Geforce 9400 GT

By StuCazz ยท 10 replies
Jan 22, 2009
  1. I have an older system and I need to change my Dell psu to a new one, in order the run a better graphics card. The card, Geforce 9400 GT, requires a minimum of 18 amps on the +12 volt rail. My question is, what is that and how do I choose a psu which exceeds that? Is it safe to assume newer psu would meet that, what do I look for?

    Thank you in advance :)
  2. LinkedKube

    LinkedKube TechSpot Project Baby Posts: 3,485   +45

    well. watts=volts x amps. There's a max current for the 12+ rails on the psu. You can trust as long as you buy a decent psu you should be fine. I'd say 550 watts or better. Usually the volts are always listed on the box or if you're buying online they will be listed in a picture(most of the time) on the side of the psu.
  3. captaincranky

    captaincranky TechSpot Addict Posts: 13,023   +2,556

    That card doesn't actually draw more than 50 Watt on it's own. Nvidia is claiming a 300 Watt minimum PSU requirement. So, the stock PSU would likely run the card just fine. (I'm hoping that your comp has at least a 300 watter in it).
    Newegg has these 2 Antecs on sale EA-430 EA-430 or EA-380
    The EA-380 is the best deal this week. (last week it was the EA-430 @ $39.95)

    Here is Nvidias spec page on the GT9400

    A PSU's capacity is reduced with age, so even if your PSU meets the criterion for running the machine, it's probably the best approach to pop it out and treat yourself to a new one.
  4. StuCazz

    StuCazz TS Rookie Topic Starter Posts: 45

    Again, I'm unsure, what under a PSUs specs would show this,18 amps on the +12 volt rail? You say 550watts should be ok, but what if it's lower than that? Could you please let me know what to look for?

    thank you
  5. captaincranky

    captaincranky TechSpot Addict Posts: 13,023   +2,556

    Stu, either of the 2 Antec units I linked for you will develop sufficient power on the 12V rail to power your machine. As much as I am loathe to contradict Mr Smash, he does play with high performance machines all day long, and this might explain his "enthusiasm" with your actual needs. Nvidia (the peokple who actually manufacture the card), state that a 300 Watt PSU is sufficient for a 9400GT video card. I linked that page also.

    As I said before, PSUs lose capacity over time. So, it might behoove you to replace your stock PSU. Third time, either of the Antec supplies I linked wold power yor box in grand fashion! The EA-380 is on sale for 35 bucks,
  6. StuCazz

    StuCazz TS Rookie Topic Starter Posts: 45

    Indeed and thank you,

    the reason I asked how I would know, is because I couldn't just get any power supply. Unfortunately, because I have a Dell (junk) I had to pick a PSU that had the power cord in a certain place. The ones you linked were on the wrong side, but that was my fault as I didn't explain that. You were correct, I could of used my current psu, but it was old and it did not have a PCI-e connector, that's the big reason. Anyway, if your interested, I ended up ordering this

    Thank you
  7. Rage_3K_Moiz

    Rage_3K_Moiz Sith Lord Posts: 5,443   +38

    You should not have any problems IMO, although the 9400GT does not require an extra power connector due to the extremely low power draw. So you need not have bought a new PSU at all. 50W is nothing at all, and any 250W PSU will also be able to handle the card very easily.
  8. captaincranky

    captaincranky TechSpot Addict Posts: 13,023   +2,556

    I wasn't actually aware that a 9400GT had a separate power connector. I'm running a 9500GT (by EVGA) and to my knowledge it doesn't have one.
    Yes, the older Dells do have some compatibility issues with respect to non-OEM PSUs.

    I'm sure the Rosewill will power the machine handily. There is only one consideration, but it may only be of academic interest. When a PSU is under-loaded, it's efficiency suffers. Antec claims that actual draw of the system should be somewhere near 70-80% of the installed PSU capacity.

    I have taken to linking to this Antec Corporation PSU calculator page, and if you have a couple of spare minutes, you might give it a look see.
  9. Rage_3K_Moiz

    Rage_3K_Moiz Sith Lord Posts: 5,443   +38

    That is untrue cap. Efficiency drops under increasing load because of increasing heat output from the PSU components. Since a PSU's efficiency is the ratio of its DC power output to its AC power input, more heat produced means less usable DC power produced, which lowers efficiency.

    For PSUs, it all comes down to how they are labeled. Some power supplies might say "70% minimum efficiency at maximum load." Another might say, "maximum 80% efficiency." Which power supply is more efficient? Would you believe it if they're both the same? Two power supplies, from the same factory, can be labeled differently by two different marketing groups.
  10. StuCazz

    StuCazz TS Rookie Topic Starter Posts: 45

    As far as the calculator, I'm clueless, sorry.

    How could the same PSU be labeled differently from different manufacturers, that sure as heck would confused, a confused guy such as me.
  11. captaincranky

    captaincranky TechSpot Addict Posts: 13,023   +2,556

    Well, this is a trite, but unfortunately true statement; because they want you to give them your money for their merchandise. Business can be an ugly thing.

    "Cooking" the specs is a practice that has been with us for years. Manufacturers have methods to make the customer see exactly what they want them to see and it's a long, no, very long, seamy story. The FTC stepped in with legislation about reporting the power output of an audio amplifier, so that the RMS power claim must be reported. RMS is the same type of measurement (in reverse) that you would use to measure the draw of a light bulb! Basically, if you say that the amp puts out 75 watts, then the POS better damn well light that 75 watt light bulb. period.

    The PSU calculator probably needs another couple of tries on your part. Basically tell it what you have, then it'll tell you what you need. Beyond that it's just a question of knowing what components yoy have, so you 'll know what to tell it. At this point, the PSU Calculator, at least for the time being, is moot, since you have all ready purchased your unit. As I mentioned earlier the 600 watt Rosewill will certainly power your system admirably. My crystal ball is on the fritz, and I have no personal experience with that product, so who knows what the future holds.

    The only Rosewill product I personally own is an variable speed 120mm case fan, and I suppose it seems nice enough. (Active fan speed control, not just a variable resistor like some).

    @Rage; PSUs do have different efficiency ratings @ different demand levels. The issue of sagging output as operating temperatures is another matter. So, both statements (yours and mine) are true. Actually fitting a PSU to a system, I think the ideal is somewhere around 25/30% more than the maximum actual load. That is perhaps the point where deference to temperature rise meets terms of money and materials. But of course, who knows?
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