Are PSU calculators any good?

Shrub

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I've just bought a Dell Optiplex P2-350 mobo. I comes with a CDROM drive, floppy, integrated GPU and SPU and a 145W PSU and 1 stick of 64MB PC100
According the various calculators this set up is pushing the 145W supply to the limits, but, I have another machine that came with only a 100W PSU with the following specs:
Compaq Deskpro P3-650, Matrox Millennium AGP 450, CDROM drive, floppy, SB128 PCI soundcard, 128 MB stick of PC125. I didn't realise initially that it was only a 100W PSU and I installed a ti4200 card - and everything worked fine.

I'm presuming now that these calculators are only any good for high end machines, so what are the true PSU requirements for my Optiplex?

Thanks
 

fishmahn

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The calculators are only guesstimates. They say a CD burner (for example) uses 'X' watts, and some do, but others use less. Most of them assume the max power of all brands in the class. Plus that 'x' watts is the max the device will use. Most of the time it uses less.

Its a good tool to determine what capacity PSU to buy, but that's all it is - its not exact by any means.

Also, most PSUs are crap. A crappy 400w PSU might be able to put out 400w for an hour, but for longevity, it can only put out 300w, and with some even that is pushing its limits.

The PSU in Dell and Compaq systems are probably rated at continuous output (I know from reliable sources that Dells are), while most other PSUs are rated at max output, and continuous output is only 75% of that (if that much).

That old DELL probably doesn't overload the PSU. If you were to add 3 more HDDs and a DVD burner, it would likely still be adequate (though maybe straining), a high-powered video card (not a 4200, but a 6800) would probably push it over the edge (but that would be a waste in a 350mhz system anyways). If you were going to buy a new PSU, I'd suggest a high-quality 250watt, or if you want a cheap one, 400w+, but that'd likely cost as much as the good 250w.

My father had an old Packard-Bell (386sx) that came with a 73w PSU (I think it was 73 - under 100 for sure). When I was putting together systems, I insisted on a 250w for the same class of system because PSUs you buy at the store are not nearly as good as the ones put into the pre-builts (that has changed, but you have to be careful because there's still a lot of crap out there)

Mike.

<font color=blue>Outside of a dog, a book is man's best friend. Inside the dog its too dark to read.
-- Groucho Marx</font color=blue>
 

Shrub

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I have a spare 380W PSU, Tagan with the irritating clicking voltage regulator, which I could use outside the case. Proper Dell GX1 low-profile PSUs seem to be very rare and I haven't seen any "3rd" party ones that'll fit.

I don't think I'd need a new PSU anyway. Replacing the HDD and CDROM with newer drives and adding a cheap S-vid card is not going to cause brownouts.


Thanks
A 6800 on a P2 board sounds like a fun idea. To me it seems like the way graphics card have more transistors than CPUs these days - maybe they should just stop making motherboards and instead build giant graphics boards with a PCI/AGP type slot for a CPU :D
 

Shrub

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Actually I don't think I can use the Tagan directly. The Dell PSU seems to be proprietry - the mother board connector looks like a normal ATX type, but there's a second one with 5 lines, from what I remember. The PSU also has "ATC" or "ATE" stamped on it. I can't remember precisely but I'll check inside again later, I can't find any reference to an ATC or ATE PSU on the web though
 

fishmahn

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This sounds like one from the time when Dell used proprietary pin-outs for the mobo connectors. No idea where you'd find a replacement though.

Mike.

<font color=blue>Outside of a dog, a book is man's best friend. Inside the dog its too dark to read.
-- Groucho Marx</font color=blue>
 

Shrub

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Thanks. I've found an adaptor cable to get normal PSUs working on Dell machines so I can use my dodgy Tagan - they're about 20 quid though, I probably should try to make my own. Don't you just hate proprietary components on PCs and consoles :/