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Daisy chaining two power supplies

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August 17, 2010 4:18:15 PM

Hi there,

Recently I managed to salvage an old system from work which I've been adding to and improving to use as an HTPC. I've had quite a few issues with it though,

1) I bought 2 gigs ( 2 x 1gig) of DDR Ram that only register as 1 gig (I think this has something to do with the BIOS)
2) I bought a Geforce 6800GT AGP that I've plugged in and installed the drivers for...but here's the issue.

The card crashes the system! I think its quite a power hungry card, and its causing the system to die. When I log onto Windows the screen goes almost like a mosaic after the Welcome message, and then often reboots. It works in VGA mode and safe mode, but any attempt to increase resolution crashes everything.

Now I think that's because the card isn't getting enough power. I'm running an ASRock k7vm2 R3.0 motherboard with an Athlon XP 2400+ CPU, the 2 gigs of ram that think they are 1 gig, 1 80 gig HDD, 1 DVD Rom...and that's it! I've unplugged anything else that could take power including the floppy drive and a pci card that was working as an old dialup modem, however I think its not enough!

My power supply in the case is a 350W PSU with I think.....15a on the 12v rail (maybe more as I'm not at home to check right now!), and I managed to scrounge another 250W PSU from work.

My question now is:

Can I daisy chain those 2 PSUs together to give the 6800GT more juice? I know the more practical solution would just be to get a better PSU, but I'm keen to try this solution first. I've seen there are some Dual Power Supply Adpaters available on the web eg:
http://www.frozencpu.com/products/5637/cpa-167/Lian_Li_...
But my question is: can I safely just plug these two in together and go? Does the graphics card have to be plugged into either of the PSUs specifically? In addition, can the secondary power supply just sit at the bottom of the case, or do I have to somehow mount it and insulate it?

Any tips or words of wisdom from someone who knows a lot or who has done it would be greatly appreciated!
Thanks!
a c 144 ) Power supply
August 17, 2010 7:34:13 PM

A 6800GT needs only about 4 amps (48 watts). Unless your 350 watt PSU is an utter piece of crap, it should be able to run your system.

But, yes, you can daisy chain two PSU's, but none of the regulars here (including me) recommend it.
a b ) Power supply
August 17, 2010 7:43:20 PM

go with a single large psu instead of two smaller ones
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a c 248 ) Power supply
August 17, 2010 7:43:50 PM

^5 +1 what jsc said!
a c 144 ) Power supply
August 17, 2010 7:45:30 PM

Hey, Johnny. How have you been. Haven't heard from you in awhile.
a c 248 ) Power supply
August 17, 2010 7:49:35 PM

jsc - I'm doing okay. Between a little extra work that came my way, a training certification, and a new girlfriend I haven't had very much in the way of free time. I'm also getting ready to move from Scottsdale to Tucson, Arizona.
August 18, 2010 9:43:58 AM

jsc said:
A 6800GT needs only about 4 amps (48 watts). Unless your 350 watt PSU is an utter piece of crap, it should be able to run your system.

But, yes, you can daisy chain two PSU's, but none of the regulars here (including me) recommend it.


Thanks for your reply! Yeah I think my 350W PSU must be utter rubbish...as I said its a rescue PC, so I'm sure it was never intended to be doing more than pumping out spreadsheets.

Ok, so I've determined so far that it is possible to link up two PSUs...but why does nobody recommend it? Literature surrounding the idea is surpsingly sparse on the net, hence all my questions above. What would the system stability be like? And again, would I have to mount it to the case or could I just leave it sitting at the bottom of the case lying loosely?

Thanks for replies!
a b ) Power supply
August 18, 2010 10:26:58 AM

Its not a good solution one there are too many wires added to the case causing airflow problems and two extra heat added by the second power supply and the choked wired filled case is a recipe for disaster.

Now yes it is possible to power up two PSU's all you do is connect the green and black wire from the 20 pin connection and this will power up the unit with the rest of the system. Now you can use it to power your drives and run auxiliary power to the video card if it has a molex connection.
August 18, 2010 10:39:48 AM

saaiello said:
Its not a good solution one there are too many wires added to the case causing airflow problems and two extra heat added by the second power supply and the choked wired filled case is a recipe for disaster.

Now yes it is possible to power up two PSU's all you do is connect the green and black wire from the 20 pin connection and this will power up the unit with the rest of the system. Now you can use it to power your drives and run auxiliary power to the video card if it has a molex connection.


Many thanks for your info. Yeah I thought about that, but thankfully its a HUGE case and with quite a few fans...so not too worried about overheating. I've read about connecting the green and black wires, however I'm not too confident to do it with my current knowledge of electronics...not to mention my butter fingers! That's why I'm looking at the adapter cable that I posted a link to above. Will it do the same job?

But more importantly, I have a 350W PSU and I'm thinking of adding a 250W PSU. Should I run the 6800gt off the 350W or the 250W? I was thinking about running the 6800GT off the 250 and then everything else off the 350, but does it matter what amps the 250 has on the 12v rail as all its going to be doing is powering the 6800gt?

Thanks!
a b ) Power supply
August 18, 2010 10:42:57 AM

Yea that adapters fine but if you are gonna spend $14.99 plus shipping you might as well add $20 more and get a new power supply.
August 18, 2010 10:51:10 AM

saaiello said:
Yea that adapters fine but if you are gonna spend $14.99 plus shipping you might as well add $20 more and get a new power supply.


Yeah I definetly hear you on that one, but the unique position I find myself in is that I can't really get a decent power supply for cheaper than or equal to the adapter price.

I'm on quite a tight budget, having already spent money on the RAM and the card... so if there's a decent PSU around that doesn't cost the earth I'd be interested to hear about it. I live in the UK and don't really feel like paying import prices from the US.
a b ) Power supply
August 18, 2010 11:02:48 AM

Well my suggestion to you if you are gonna try it just connect the wires yourself its not that hard I wouldnt spend a dime on that connector. If you are to spend money just get a new unit.

Antec Basiq Power 350W
http://www.ebuyer.com/product/114928
August 19, 2010 12:49:10 PM

saaiello said:
Well my suggestion to you if you are gonna try it just connect the wires yourself its not that hard I wouldnt spend a dime on that connector. If you are to spend money just get a new unit.

Antec Basiq Power 350W
http://www.ebuyer.com/product/114928


Ok, I'll go for the single PSU solution. Many thanks!
!