think you would be better off to sell your Antec 350 and buy a another Antec, Sparkle or Enermax 450...

That should be PLENTY of juice.

 

[MangoTBG]

I'd probably just stick with the 350 PS. I have a 350 Enermax that powers

80 gb wd 8mb cache
200 gb wd 8mb cache
80 gb wd 2mb cache
dvd+/-RW
Dvd-rom
40xcdrw
ati 9800pro
OCed P4
highly OC 2x256 OCZ el Gold PC3700 @ DCDDR500 @ 2.8vdimm
audigy2
floppy
multiple usb devices

oh, and my fans consist of 120mm delta fan, 2x80mm ThermalTake SCF2s and 2 generic 80mms

I think we are pretty even, if not, I may have more power needs (considering the 9800pro and extra optical)

 

[Slappy00]

didnt see the AT part of your question... man I can't even remember the last time i saw an AT ps

 

[santar72]

I know you have to short out the two pin on an atx power supply. I think they even sell a 12V relay at radio shack that you can splice into the two power supplies to make them both turn on at the same time when you turn on the computer. There are some other problems that can come up but I won't go into that. Anyway I want to use an AT power supply. It has a seperate on/off switch that I think should turn the ps on and off, but I not quite sure?

 

[mechBgon]

I have to wonder what will happen if the two PSUs decide to fight over whose version of 5V and 12V is the correctly-calibrated one. 😕

 

[santar72]

Originally posted by: mechBgon
I have to wonder what will happen if the two PSUs decide to fight over whose version of 5V and 12V is the correctly-calibrated one. 😕

Thats one of the reason why I'm staying away from two atx ps. I figure since the at ps isn't attach to the mb board at all and just supplying power to spin the hds and fans it should be fine, but I not quite sure.

 

[McCarthy]

Yeah, it'll be fine. No different than having an external drive where it's on a different power supply circuit. Just remember to start the AT drive first so the drives are spun up when you boot the computer.

 

[DannyBoy]

Would I be correct in thinking you just have to short any two black wires attatched to the ps to get it to switch on? 😕

 

[Soulkeeper]

you can use an at psu that way
also you can rig an atx psu to run without it being attached to a motherboard
although it is usually not the 12v rail that is maxed out first in my experience

 

[montyw]

I would be worried about ground loops within the entire power system.
"Ground loop is a condition where an unintended connection to ground is made through an interfering electrical conductor. Generally ground loop connection exists when an electrical system is connected through more than one way to the electrical ground. " Written and copyright by Tomi Engdahl 1997-2000 www.hut.fi/Misc/Electronics/docs/groundloop/index.html
Also check with www.arrl.org

Caused me many problems in past . Very subtle problems usually turned up to be large current spikes between 2 points in ground system. You could see it on an oscilloscope.

Check out manner of connection used in redundent systems where power is supplied by both power supplies at once.There will probably be a single large ground strap where all the ground wires are attached.
Hope it helps.

MontyW

 

[ClearToLand]

A couple of questions / comments based on my experience with / knowledge of AT P/Ss (and with a book open in front of me!):

• Originally posted by: DannyBoy
  Would I be correct in thinking you just have to short any two black wires attatched to the ps to get it to switch on? 😕

  All black wires are Ground and (I'd think) connected together inside the P/S. Shorting any two outside the P/S would do nothing.
  

• Originally posted by: Soulkeeper
  you can use an at psu that way
  also you can rig an atx psu to run without it being attached to a motherboard

  I was under the impression that all switching power supplies required a load on the output or they would get squirrelly / unstable. If only +5VDC and +12VDC were being used, wouldn't it be advisable to put a couple of load resistors on the -5VDC and -12VDC lines?
  
• AT P/Ss have a Power_Good signal on P8-1 that controls the RESET line on the processor. It might be a good idea to put a 5VDC relay's coil on that pin and ground, and (if ATX P/S have the same pin) cut the Power_Good signal on the original P/S and splice it through the N.O. contacts on the new relay, creating a Boolean AND (possibly the N.C. contact might have to go to Ground to force the RESET line low).
  

• Originally posted by: montyw
  I would be worried about ground loops within the entire power system.

  If you attach the AT P/S to the frame of the computer case, everything would then share the same ground. Otherwise, run a wire between the two P/S cases, and/or between a black wire on each P/S. Make sure each P/S is plugged into a grounded outlet (no cheater 3-prong to 2-prong adapters) so that HOT and NEUTRAL don't get accidentally reversed.

santar72, if you do go ahead with two power supplies, let us know how you make out...

 

[ROcHE]

I have a 300 watts PSU powering this :

Abit NF7-S
Barton 2500+ o/c to 3200+
Radeon 8500
Hard drive
DVD-ROM
CDRW
5 case fans

No problems.

 

[garaget]

I think you should try using the current psu to power your extra stuff before you even consider using the AT psu.

If you have to buy another AT psu just to power your fans+hds why not just buy a AC/DC 12v enclosed output psu (10-15 dollars). Unless you already have an AT laying around catching dust. Then just do what you need to do.