How many watts / amps needed? The end-all and be-all answer.

powergyoza · Post by **powergyoza** » Fri Feb 14, 2003 3:54 pm

I was going to originally post this in GamingGod's PSU sticky thread, but I though it deserved its own topic.

I've finally taken some power measurements using a Fluke 36 clamp-on ammeter. It lets me measure current draw of the components in my dualie system. Tell me if I measured this properly:

I fired up 2 copies of BurnK7 and put discs into both my CD & DVD. For good measure I also started file searches on both my hdds, but with BurnK7 running, the searches were at a standstill.
I wanted to measure each group of wires (3.3V - orange / 5V - red / 12V - yellow) with all these things going at once, but I couldn't make enough room for my ammeter to fit through all the wiring. Instead I measured each group of wires going to my mobo, hdds and CD/DVD separately.
Measurements are taken at peak
See signature below or my dualie article for system specs.

Results: (in order of 1] CD/DVD, 2] hdd's and 3] motherboard)

3.3V: 0A / 0A / 2.5A: total = 2.5 A / 8.25 watts
5V: 1A / 1A / 27A: total = 29 A / 145 watts
12V: 1.7A / 1A / 1.5A: total = 4.2 A / 50.4 watts

Total power consumption: 203.65 watts

A 300 watt PSU that does 30 A on the 5V line would be just enough for this setup. Add a modern GeForce or ATI card and I'd likely have a real need for a 400 watt PSU.

Post by **MikeC** » Fri Feb 14, 2003 4:16 pm

OK, powergyoza, you're gonna have to bring that thing over here & we can go crazy with measurements for an afternoon...

Post by **Rusty075** » Fri Feb 14, 2003 4:22 pm

Excellent work! And very useful too.

It reinforces a couple of things I've been thinking all along:

1: Most systems don't need anything bigger than a 300Watt power supply.
2: People need to start buying PSU's based on the amp ratings for the individual lines, not the total wattage.

GamingGod · Post by **GamingGod** » Sat Feb 15, 2003 3:56 am

yea i wont have 2 processors and 2 cd-roms, and 2 hardrives all working at once any time soon. Id have to get 1 more of each to do that

powergyoza · Post by **powergyoza** » Thu Feb 20, 2003 2:29 pm

digitalix wrote:no wonder amd usually recommends 300 watt PSUs or higher, they tax the 5V rail like crazy the cd drives or the hard drives mostly use up the 12v rail, looks like i'll have to reconsider amd procs in future purchases, hmm

Yeah, I was kinda disappointed with my setup too. My motherboard is a dinosaur in the SMP-Athlon world. I'm optimistic that all the recent ones from Tyan, Iwill, Asus, MSI, Chaintech and Gigabyte are more modern in terms of their power draw.

Tore · Post by **Tore** » Thu Feb 20, 2003 9:58 pm

MikeC wrote:OK, powergyoza, you're gonna have to bring that thing over here & we can go crazy with measurements for an afternoon...

That would be great! It's not very easy to find that information. Some units have information written on the labels (for instance, a 40GB Fujitsu HD label say "Rating 12V 0.4A 5V 0.5A"), but far from all components have the information so easily available. And even if they have, it might not be easy to find out before it is bought.

It is important information for large PCs, but maybe even more so for small computers. How much can you put inside a computer with 200W PSU with 3V 16.7A 5V 21A 12V 10A (13A peak)? Obviously not dual Athlons

but I've never seen a microATX or miniITX board with dual Athlons either

But seriously, the above mentioned data is one of the most powerfull microATX PSUs.

And what about the external 55W PSU used with many mini-ITX computers? I asked mini-itx.com, and they told me that they doubted it could run the EPIA ME6000, a 3.5" HD and a full sized CD-ROM, but I don't now if they had tested it or not.

A collection of data for at least some units would be very nice!

blakerwry · Post by **blakerwry** » Fri Mar 14, 2003 2:04 pm

digitalix wrote:no wonder amd usually recommends 300 watt PSUs or higher, they tax the 5V rail like crazy the cd drives or the hard drives mostly use up the 12v rail, looks like i'll have to reconsider amd procs in future purchases, hmm

really depends on the motherboard... some get their power from 3.3 and 5v and some also get power from the 12v lead (hence the new aux 12v connectors)
... even if it doesn't have the aux 12v connector I believe that some mobo's use the 12v lines in addition to the 5v..

I believe most DDR baords are using the 5v line to acchieve 2.5v for the RAM... SDR SDRAM operated at 3.3 volts, so I assume they took this directly from the PSU...

Tore wrote:I've never seen a microATX or miniITX board with dual Athlons either

There are alot of mini ATX dual boards actually... not sure what the distribution between Intel, AMD and others are.. but they actually are about as common as full ATX dually boards.

powergyoza · Post by **powergyoza** » Fri Mar 14, 2003 7:51 pm

blakerwry wrote:really depends on the motherboard... some get their power from 3.3 and 5v and some also get power from the 12v lead (hence the new aux 12v connectors) ... even if it doesn't have the aux 12v connector I believe that some mobo's use the 12v lines in addition to the 5v..

Although I can't prove it, I'm a little doubtful of any ATX 20-pin only mobo that draws any significant current from the 12v line. There's only 1 wire for 12V on the 20-pin ATX connector. Sure, it's rated to deliver 5 amps +, but would any mobo maker trust the CPU to 1 wire w/ no backup?

There are alot of mini ATX dual boards actually... not sure what the distribution between Intel, AMD and others are.. but they actually are about as common as full ATX dually boards.

Yeah, distribution must be 100% intel. I'm pretty up to speed with the Athlon dualie mobo's and ALL are ATX or larger.

Seal · Post by **Seal** » Sat Jul 24, 2004 11:59 am

great post! do you have a pic or url of that clamp on ammeter your talking about? i wanted to buy one of those "watt measuring" plugs like you see in hte spcr psu reviews but if the clamp on is anygood i might get that. In theory could you use the clampon over the psu's main kettle lead?

thegrommit · Post by **thegrommit** » Sat Jul 24, 2004 4:04 pm

Isn't this out of date now? I was under the impression Athlon 64's (and P4's) draw heavily from the 12V rail.

sthayashi · Post by **sthayashi** » Sun Jul 25, 2004 1:48 pm

Seal wrote:great post! do you have a pic or url of that clamp on ammeter your talking about? i wanted to buy one of those "watt measuring" plugs like you see in hte spcr psu reviews but if the clamp on is anygood i might get that. In theory could you use the clampon over the psu's main kettle lead?

They look like this:
http://www.fluke.com/products/sections.asp?AGID=6&SID=5

larrymoencurly · Post by **larrymoencurly** » Sun Jul 25, 2004 11:18 pm

The cheapest DC clamp-on I've seen was a Sears brand for under $50, but it didn't give RMS AC readings. A DC clamp-on probe alone can sometimes be found for $35-40 from www.mcmelectronics.com, but it's not auto-zeroing.

sthayashi · Post by **sthayashi** » Thu Sep 16, 2004 11:48 am

Just found a couple Clamp meters that aren't too outrageous in price.

The UEi DL49 and DL99 can be found online for $100 and $150 respectively and they both appear to be able to measure DC current. When I feel like I can afford to get one, I will report back on results.