Building a battery operated portable computer...

[thecontinuum]

I was wondering if anyone out there could show me how to solve this problem. Basically I am contimplating making a portable computer that I want to power with a battery and an AC power inverter (I couldnt find a 150W power supply that accepts 12v DC - only 120v AC so I have to use an inverter) I did however come across a 12v DC ATX computer power supply but the lowest wattage I could find was 250 watts which is way more than I need.

How long will the computer run if it is using 175 watts @ 120 volt AC inverted from a 12 volt DC 12 amp hour battery. How long would it run if it were drawing off a 12 volt 32 amp hour battery?

Here are the specs i am contimplating for this project:

10.3 Watt Solar Panel 0.62A @ 16.5V $155.00 - 3.6 lbs

12 V AGM 12 AMP HOUR Battery $ 43.00 - 9.0 lbs
or
12 v AGM 7 AMP HOUR Battery $ 27.00 - 5.5 lbs

VIA EPIA M9000 Mini-ITX 90W (on board 933Mhz CPU, Video, Lan, Audio...) $140.00 - ??

Maxtor 120GB About 10W Max $146.00 - 1.27 lbs

Kingston 512mb PC 2100 4.4W $118.00 - 0.2 lbs

Viewsonic VX500+ 15in LCD Monitor 330NIT - 550:1 Contrast Ratio - 25W $407.50 - 8.6 lbs
(Removing the case and stand should make it much lighter)

12 Volt DC ATX 150 Watt Power Supply ??? - ???

Here is a review of the mini-ITX motherboard w/ CPU

http://www.tweaknews.net/reviews/viaepiam9000/

The main application is Video Capture & Still Photo Storage from Sony DSC-F717 Digital Still Camera. It will need to fit into a rather small pelican case and be fully mobile. Second it will be used for GPS maping software. It must be light enough to be backpacked into remote areas but have enough power in its batteries for at least 8hrs of usage between recharges.

It could also be used for MP3 & DVD playback not to mention console games

 

[maelstrom]

I can't answer all of the details for this, but you would probably do pretty well with the 250W power supply. It will only supply as much power as needed, it won't supply 250W if you only have a 2W draw on it...

Also, you'd probably do better to find somebody selling a laptop cheap. Trying to cut everything down for a home-brew portable system is going to be a pain. (but hey, i am building a liquid-cooled PC, so who am I to talk?)

 

[thecontinuum]

One thing that I don't understand is how much of a draw (in amps) the system is actually going to place on the battery. I am confused as to when they say "minimum 90 watt power supply required" is that 90 watts at 120 volts AC or 12 volts DC? And does that 90 watts include the entire system (mobo, cpu, ram, Hard disk, etc.). The monitor uses 25 watts @ 120 volts AC which will have to use an inverter - what is that going to drain out of a 12 volt battery in amps?

I have asked a similar question in the electrical engineering forum but I don't think anyone is going to answer the question because most of the topics in there are way over my head and my question is laughably simple...to an electrical engineer...

 

[richs]

Hi-

I don't think that anybody can easily give you a "correct"
answer. Please note that specifications are apt to be
a tad on the conservative side. However the
90Watts of power that a card would require is the
amount of power required by each of the voltages for
the card (typically +5V, +-12). The 90 Watts is used
for a cooling specification. I would not use just the
90 Watts for specifiying a power supply. Different
designs have different max ratings for different supplying
voltages. You have to check on a voltage by voltage
basis.

When rolling out a hardware design and specifying
typical and maximum power consumption for a card,
I use the IC's data for the information (digital cards).
I take the typical as the average for the IC (the IC guys
have measured hundreds of ICs for the typical and max
power consumed). I take the max as a 3 sigma (3
standard deviation for the IC). I then calculate the
average (typical) and the 3 sigma for the collection of
the IC's for the max of the card. This, I believe is standard
practice. This doesn't take into account power resistors
that are drawing a lot of wattage.Analog designs
sometimes require this, not so much in the digital area.

For systems design, you do the same thing with each
of the boards, plus the loss to heat in the power supply.
Your thermal loading is then a "rough guess" as to how
much heat dissapation the system has to shed. Then
typical engineering practice takes over. You do a
prototype and stick a bunch of thermocouples at selected
spots, and dink with the design to get it right, cross your
fingers and hope that you don't have too many down
systems............

Please note that the battery condition will degrade over
time, providing less power holding capacity, greatly
affecting battery life.

Just going over the numbers, and I could be quite
wrong, let's look at your battery. It is a 12 volt, 12 amp
hour battery. I assume that it would supply 12 volts,
at one amp for twelve hours. Or, it could supply
12 volts at 12 amps for one hour. That kinda works out
so that it would (theoretically) supply 144 Watts for one
hour........ Doing a simple add of the power requirements
for your system, it looks like right around 125 Watts,
give or take. Assuming a really, really, good inverter,
of say 80% and a really really good power supply
efficiency of 90%, I think (note the word, think) that you
would expect to get less than one hour of work out
of the system with a 12AH battery.

I would concur with maelstrom, that a laptop would be
a good approach for the system that you have in mind.

Many laptops have cables that connect to a car battery
and they are specifically designed to conserve battery
power. Otherwise, you might look at the "Eurobrick"
as an alternative.

Please note that your solar panel will not allow the
system to operate more than one hour per several
days of charging, so your criteria of

>backpacked into remote areas but have enough power
>in its batteries for at least 8hrs of
>usage between recharges.

Is not likely to happen with anything larger than a pda
of some sort. Sorry 'bout that.

Hope that this information helps.

Cheers,

Rich S.

 

[thecontinuum]

I have come across actual plans for a 8-17V DC power supply (PCB board diagrams I can use to etch and build from scratch) It measures 142mm x 46mm (height would be determined by the size of heat sink I choose) and weighs under half a KG (also dependent on heatsink) It is extreamly efficient (over 80% @ full load)

It will supply:

5V at 10A* (13A peak)
12V at 1.3A
-12V at 100mA
-5V at 100mA
*3.3V at 5A (6.5A peak)

* If the 3.3V option is used then only 5A is available at 5V.

This should be enough power but until I can find the exact usage I am not sure if 5A @ 5V is going to be enough for the M9000 & a 120GB 7200rpm HD (860mah max @ 5v). If it isn't enough I could make a seperate PCB to supply 3.3v @ 5 Amps. Will the system run without the 3.3v?

Some motherboards require a delayed Power Good signal before they will startup and this power supply doesn't include that feature in these plans. I am not sure if the VIA EPIA M 9000 will startup without it.

It is near impossible to find any specifics on the energy consumption that the EPIA M 9000 actually uses (Amps @ 12v, 5v, 3.3v, -12v, -5v) if anyone is able to find this info please let me know.

The total cost for all parts & blank PCB board is under $40 US

Here are is all the info I have come up with so far:

Estimated cost anaylisis and breakdown of project & energy consumption in AMPS at 12v DC (to estimate battery drain - not an indication of actual 12v, 5v, &3.3v power requierments):

Maxtor 120GB ATA 133 7200 RPM HD w/ FDB $146.00 - 1.27 lbs
Seek: 1.0195A Idle: 0.613A Standby: 0.0745A

Kingston 512mb PC 2100 $118.00 - 0.2 lbs
0.37A

Viewsonic VX500+ 15in LCD Monitor $407.50 - 8.6 lbs
(removal from case and stand shold get it down to under 3lbs) 25w @ 120v AC = 2.09A but with the power loss to inverter < 2.4A

VIA EPIA-M9000 $140.00 - ?.? lbs
?.?A (min req. for psu for entire system is 90 watts)

--NOTE-- I found the specific power requierments for a similar SBC system (Intel Pentium3 933MHz CPU with 256MB SDRAM) but acording to VIA the EPIA series uses less power due to the C3 Processor.
I calculated the total draw at 12v = 3.71 Amps


Battery Supply Options:

Lithium Ion Batteries:

20 x 7.4v 1500mah batteries soldered in series and paralell to make:

1 x 12v 18 AMP Battery $259.60 - 4.01 lbs


NiMH Batteries:

20 x D Cell 9000mah batteries soldered in series and parralell to make:

1 x 12v 18 AMP Battery $156.00 - 7.28 lbs


AGM BAtteries:

12v - 18 AMP Battery $ 53.00 - 14.0 lbs


Based on current estimates (not exact by any means but getting close) each 18 Amps of battery power should power the computer & monitor (fully running not idle) for 2.5 to 3 hrs. This is a conservitive estimate in practice we may get more.

Obviously the lithum ion batteries are light enough that you could easily cary enough for upwards of 9 or more hours of computing time which beats any laptop manufactured to date and is still less expensive than equivilent bateries for said laptops.

 

[cbarn24050]

Hi, there are lots of supplies that will do all that, you do not want to transfom up to 110v only to transform back down to 5v.

 

[thecontinuum]

As I stated in the post right before yours, I have chosen to go with building a 12 DC to 5v, 3.3v, 12v, etc. regulated ATX power supply. I simply need to know the specific power requierments of the motherboard.

With my current designs I have gotten the weight without battery to 3 to 5 lbs. Which rivals laptops and I would like to point out that this is not a full size motherboard and uses less than 30% of the power used by a normal ATX board. I doubt that laptops use much less power - the LCDs they use use less power but are usually to dim to be viewed in full daylight.

Without battery pack and LCD the base unit will measure 18cm x 18cm x < 7cm.

I am currently considering using a less powerful and smaller 5.6 or 7&quot; NTSC LCD TFT screen that will use < 7W @ 12v DC. It costs $129 but I don't believe it is sunlight readable. I am not sure if the resolution will be high enough to use GPS mapping software but it would increase the battery longevity to 4 hrs or more (on a single 18 Amp battery)

I have also considered using the 5.6&quot; LCD and the 15&quot; LCD both - using the 15&quot; only when nessisary for mapping or when a car or wall outlet are available. Using the 5.6&quot; when runnig off the batteries.

 

[jessemikah]

first of all all lcd monitors are 12volt inside. some will have the converter inside them and others will convert to 12v for input. Second can you email me that power supply design that you have for the 12v dc atx psu and where you are seeing the via m 9000 for $140? jessemikah@hotmail.com
I have a guy who is designing a 90watt psu for itx boards for 12v apps. and has a 150w at the moment but he wants $150 each. The only drag is that his psu's will turn the computer on and off with the ignition. Please help me if you can and I will try to do the same with you.

Jesse

 

[IRstuff]

A couple of comments

>ATX motherboard dissipation not withstanding, a low-power laptop can run 3 hours on a batteries rated for less than 70W-hr, partly due to the specific design of the laptop motherboard being able to shut down power as required. Since your motherboard requires 90W, you would need the equivalent of 3 laptop batteries to power it for the same duration. I would recommend cannibalizing a laptop over using a desktop motherboard. Particularly in light of the need to gin up a power supply and converter for the motherboard, a laptop has the converter built into its motherboard.

>While laptop displays are not daylight readable, neither are desktop. Our company builds daylight readable LCD displays for military, and they would run less than an hour on laptop batteries even without the PC. Your best bet is to find a reflective LCD display, possibly ditch color for monochrome. Why try to fight the sun? This would allow you to only have to use the backlight at night, thus conserving battery capacity.

TTFN

 

[ElectroKing]

Scenario one with 12 vdc and 12 amps is not recomnended. 12vdc 32 amp will give you close to two hours of continues operation assuming you are working in the dark!

Enjoy

 

[ceh4702]

I purchased a 60 watt power supply and it was powerful enough to run just the PC component from a company called I-Tuner. I was able to power the Motherboard, Hard Drive, and CDROM (Standard Size). This device is a DC to DC power supply which I plugged into a AC 110 to 12V DC converter (55 watt). This might work off a car battery.

I have been looking at things that work with a car and a while back I found some sites that sell smaller LCD screens that may pull less power. They ranged from size of 4&quot; to 14&quot; at differnt locations. Some of these were designed to be mounted in a vehicle for viewing videos or TV. Some could be mounted in the roof and be folded out to view. So look for LCD monitor designed for a vehicle. I think a small 4&quot;-8&quot; screen would pull a lot less power.

However, I built my little computer from a VIA EPIA 800 Mhz C3 model MINI-ITX motherboard. This is probably the model with the most bang for the watt.

I saw that Linksys was selling a small 110 inverter that plugs into a cigarette lighter. For more information on power consumption you might try looking at a site that is in the US called:

http://www.homepower.com

This is a site that specializes in Solar Power. If you had a portable solar power system you might be able to run off of a 1 or 2 battery system with just one 60-80 Watt panel. If you could charge and run the computer at the same time, you might be able to extend the time you can power the computer. Another option might be a small gas powered generator.

 

[raudy]

i have read the answers to the topic and had a something
to add has anyone seen the mini computers at

http://www.xenarc.com

seems to me they are running a laptop motherboard does anyone know were you can buy new laptop motherboard?

 

[IRstuff]

Have you tried a websearch?

http://search.dogpile.com/texis/search?q=laptop+motherboard&cat=web&top=1

TTFN