what happens when you use a weak PSU?

[pentium]

Okay, so I got myself the Sapphire HD 3850 and on the box it says it needs a 450W or better PSU with at least 18A in the 12V rail.
I look at my Thermaltake PSU and it's only a 430W box with just 18A on the 12V rail.
Assuming I plugged this card into my system, what exactly would happen?
Melting wires?
Smoke?
Computer self-destructs?
Blown fuse?
What bad things can come from overloading your PSU?

[acstech]

Re: what happens when you use a weak PSU?

The PSU goes out of spec on ripple on the overloaded lines, and takes out capacitors, destabilizes the computer, etc.

Either that, or the voltage goes down too much causing other bad things to happen.

Since the +12v line is ok with the required 18A, I'd say you'll be ok. Having not looked at a TT PSU I couldn't really say for certain though.

I would run it through 3dmark06 once and check voltages. If they're within spec and aren't dropping too much with load I wouldn't bother replacing it.

If you want to replace it, take a look at this:

http://www.newegg.com/Product/Produc...82E16817151034

[gdement]

Re: what happens when you use a weak PSU?

Those requirements are just a best guess by the card manufacturer, so if you have a good PSU and the system isn't heavily loaded by other stuff, then you're probably fine. I'm not sure how conservative they are when they write those requirements.

[pentium]

Re: what happens when you use a weak PSU?

Whoops, my mistake.
Actually the card needs 30A on the 12V rail and my PSU can only deliver 18A.

[stevo1210]

Re: what happens when you use a weak PSU?

If it requires 30A and you only have 18A on the 12V line... it is possible that the MOSFETs etc. will start to burn up. But seeing as this is a Thermaltake PSU, it will probably have a safety cut out before anything goes wrong. I have a Thermaltake as well and they are well built.

[Scenic]

Re: what happens when you use a weak PSU?

well... i tried to use a 250W Fortron (recapped) in my P4 sys as i didn't have stronger PSUs at hand at that time..

it's my testing system for almost everything...

after adding some HDDs and a GF6600 it randomly locked up (total freeze) or shut down (as if you unplug the power)...

replacing it with a 400W Delta Electronics solved the problems

oh.. and the voltages with the forton were extremely flaky... and the psu fan was running on top speed all the time.. but still didnt manage to keep the psu cool enough (could barely touch it )

wires were "cold" though.. no melting or something..

[pentium]

Re: what happens when you use a weak PSU?

Well then.
I guess when I go and look for two matching 500Gb Sata drives I'll also have to be looking for a new PSU as well.

[zandrax]

Re: what happens when you use a weak PSU?

I think your 3850 don't really draw 30 A on the 12 V line: it'd be a 360 W consumption for the videocard alone, you'd hear a turbojet-like fan spinning at 12000 rpm all day . WOOOOOOOSH!
These are power requirements for an high loaded system and for cheap psus with fake ratings on their labels: AMD and nVidia are well aware than, in best case, most people simply read the psu labels, check only wattage and buy the cheapest one with the wattage they need (in worst case they skip the first part and buy the cheapest at all), so they make high requirements to avoid people returning a new card burned by a sub-average grade smps with fake "500 W" labels.
If you read any review, you'd discover that most mid level gaming systems draw near 200W at load, so the 30A requirements is unreasonable according to mere consumption. I think the 3850 shouldn't draw more than 80-90 W at full load, so 7-8 A on the 12 V line.
What exact Thermaltake model do you own? IIRC, Thoughpower ones are CWT and are decent, rated quite near their limits (so a 430 W is a good 350-400 one); Purepower and TR/TR2 are made by other manifacturers and they don't deliver what they promise. Check reviews at Jonnyguru, it may be listed here.

Zandrax