Need Psu Info Please

[iamarto]

How can I make sure that my 400 watt psu with 16 ampere on 12v+ rail will be able to run my BFG 7800 GS AGP card without performance or stability problems?

I have:
- 1 Samsung HDD 160 Gigabyte
- 1 Optical DVD drive 16 x
- Pentium 4, 3 Gigahertz HT, 1 mega-cache
- 2 x 512 Mb Kingstone Ram.
- MSI motherboard (BBG)
- Hansol 19" monitor
- Microsoft Keyboard and Samsung optical mouse

Based on this site:
http://forum.ncix.com/forums/index....nt=15&subpage=1

I have concluded that my 7800 GS will consume about 4.25 ampere from the 12v+ rail.

The only thing that confuses me is that BFG recommends 20 ampere on the 12+ volt rail. Why? And what is the REAL estimated ampere usage for my card?


My PSU specification: From Topower.com
TOP-400XP

DESCRIPTION:

* 400 Watts Pentium Ready Power Supply
* 20 pin + 4 pin ATX-12V Power Connector
* Single Sleeve fan design
* Thermal Fan Control for low noise
* Japan-Iron Case
* OVP/OCP/SCP on all 6 DC Outputs

DIMENSION (L x W x H):

Metric 145 x 150 x 86 (mm)
English 5.7" x 5.9" x 3.3"

SPECIFICATION:
Input Voltage

Selector:
95~132 Volts or 190-264 Volts AC

Output Voltage
+3.3V +5V +12V -12V -5V +5SB

Max Current Output
26A 40A 16A 1.0A 0.8A 2.5A

Max Combined Wattage
220W 192W 12W 4W 12.5W

Total Wattage 400W

 

[Big B]

You can't make it provide more power than what it already does. BFG is using nVidia's specifications, not just pulling something out of the air.

I'm not entirely sure how you came to the conclusion that the card need 4.25A either. The AGP slot provides some wattage, but the 7800GS requires more, and you'll notice a power connector on the card. That's where it takes off the 12V to supplement the extra power it requires. If it cannot draw enough supplemental power, then you're looking at stability problems. The CPU is one component that draws off the 12V.

The 20A minimum, while you might be able to get by with less, is part of the minimum requirements.

Outside of modifying it yourself---which I would not recommend doing for safety reasons, not to mention voiding your warranty---you can't make it provide anymore than what it's spec'd.

Unlike software, hardware can't be patched. Yes, components with a BIOS can have the BIOS updated, but the hardware itself can't be. The only way to update hardware is to get a new part.

So, in a round about way I'm telling you to buy a new PSU.
Go ahead and give it a shot with your current one, but don't be surprised if you run into trouble.

 

[iamarto]

Big B, thanks for giving consideration to my post.

I'm not entirely sure how you came to the conclusion that the card need 4.25A either..

I did a small calculation based on this link:
http://forum.ncix.com/forums/index....nt=15&subpage=1

7800 GS = 51 watt

watt = volts x ampere, then..

51 watt / 12 volts = 4.25 ampere

I am not sure if this calculation is accurate enough, so correct me if I am wrong.

Using this same calculation method and based on another link of the wattages I have calculated the total amount of ampere that will be used from my 12 volt rail: Re: How to know if a power supply unit would supply enouth power for 3 HDDs, a DVD-ROM and

and here are my results:

4.7a for the 7800 GS card
2.1a for DVD ROM
1.7a for HD
0.3a for CPU FAN
6a for P4 CPU

Overall amperes used = 14.8 = 15 amperes.

Which means.. only one ampere will be left :) bad news uh!?

 

[Big B]

Okay, I got the link. Yeah, the math looks right...

You don't want to be right at the edge for a few reasons.
1.)PSU's, no matter how good they are are not 100% efficient, the better ones doing 80%, possibly a little higher.
2.)In the case of multiple 12V, you'll notice that the combined output does not equal the individual outputs by themselves. The wattage rating should affect this, but not all companies do. A crappier power supply may be rated at an unattainable maximum (like 600W @ 25*C, but do 350W @ 50*, which is closer to reality, unless you keep the system in very cool conditions).
3.)I forget the exact wording and math, but in order to start up, a certain level of power is required (the amount varies on the components in said system). The system may fail to power on at all or only start certain components, usually the fans, but not boot the rest of the system.

You may be able to boot fine, but given how close you are to the limit without the big "IF"s I've mentioned, your walking on thin ice.

Plus, a good power supply is an excellent investment in the health of your components.

 

[iamarto]

Well, after a lot of research into the Egyptian market, I found only one genuine power supply that you recommended in the PSU Sticky: HEC

HEC: Ace Power 480 Watt dual rail. Hopefully that would be suffice, I hope.

EXTREME Overclocking - HEC ACE Power 480W Power Supply Review - Page: 8 - Tweaking PC Hardware To The Max

Thanks for the advice Big B.

For the sake of information, there was also an original seeming Mediatech and 1.piat power supply but I did not want to risk a product non-existing on the internet.