Dual Power Supply Help/Advice

[Tmt97]

I am making this post in preperation. You see my rig desperately needed a better graphics card and I recently found a great deal on a Radeon 7950. I am trying to get my rig setup to handle the upgrade, mostly because my power supply probably cant handle it on its own. The graphics card in question has both a 6 pin and an 8 pin socket, and I've never dealt with a card that needed any cable attatched to it at all. My PSU can only plug into the 6 pin socket. Regardless, I only have a 400watt power supply anyway. I plan to purchase a new PSU later when I have the money, but for now my best bet is to try to setup a dual power supply with a spare 200watt PSU. I know some people might dissaprove of this, but sometimes you just gotta make do until you can afford to do this the "right" way.

 

Does anyone have advice as to how to safely make my 200watt, and 400watt PSU's work together? Also since I dont have an 8 pin connector for the card on either PSU, what other connectors do you reccomend converting to an 8pin with an adaptor cable?
 

Also, if I have to tinker with the power supplies, any tips on not killing myself? Mild to severe injury is an acceptable loss for acomplishing this mission, however I'd prefer to avoid instant electrocution. Thanks!

[QueenDemetria]

I am making this post in preperation. You see my rig desperately needed a better graphics card and I recently found a great deal on a Radeon 7950. I am trying to get my rig setup to handle the upgrade, mostly because my power supply probably cant handle it on its own. The graphics card in question has both a 6 pin and an 8 pin socket, and I've never dealt with a card that needed any cable attatched to it at all. My PSU can only plug into the 6 pin socket. Regardless, I only have a 400watt power supply anyway. I plan to purchase a new PSU later when I have the money, but for now my best bet is to try to setup a dual power supply with a spare 200watt PSU. I know some people might dissaprove of this, but sometimes you just gotta make do until you can afford to do this the "right" way.

 

Does anyone have advice as to how to safely make my 200watt, and 400watt PSU's work together? Also since I dont have an 8 pin connector for the card on either PSU, what other connectors do you reccomend converting to an 8pin with an adaptor cable?

Get a proper power supply, one with enough connectors and power.

[W-L]

-SNIP-

 

Theoretically you can hookup both together but it's not recommend especially if they aren't quality PSU's, it would be better to wait a bit to get a new PSU than to risk the hardware on two bad ones.

[Tmt97]

Yes, I understand the risk. It will probably be a while before I can afford a "proper" power supply, and I dont really have any measurable amount of patience... so yea. I suppose I can just try it on my own, but I figured with your advice I could reduce the odds of me breaking a perfectly good Radeon 7950.

 

edit: Come on guys! Think of the 7950, do you really want me to post a pic of it smoking later because I didnt get proper instruction on how to implement this horrible idea? Such an innocent card... it'd be a shame for it to die young.

[Naeaes]

Yes, I understand the risk. It will probably be a while before I can afford a "proper" power supply, and I dont really have any measurable amount of patience... so yea. I suppose I can just try it on my own, but I figured with your advice I could reduce the odds of me breaking a perfectly good Radeon 7950.

Dual PSUs is not uncommon at all but I have't ever seen anyone power one GPU with two PSUs. One for the GPU and one for all the rest is fine but I've proven time and time again at work that it won't even post if you have two separate rails of one PSU in one GPU so I'm having hard time believing you can power a single GPU with two PSUs. Then again, I haven't handled all the PSUs and GPUs in the world so hopefully someone will post a link that proves me wrong. 

 

A 200W PSU won't have an 8-pin (150W) connector. If it does, don't buy it. 

 

You can always get splitters and adapters and run the GPU off of your 400W PSU. You can give it a chance by using crappy resolutions and settings. The PSU will burn for sure sooner or later but it might not take your GPU and/or other components with it as it goes. Also happened in my 'lab': A GTX590 passing Heaven Benchmark running off a 300W PSU. 

[Tmt97]

Dual PSUs is not uncommon at all but I have't ever seen anyone power one GPU with two PSUs. One for the GPU and one for all the rest is fine but I've proven time and time again at work that it won't even post if you have two separate rails of one PSU in one GPU so I'm having hard time believing you can power a single GPU with two PSUs. Then again, I haven't handled all the PSUs and GPUs in the world so hopefully someone will post a link that proves me wrong. 

 

A 200W PSU won't have an 8-pin (150W) connector. If it does, don't buy it. 

 

You can always get splitters and adapters and run the GPU off of your 400W PSU. You can give it a chance by using crappy resolutions and settings. The PSU will burn for sure sooner or later but it might not take your GPU and/or other components with it as it goes. Also happened in my 'lab': A GTX590 passing Heaven Benchmark running off a 300W PSU. 

Ok, so what if I took the 400watt PSU and split the 24 pin cable in two then adapted the two new ends to 6 pin and 8 pin? Would that work, or do you think thats too much power coming out of the 24 pin cable? If that works then I can power the rest of my rig with the 200 watt PSU. Also, out of curiosity, what exactly causes the PSU to "burn" under these conditions? If you have one capable PSU powering the GPU? Just general crappy quality of the PSU, or some other reason?

[Naeaes]

Ok, so what if I took the 400watt PSU and split the 24 pin cable in two then adapted the two new ends to 6 pin and 8 pin? Would that work, or do you think thats too much power coming out of the 24 pin cable? If that works then I can power the rest of my rig with the 200 watt PSU. Also, out of curiosity, what exactly causes the PSU to "burn" under these conditions? If you have one capable PSU powering the GPU? Just general crappy quality of the PSU, or some other reason?

If it's stupid but works, it's not stupid.

 

The 24-pin already delivers power to the GPU by proxy. The PCI-E slot on the motherboard delivers the first 75W. It's relevant, I swear!

That's why some cards like your old one don't need the extra connectors. They just use less than 75W. Tapping into that connector won't give you anything extra. Usually in such weak power supply, all the 12V cables (the yellow ones) stem from a single source so it doesn't really matter where you get the power from. If you're using adapters, it's best to have many wires. Two wires have half the resistance of a single wire and so on. So this is better than this. But do note that not all of that 400W is at 12V (which is what the GPU uses). Some is allocated to 5V, some to 3,3V and so on. There should be a label where the rated values are listed.

 

It's simple math. Volts times Amperes to get Watts. What's on the PSU are maximum Amperes, what it can deliver constantly and safely. And what the GPU actually draws depends on a lot of variables but it's designed to draw less than 300W (Since it has the 8-pin (150W) and the 6-pin (75W) connectors plus the 75W via the slot) but more than 225W (since 2x 6-pin wasn't enough) So if the power supply has 25A @12V or more listed, it's enough. (300W/12V=25A) If there's less than 18,75A (225W/12V=18,75A) then it's definitely not enough. And if it's somewhere in between, you can try your luck.

 

The more Watts are pushed through the system, the hotter it gets. It'll heat up where ever there is most resistance. Usually it's one pair of the wires that heats up so much that the sleevings melts, there's a contact between two bare wires and the short blows fuses. But if the wires are sturdy enough, some other point inside the powersupply will go first. Some power supplies have over-current protection which recovers after it's given time to cool down. Some have safety diodes. Kind of like soldered-on-fuses, intended to be the weakest point.

But some have neither and the next critical components to go are capacitors. They can get extremely hot. Like set-stuff-on-fire-hot. And not only that, they're also somewhat pressurized and there's liquid inside so they really can have some kick to them as they blow. It's can be real fire-and-brimstone stuff. If you're unlucky the PSU can push a last big surge of over voltage toward the system as the components malfunction due to heat, fire and shortcircuits. That's what destroys components. Say, your RAM runs at 1,5V. It can even handle 1,65V and a bit above. But even a short surge of something crazy like 200V through the RAM will destroy every last transistor in it. Same goes for the GPU, CPU, pretty much all chips on all PCBs. Fans are often relatively safe.

[Tmt97]

If it's stupid but works, it's not stupid.

 

The 24-pin already delivers power to the GPU by proxy. The PCI-E slot on the motherboard delivers the first 75W. It's relevant, I swear!

That's why some cards like your old one don't need the extra connectors. They just use less than 75W. Tapping into that connector won't give you anything extra. Usually in such weak power supply, all the 12V cables (the yellow ones) stem from a single source so it doesn't really matter where you get the power from. If you're using adapters, it's best to have many wires. Two wires have half the resistance of a single wire and so on. So this is better than this. But do note that not all of that 400W is at 12V (which is what the GPU uses). Some is allocated to 5V, some to 3,3V and so on. There should be a label where the rated values are listed.

 

It's simple math. Volts times Amperes to get Watts. What's on the PSU are maximum Amperes, what it can deliver constantly and safely. And what the GPU actually draws depends on a lot of variables but it's designed to draw less than 300W (Since it has the 8-pin (150W) and the 6-pin (75W) connectors plus the 75W via the slot) but more than 225W (since 2x 6-pin wasn't enough) So if the power supply has 25A @12V or more listed, it's enough. (300W/12V=25A) If there's less than 18,75A (225W/12V=18,75A) then it's definitely not enough. And if it's somewhere in between, you can try your luck.

 

The more Watts are pushed through the system, the hotter it gets. It'll heat up where ever there is most resistance. Usually it's one pair of the wires that heats up so much that the sleevings melts, there's a contact between two bare wires and the short blows fuses. But if the wires are sturdy enough, some other point inside the powersupply will go first. Some power supplies have over-current protection which recovers after it's given time to cool down. Some have safety diodes. Kind of like soldered-on-fuses, intended to be the weakest point.

But some have neither and the next critical components to go are capacitors. They can get extremely hot. Like set-stuff-on-fire-hot. And not only that, they're also somewhat pressurized and there's liquid inside so they really can have some kick to them as they blow. It's can be real fire-and-brimstone stuff. If you're unlucky the PSU can push a last big surge of over voltage toward the system as the components malfunction due to heat, fire and shortcircuits. That's what destroys components. Say, your RAM runs at 1,5V. It can even handle 1,65V and a bit above. But even a short surge of something crazy like 200V through the RAM will destroy every last transistor in it. Same goes for the GPU, CPU, pretty much all chips on all PCBs. Fans are often relatively safe.

So lemme get this straight... If I go ahead and do this dual power supply method of powering my gpu, it will be a ticking time-bomb until those big capacitors inside my PSU will explode shooting boiling hot liquid and shrapnel into my computer, frying every component other than my fans at once, and potentially burning down my house?(Next time on scrapyard wars?)

That's a much better sell for buying a new PSU than what the other guy said.( "it would be better to wait a bit to get a new PSU" )

So is there a way around that little problem? Maybe some way to prevent it from pushing too many watts into the system as you said?