Gtx 460 on 400w psu

[hstpctech]

Hi,

I'm planning on acquiring a GTX 460 on my system which still using onboard HD 4200. Latest reading on $500 gaming PC (http://www.tomshardware.com/reviews/diy-gaming-pc,2970.html) which couples an Antec Earth 380w with Radeon 6850 makes me wonder if my current PSU is actually capable to drive a 460. Following is my complete spec.:

Athlon II X4 620 (non OC)
Gigabyte 785GT UD3H
4 SATA green drives
2 DVDRW
SAGA II 400W 80%
- 3.3v at 24a
- 5v at 15a
- 12v dual rails at 17a each
- max combined power at 336w
- peak power at 450w
- total power at 400w

Considering HD 6850, GTX 460, and GTS 450 are rated at 25a, 26a, and 24a respectively, and an Antec 380w being able to drive a 6850, I dared to take a wild guess that my 400w will also be sufficient enough for a 460.

Also I have been confirmed by the SAGA people and a couple of forums that the particular PSU is good enough for GTS 450.

Of course, my last concern would be that the PSU is only supplying one 6pin PEG so that second PEG would have to come from a molex converter. Should I be worry about this?

cheers,
andy

 

[rolli59]

It will probably do it since it has combined 28amps on the +12 volts (336watts) http://www.tomshardware.com/reviews/power-supply-psu-80-plus,2746-4.html

 

[hstpctech]

It will probably do it since it has combined 28amps on the +12 volts (336watts) http://www.tomshardware.com/reviews/power-supply-psu-80-plus,2746-4.html

I'm also inclined to your opinion; my only concern would be the second PEG as every articles out there suggest they should came directly from the PSU instead of molex converter. Also, do you think the left over 2 amps is enough for the rest of the system considering I also have 4 green sata drives..

 

[delluser1]

I'm also inclined to your opinion; my only concern would be the second PEG as every articles out there suggest they should came directly from the PSU instead of molex converter. Also, do you think the left over 2 amps is enough for the rest of the system considering I also have 4 green sata drives..

You're assuming that the card will use 26 amps, it won't, not even close.

 

[hstpctech]

You're assuming that the card will use 26 amps, it won't, not even close.

Well now this is new I have to admit Would you care to explain a bit more on that, since I have stumbled upon some articles stated a GTX 460 is only using 13 amps, and some said 26 amps (which is exactly twice the amount earlier stated). And it's not only particular to 460, I've seen it described as such for other cards. Exactly twice the amount.

 

[rolli59]

The 26 amp on the +12 volt rail requirement is for total amps available to the whole system!

 

[hstpctech]

The 26 amp on the +12 volt rail requirement is for total amps available to the whole system!

I think I'm getting it, you meant that the articles that stated a GTX 460 would need 26amps, it's system-wide requirement. So I guess 3 additional green SATA drives wouldn't be much of a burden, would it?

 

[rolli59]

No they would not!

 

[hstpctech]

No they would not!

Now I'm officially confused sorry but I would very much like you to elaborate a bit here... in some articles I've understand the amps requirement are meant for the whole system including the video card itself. I assume on most systems we only found one or two SATA drives, so how much additional drives would increase the total power requirement? If I recall, a single SATA drive needs 2 amps..

 

[yummerzzz]

Why don't you just get a HD 6850, less power usage, better performance.

 

[hstpctech]

Why don't you just get a HD 6850, less power usage, better performance.

Well 6850 is sold for 33% more than a GTX 460 where I currently live, so there's your reason According to MSI forum, 6850 is only one ampere less than 460.

 

[rolli59]

Here are some numbers for WD green peak loads at 1.75 amps (depending on size). http://wdc.custhelp.com/app/answers/detail/a_id/1679/related/1/session/L2F2LzEvdGltZS8xMzA5MTA0ODczL3NpZC9jUmtVcnV4aw%3D%3D Your computer use is different if you have all three HDD working at peak loads at the same time. It is more likely to estimate an average load of 6 watts per drive which would be 0.5 amps coming from the + 12 volts.

 

[hstpctech]

Here are some numbers for WD green peak loads at 1.75 amps (depending on size). http://wdc.custhelp.com/app/answers/detail/a_id/1679/related/1/session/L2F2LzEvdGltZS8xMzA5MTA0ODczL3NpZC9jUmtVcnV4aw%3D%3D Your computer use is different if you have all three HDD working at peak loads at the same time. It is more likely to estimate an average load of 6 watts per drive which would be 0.5 amps coming from the + 12 volts.

I actually employ 4 green drives, three 640GB and one 2TB. Daily usage pattern would be two drives operational and two at idle or sleep state since they are only for backup purpose.

Combining your suggestion with [delluser1]'s, then it would be safe to assume my current configuration is feasible for a 460 upgrade, yes? Do I need to worry regarding the second 6pin PEG which comes from converted molex?

 

[rolli59]

The molex adapter is a common solution so no worries and I say it should work fine. Here is an overclocked full system load I7 9xx with GTX460 running Furmark (which is a load case not seen in normal use) 331watt http://www.anandtech.com/show/4344/nvidias-geforce-gtx-560-top-to-bottom-overclock/15

 

[hstpctech]

The molex adapter is a common solution so no worries and I say it should work fine. Here is an overclocked full system load I7 9xx with GTX460 running Furmark (which is a load case not seen in normal use) 331watt http://www.anandtech.com/show/4344/nvidias-geforce-gtx-560-top-to-bottom-overclock/15

I must say you guys have been extremely helpful, and such a prompt responses too. Thank you all for the solid explanations.

 

[hstpctech]

Best answer selected by hstpctech.

 

[ko888]

Of course, my last concern would be that the PSU is only supplying one 6pin PEG so that second PEG would have to come from a molex converter. Should I be worry about this?

Yes you should be worried about this.

Without any details on which connectors are wired to which of the +12 Volt rails you can run into problems if the 4-pin Molex connector cable(s) are wired to the same +12 Volt rail as the PCI-E supplementary power cable. If that were to be the case all of your hard disk drives, CD/DVD drives, chassis cooling fans and graphics card would be drawing their +12 Volt power from the same rail which could cause the over-current protection circuit to be triggered shutting down the power supply.

 

[hstpctech]

Yes you should be worried about this.

Without any details on which connectors are wired to which of the +12 Volt rails you can run into problems if the 4-pin Molex connector cable(s) are wired to the same +12 Volt rail as the PCI-E supplementary power cable. If that were to be the case all of your hard disk drives, CD/DVD drives, chassis cooling fans and graphics card would be drawing their +12 Volt power from the same rail which could cause the over-current protection circuit to be triggered shutting down the power supply.

Thanks. This is actually a very real problem in my case.. unfortunately the PSU is not modular, and there's no additional information on which rail connected to which connector. So if I may, would you know any safe way to test for it, anything better than to risk triggering an overcurrent?

 

[ko888]

Thanks. This is actually a very real problem in my case.. unfortunately the PSU is not modular, and there's no additional information on which rail connected to which connector. So if I may, would you know any safe way to test for it, anything better than to risk triggering an overcurrent?

Since I couldn't find any reputable technical reviews on the FSP Saga II 400, where the reviewer actually does a tear-down to determine these things (i.e. load distribution), there really is no easy way of determining this without actually opening up the power supply and looking at where and how the wires are connected.

A single PCI-E connector means that particular connector has a maximum +12 Volt current draw of 6.25 Amps. If the 4-pin Molex cables were wired to the same rail that would leave 10.75 Amps for those devices.

 

[hstpctech]

Since I couldn't find any reputable technical reviews on the FSP Saga II 400, where the reviewer actually does a tear-down to determine these things (i.e. load distribution), there really is no easy way of determining this without actually opening up the power supply and looking at where and how the wires are connected.

A single PCI-E connector means that particular connector has a maximum +12 Volt current draw of 6.25 Amps. If the 4-pin Molex cables were wired to the same rail that would leave 10.75 Amps for those devices.

Will this link http://www.tomshardware.com/reviews/power-supply-psu-80-plus,2746-4.html help? I know the review didn't includes load distribution and rails related issue...so I'm pretty much busted here unless I find a howto manual to track down the rail assignment?

 

[ko888]

Will this link http://www.tomshardware.com/reviews/power-supply-psu-80-plus,2746-4.html help? I know the review didn't includes load distribution and rails related issue...so I'm pretty much busted here unless I find a howto manual to track down the rail assignment?

That review is pretty much useless.

 

[hstpctech]

That review is pretty much useless.

okay so I have to head back googling some more then... any progress will be posted here.

 

[ko888]

okay so I have to head back googling some more then... any progress will be posted here.

Since the FSP Saga II 400 adheres to the ATX12V V2.3 specification its 28 Amps will be distributed accross the two +12 Volt rails in accordance with that specification as follows :

12V1 - P4/Aux Connector (i.e. CPU Power)

12V2 - ATX 20(4) Pin Connector, Molex, SATA, Floppy and one 6-pin PCI-E connectors

This power supply is not meant for those users running a lot of high draw components. It is only meant for light to medium duty use so as to not run into a current limit issue.

This is the type of scenario where a single rail design has the advantage.

 

[hstpctech]

Since the FSP Saga II 400 adheres to the ATX12V V2.3 specification its 28 Amps will be distributed accross the two +12 Volt rails in accordance with that specification as follows :

12V1 - P4/Aux Connector (i.e. CPU Power)

12V2 - ATX 20(4) Pin Connector, Molex, SATA, Floppy and one 6-pin PCI-E connectors

This power supply is not meant for those users running a lot of high draw components. It is only meant for light to medium duty use so as to not run into a current limit issue.

This is the type of scenario where a single rail design has the advantage.

I see a bleak future here...since every molex is drawing from the 2nd rail, I have no way to access the other then?

 

[ko888]

I see a bleak future here...since every molex is drawing from the 2nd rail, I have no way to access the other then?

You're stuck with the power supply design that FSP has limited you to.

If you were willing to invalidate your warranty and you have power supply design knowledge you can open up the power supply and do some rewiring.

Thermaltake has run into this exact issue with one of their power supply models when they placed two PCI-E connectors on the same rail so that the power supply would conform to the ATX12V V2.x specification. Later they made a revision to the design so that it didn't conform to the ATX12V V2.x specification any more by rewiring the PCI-E connectors so that they obtained some of their power from both +12 Volt rails and changed the label on the power supply to show the change in the load distribution. Bad design decisions cause a lot of RMAs forcing a redesign.