Power problem, new PSU needed?

fish99

fish99

fish99

Soldato
Joined
19 May 2005
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Location
Doncaster
Hi,

We've got 2 PSUs in the house powering two PCs. They are both Enermax, one is a 475W noisetaker with dual 12V rails (15A, 16A), the other is a 465W Enermax but not one of their main lines, and has a single 12V rail of 34A.

The problem is the noisetaker is unable to power my 8800 GTS. The system switches off under load. It's definitely a power problem. I've had the problem before with this noisetaker with both an X800 XT and X1800 XT, and consequently we had to put the noistaker in the 2nd PC which uses less power and use the other cheaper Enermax in my system (which works even though it has a 10W lower rating).

Can somebody explain why dual rails of 15A and 16A can't run an 8800 GTS on a system that probably uses under 300W? The 8800 GTS accept two molex inputs into it's 6 pin adaptor and I've tried every combo on earth without luck. I just don't get it. We're just about to upgrade the 2nd system to an 8800 GTS too but obviously that's not going to work.

So the fact is we need a new PSU, but I'm worried about getting another with multiple 12V rails, and most of them seem to have multiple rails these days. Don't want to spend the earth on one though, maybe £50-60 and it's got to power 8800 GTS / Core 2 Duo 2.6 GHz / 2 GB DDR2 6400. Of course the noisetaker should power that system fine too :rolleyes:

Anyway, all recommendations welcome, and if anyone knows what's up with the nosietaker please tell me :)
Cheers,
Simon.
 
The way your Noisetaker is behaving is a bit puzzling really...you could conceivably have been hitting the 15/16A limit on one single rail with the kit that you have, but by trying out different combinations of molexes to power the graphics card, that should have resulted in both rails being used and therefore no problems...

As to recommendations, to my mind there are only a handful in that price range worth considering (given in no particular order).

The 500w Silverstone Element Plus - I don't know why it isn't mentioned more often since it's a fantastic unit.

The 500w Antec Earthwatts - The over current protection is non-existent so while it is labelled as having 2 rails, in reality there is only 1.

And last but not least, the 450w Corsair VX - Ideally you would want the 550w version since it offers the extra 8-pin pci-express connector + 8A more juice on the 12v rail (and it should slot between the vx450 and hx520 in price, so between £45 and £65), but sadly both models are so new that I can't find anywhere with the 550w model even listed and the 450w model is out of stock.
 
Well the Corsair HX behaves in exactly the same way as the Earthwatts...as do most 'multi-rail' units built by Seasonic. When I say OCP isn't there I guess I was making things too simplistic.

Let's take the HX as an example. It is specced as having 3 12v rails individually rated for 18A each, or 40A combined. Now I think jonnyguru applied 30A to a single one of those rails, and it didn't trip the power supply, therefore OCP isn't set at the 18A they specify. Had he gone on to test higher values, the unit would no doubt have kept working right up to the 40A mark, but if he tried to take it above that then the unit would finally trip itself.

So for the end-user the unit behaves, to all intents and purposes, like a single rail psu.

edit - Oh and of course it is a fantastic choice.
 
What I don't quite get is the relationship between the rails and the physical connectors. Take the noisetaker - it has 3 sets of leads coming out of the PSU with 2-3 moles connectors on each, and it then has an additional molex which is part of the 4-pin 12V lead and is labelled 'extra'. Is the 4-pin and 'extra' molex fed by one rail and the other 3 sets of molexes fed by the other? Or do the rails combine internally?

In theory I don't really mind whether the rails work effectively as a single rail, as long as the PC comes on and stays on :) I look at the Antec though and the specs say 12V1 - 17A, 12V2 - 17A and it reminds me of the noisetaker, which as you know bizarrely won't power my system. I wonder if the noisetake is just plain faulty, like one of the rails was dead when I bought it.

I'll probably go with the Corsair just because it's modular. I hate tons of unnecessary wires. Don't suppose either is especially noisy cause that's something else I'm not keen on.

Thanks again :)
 
That's possible (the noisetaker being faulty) since there is a guy in the graphics forum who can't get his Antec Truepower Quattro to properly power an 8800gtx of his, even though it should be more than capable.

As to how the cabling works out in respect to the different rails. You really need to pop the hood off your unit and see where they terminate on the PCB. That's something I've never been confident enough to do myself (safety aside it also voids your warranty), although I might give it a try with a Tagan unit I've just put out of service.

Safe to say though, unless they explicitly tell you (and in some cases like Seasonic, even if they explicitly tell you...), it's not something you can figure out just by looking at the exterior cabling.
 
Yeah I read about that 850W not power that guys GTX, but his 600W powering it just fine (or something along those lines). Very odd.

Anyway, I've ordered the Corsair HX 520W. Cheers for the help :cool:
 
Is this sort of problem why Tagan PSU's have a switch to allow you to either have dual rails, or a single one?

Must admit that the manual that came with the PSU, is a little vague as to what is actually on each rail.
 
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