computer power usage

[khbritten]

Hi, everyone, it's been a while. I am trying to decide on a boat computer, largely for nav purposes. We are trying to run a low-power boat for offshore passages, and want to install the most amp-stingy computer. I am thinking either a Mac Mini or a fanless ITX computer, run directly from the 12V using a DC-DC converter might be the most efficient and durable system. Does anyone have any real-world experience with how much current either of these types of computers would draw in use? Other thoughts on the choice or setup?

thanks!

Ken

[btrayfors]

Ken,

You might want to check out the new MacBook Air: http://www.apple.com/macbookair/

They're not showing actual power draw, but with a 45W power adapter it probably draws less than 4 amps @ 12VDC.

Bill

[brak]

I tested a few standard laptops (an ACER, a Dell and PowerBook) - all came with adapters of 60-80W. Presumably maximal draw of such adapter would be about 5-7 amp. However, I found that under most conditions they would only draw 2-4 amp. Power usage of a computer is a complex function and it depends greatly on how you use the computer. Monitor and processor are two most power hungry elements. Intensive processing and bright monitor settings (and, to a lesser degree, lots of video processing if you have a fairly powerful video CPU, though this is rare in laptops) will probably increase power draw.
Incidentally, I doubt that macbookair is significantly less power hungry than any other light laptop - and it is certainly way too expensive for its capabilities. But that is a whole another religious debate

[khbritten]

I am trying to stay away from laptops because they are likely to take a beating, both from their moving parts and from heat. We'll have one or two on the boat for backup, but I want a permanently mounted unit. Some numbers I have gotten from manufacturers so far are well less than the wattage of the supply, naturally. Some of you might be interested in the one quite detailed estimate I got from AR Engineering, which puts together quite fancy boat systems:

The HDD's all use about the same amount of power, 1.1 amps on spinup
(13watts for less than .5 sec)
2 watts on read and seek, .86 watts on idle and .26 watts on standby.
The processors vary on just how busy they are, if your only using typically
30% of capacity they pull about 5 watts. Thermal design specs for the Access
processor at max capacity is 15 watts, about the same for the Reliant Duo,
and 21 watts for the Reliant. They almost never use this much power running
marine type software. (and not continuously)
The Access has a fan that runs at varying speeds depending on the
temperature, typically 3 watts.
At room temp it just idles and power draw is much less.

But that's all theoretical, and theory will only take you so far...

[artbyjody]

Just a casual thought on this. A desktop is going to take the same beating - and they are not engineered for abuses (as most laptops are engineered to withstand shocks most desktops really are not (how many times is a desktop expected to just be dropped, kicked over or tossed on a couch etc).

This is the one case where heat is your friend. Moisture will kill electronics and your desktop will have far more air flow and therefore pull in more moisture over its lifetime. With a laptop - the constant heat will keep the electronics dryer in the long run and smaller vents when not in use limits amount of air being exposed. Also a laptop can just be tossed into a watertight bag when not used and will take up far less retail space and weight).

Just casual thoughts, if you had anything but a sailboat - maybe, but on a sailboat - I do not think a desktop will last long at all....

[brak]

I would be reluctant to put desktop system on a boat. Unlike laptops, desktop components are not built to be subject to constant motion. Desktop hard drives will definitely brickify after a while, other components may vary. Solid state disks might be the way to go but they are still relatively small and very expensive.

What the heck is Access and Reliant processors?

[sailingdog]

BTW, the MacBook Air is available with a solid state flash drive for a slight price premium.

[brak]

Originally Posted by sailingdog

BTW, the MacBook Air is available with a solid state flash drive for a slight price premium.

slight heh.

[sailingdog]

Picky picky picky... everything is relative... The MacBookAir can run BootCamp and be setup to boot in either Windows (XP or Vista) or Mac OS X.

BTW, the solid state drive is only 64 GB IIRC.

[labatt]

Definitely be careful on laptops... I got an HP with a big screen so we could also have it double as a family DVD player for when it rains out. The silly thing draws 10AH-12AH when it's charging and 7AH when it's not. I'm going to get a new laptop for when we cruise, and I'll be focusing on the 12inch screen units with slower processors (less heat consumption, lower power supply draw).