Voltage/Current Rqmts for ASUS A7V8X


Jan 4, 2003
I am building up a new system, utilizing an ASUS A7V8X motherboard. This is the full blown version, with all the features available (ASUS p/n 90-M7A610-W0UAY, described on the box as A7V8X/GBL/1394/SATA/R133-UAY).

An Athlon XP2100+ processor is installed, with a Dynatron heat sink/fan combination for cooling. The board has 512MB of Samsung DDR memeory installed.

I am planning to also install an MSI G4Ti4200 (64MB) graphics card, a Western Digital WD400JB hard drive, an AOpen CDRW4850 CD writer and an AOpen CD956E CD reader. The remaining devices are the usual case fans, keyboard, mouse, 3.5" floppy, et cetera.

I have a copy of a technical paper authored by ASUS (document # 26003A, dated May 2002), which provides an excellent procedure for calculating system power consumption. Following this procedure, in order to properly select a power supply it is necessary to be familiar with the voltage/current requirements of each of the components in the system, per each of the available voltage rails (i.e., +3.3V, +5V, +12V, -12V, and +5VSB).

So far, I have determined, with reasonable assurance, the voltage/current values for most of the components in my system. Unfortunately, I have not been able to nail down this data for the A7V8X motherboard (or the CD956E CD reader, for that matter). The manual for the motherboard indicates the +12V rail should be able to provide a minimum of 8 Amperes, but this may be so as to ensure the Athlon processor has sufficient current. I say this because in checking several AMD websites and data sources, it appears the XP2100+ processor requires 7.49 Amperes on the +12V rail. The manual also says the +5VSB should be able to provide a minimum of 1 Ampere. This leaves me with no knowledge of the actual motherboard requirement for +3.3V, +5V, +12V, and -12V rails (assuming the +5VSB really needs a full 1 Ampere).

I noticed this website seems to have excellent technical reviews and articles concerning a great many hardware issues. In fact, I believe this is the ONLY website that actually has a review that explores the claims and capabilities (or lack thereof) of currently available PC power supplies.

So, I have come here in search of the data I need. Perhaps someone on the forum knows the answers, or can at least vector me to a location wherein I can obtain the data on my own. I have already requested this data from the vendors, and am still waiting (2 days, now).

Thanx in advance to anyone who can provide assistance with this problem.

Bob Scully


Feb 3, 2003
I can sympathize thoroughly having been through a similar experience.

Bob, it sounds like you hit the same mobo industry stonewall as I have. They just won't tell you their power consumption numbers (with the exception of Intel who print everything!)

I emailed one mobo manufacturer asking specifically for a particular model's power consumption at each of the supply voltage levels. I received an email response saying there are many other factors contributing to power consumption such as hard drives, CD/DVD, processor, memory, and etc. (Duh!) It concluded by saying a nice 350W supply should be sufficient. This was after I had explained I was designing an all-in-one system that will have no PCI or AGP cards at all (built-in video, audio, LAN on the mobo, don't need modem) and only one HDD, FDD, and CDRW!

I tried a different tack with another mobo company and phoned their US tech support twice. In the two conversations I managed to discover that "the engineers absolutely won't give out those numbers." Instead, they advise their customers to allow at least 10% additional power over the sum of the loads of all the other system devices added together.

Is it any wonder there are quite a few of us wandering the newsgroups, online communities and other 'Net resources lantern in hand like Diogenes looking for a motherboard company engineer willing to tell us the truth? Do they think we aren't smart enough to add up some numbers and come to a sensible decision?

Since you already have AMD's "Builders Guide for Desktop/Tower Systems" I would suggest you try estimating using the sample numbers you find in the tables on pages 7 and 8 where you don't have anything specific from the device specs. After doing some digging, I suspect the white paper numbers are probably close enough for estimating purposes.

Consider this while reviewing the example power budget on page 7 of the AMD guide: Shuttle has come out with a line of cute little cube computer barebones systems such as the SS40 that support Athlon XP and P4 CPUs, a gig or two of DDR memory, Firewire and USB-2 ports, and a couple of PCI and/or AGP slots too. They come with 200W power supplies with 12V rails at 10 Amps. Either I want to get my hands on a whole bunch of those magical power supplies or some of us have been misled about power consumption! The AMD numbers are actually generous.

I hope that Tom's Hardware Guide and other groups like it will speak up on behalf of DIY builders and demand that the mobo companies and other PC parts vendors start publishing adequate power consumption data for their products.

Good luck.;)

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