Thread: Rail power usage

I am not sure about the Mobo and CPU usage, but the Lilliput, HD, DVD-ROM all have label on what the power consumption is. Keyboard, NIC are 5V and RAM is on 3.3V (I think).
For example Lilliupt use 12V at 0.9A (I think). DVD-ROM and HD use both 5V and 12V. Typical DVD-ROM use about 1.5A on 5V and 0.5A on 12V.

You will be fine with the opus 90W, but I would advice you to get the most powerfull PSU you can afford. The reason is that down the road, you will not be happy with a P2 400MHz performance if you do any video/DVD playing in that setup. Once you decided to upgrade, that powerfull PSU is handy instead of buying a more powerfull PSU and sell the less powerfull one.

Originally Posted by tigergibb

Hi, I've done some searching and reading and am working on a setup for my CarPC. I would like to know fairly close to the amount of power I will be drawing. If anyone has any corrections to this, or can help me fill in the blanks, it would be great. Thanks.

Check Power[/AUTOLINK] requirements"here for processor power supply requirements. It seems to be the reference site of choice around here.

Originally Posted by MatrixPC

I am not sure about the Mobo and CPU usage, but the Lilliput, HD, DVD-ROM all have label on what the power consumption is. Keyboard, NIC are 5V and RAM is on 3.3V (I think)

Matrix, are the motherboard and all cards (AGP and PCI) typically run from the 5V+ rail?

Originally Posted by parksgm

Matrix, are the motherboard and all cards (AGP and PCI) typically run from the 5V+ rail?

It's depend on the mobo/cpu generation, but most of them are run on 5V rail. For this particular setup, I am sure it is.
For sure, today desktop cpu, video card are running on 12V rail.

Originally Posted by MatrixPC

For sure, today desktop cpu, video card are running on 12V rail.

Allirght, what dou you know about a 1.7 ghz P4 on a dell MB with AGP card?

Originally Posted by parksgm

Matrix, are the motherboard and all cards (AGP and PCI) typically run from the 5V+ rail?

Motherboards pull some 12v and some 5v, although I believe it's primarily 5v.

The PCI bus uses 3.3v.

Originally Posted by DarquePervert

Motherboards pull some 12v and some 5v, although I believe it's primarily 5v.

The PCI bus uses 3.3v.

Great...thanks for the info. Sounds like it's difficult to overload the PCI bus, which seems to an arguement for using a PCI based graphics card vs. AGP, as it would distribute the load more evenly.

The motherboard is another matter...there seems to be no way to determine the MB requirements other than the typical 25-45 watt estimate, and if power is drawn from both the 12V and 5V rails, how would I know if I would exceed my PSUs rating?

Okay, found some additional info that will help both my and the OP's situation, so I'll post it here:

Graphic card power requirements for specifc cards can be found here. In summary, So, PCI graphic cards use power from the PCI bus, which is 3.3v (a seperate rail on the PSU), while AGP derive the majority of their power from the 3.3V and 5V rails, with only 1A or so from the 12V rail. I don't know why it didn't occur to me to look at the AGP and PCI standards for specs before now!

I've quoted the relevant info from the site above:

The PCI-Express standard allows between 60W and 75w to a graphics card through the PCI-E slot itself, without the need for an additional power connector. But with more and more graphics cards coming out that require either a Molex or 6-pin PCI-E power adapter, this is a dead give away that a PCI-E card needs more than 75W to operate stably (7800GT for example). Each 6-pin PCI-E connector can provide another 75W . So a PCI-E GFX card with a 6-pin power connector attached can draw up to 150W max, with a dual card setup they can draw up to 300W max between them both.

The AGP 3.0 standard (AGP 8x) can only deliver a maximum of 41.8 W (6A from 3.3V, 2A from 5V, 1A from 12V = 41.8W and an additional 1.24W could come from the 3.3V auxiliary at 0.375A). AGP cards that need an extra power input will have a molex power connector (9800 Pro for example). By adding the four-pin Molex connections, manufacturers extended the life of AGP cards as each supplied 6.5A or 110.5W from these right angle connections (12V + 5V or 17V x 6.5A = 110.5W). Which makes a total of 151.8W available to AGP cards with a single molex connector.