Battery solution for a portable computer

[yellowcouch]

Hey all!
I am currently working on a project and have been given the task of figuring out the best way to power a computer from batteries. This is not my field of expertise and so I am struggling a little bit on the best option for the project. I am trying to power the computer in third world applications and so the solution would have to withstand some hot and humid environments as well as being portable. The total power consumption for the device is 46.725W at 12v (this is worst case sceneraio) and I am wanting to power the device for 13 hours. I have found a product that puts out 12v at 21,000 mAh and if I have done the conversion right then that means it is at 252Wh. Which I believe means I can run my device for about 5 hours off of that product, I think I am looking for something that is rated at 611Wh, but I could be wrong as I am new to these kinds of systems. I could really use some help because I do not know whats out there for me and I am uncertain of my formulas and math.
Thanks!

 

[itsmoked]

The found product is indeed:
21Ah x 12V = 252Wh. Of course that's if you don't draw above some specified reasonable rate.

46.725W / 12v = 3.9A is your laptop draw.

Too bad you can't just pick a laptop with a long running time. 7~8 hours is often possible. Then you bring two or three spare charged batteries with you and you have a good 20 hours of cordless available.

Paying close attention to your computer energy setting also makes a big difference. My laptop runs about 5 hours and if I drop the brightness down just one measly step of the 7 available it adds an hour to my run time. It would pay you dividends to mess with your settings to learn what the minimum settings are that allow you to work adequately.

Other possibilities would be to use some sort of fuel cell supply:

http://www.horizonfuelcellstore.com/store_us.html

Or get a standard deep cycle lead acid battery $40 to $90 a small inverter $50 and a charger $20 (Batteryminder) and/or a solar panel with a 12V charge ~ $150 and you're set for indefinite field power.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[IRstuff]

Or, look at what's currently available in high battery life products like:

http://www.apple.com/macbook-air/specs.html

Your design is a GIGANTIC power hog; the MacBookAir is running something like 4.5 W, only 10% of your design spec. Even if you could find a battery to meet your requirements, your user would still need to charge the battery, which would be extremely difficult to do with the standard of power in developing countries. The MacBookAir's power consumption is low enough that one could potentially recharge using a relatively small solar charger that could possibly even be shared amongst users.



TTFN
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[yellowcouch]

Thanks for the quick replies, it smoked I had thought about the lead acid batteries but I am concerned with the weight but the multiple laptop batteries might not be a bad idea. IRstuff unfortunately I do not have the same talent and budget as apple therefore cannot create a solution to be their equal. Is there a way to auto detect different inputs ie solar, wind, lead acid, and NiMH and regulate their voltage so we can have sort of a pick your own power option?

 

[IRstuff]

I think you missed my point. Your computer itself is the problem, not the battery. You need to completely revamp the computer to minimize its power consumption. Apple uses no proprietary technology to reduce their power consumption. Unless you get the power consumption under control, you'll have an unusable system. The standard Li-ion laptop batteries are the generally the most efficient form of power storage, and my 85 Wh battery for my Dell weighs 1.2 lb. 600 Wh would require 10 such batteries, weighing 8.5 lb, which is the weight of a pretty heavy laptop already, so you're talking about doubling that weight. Note, because you're pulling so much current, the battery's Ah rating has to be decrease because you're pulling out so much power so quickly. Then, you'd need to find some means of recharging the battery; my guess is that you'll be lucky to get a 100 W recharging source, which means a minimum of about 12 hr to recharge the battery.

The same 85 Wh battery will run a 4.5 W computer for 19 hr. Ta Dum.

TTFN
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[yellowcouch]

This is where the biggest energy draw comes from

http://www.elotouch.com/Products/LCDs/1537L/default.asp

but I can't really find a better solution for our application... I could always go down in screen size but that wouldn't really be good for the application. The other constraint is that we are required to use a development platform that pulls 16W on its own everything else in the system is almost nothing. If I could find a better solution for the ir-touch screen then that would be good, but all my hunting is coming up with nothing much better. I guess i should have specified the constraints a little better in the original post.

 

[itsmoked]

I'm completely amazed someone would consider running something as obtuse as a large industrial touch screen out in the boonies on a battery. You should probably re-think this entire project... With power consumption as the leading design criteria.

Keith Cress
kcress -

http://www.flaminsystems.com