Battery longevity with AC power inverter draw @ 175W

[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)

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?

Also do I really need a true sine wave inverter or will a regular modified sine wave inverter power a desktop computer?

Any additional information anyone has on the subject of portable power or building a portable computer/laptop please inform me or give me a link.

Thank You

 

[thecontinuum]

Sorry for the totaly "lamens" question I am marine biologyst electical engeneering is only a hobby. I have done more work and some of the basic calculations myself but I still need help with the DC power supply I am working on. You can find more specifics on the project in the "Computer engineering other topics" forum under a post "Building a battery operated portable computer..."

I would apreciate any help anyone could offer.

Have a happy new year!!!

 

[IRstuff]

The amp-hour rating of a battery is the product of current and the number of hours the battery can provide that current. Therefore, a 12 amp-hr battery will supply 12 amps for 1 hour, at which time, a battery that meets specification will have its output voltage will drop below specification limit

Under the above conditions, the battery provides V*I=12V*12A=144 watts for 1 hour. If your computer really draws 175 watts, you're going to be disappointed. On the other hand, if your laptop?? draws a more reasonable 60 watts or so, you'll get close to a couple of hours.

Have you thought about running the laptop directly off the battery? The inverter/converter combination will suck about 30% of your battery capacity.

TTFN

 

[jbartos]

Suggestions to thecontinuum (Marine/Ocean) Dec 28, 2002 marked ///\\\:
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)
///What you really are looking for is a DC to AC converter. There are plenty of them on the market.
Visit:

http://www.thomasregister.com

and type Converters: DC-AC under Product or Service which will return 50 companies to inquire about 150W DC-AC inverter (generally, converter) with 12VDC input.\\
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?
///It will run for:
time=12A-hr/(175Watts/12VDC)=0.82hours,
actually, it will be less since 175Watts is the inverter output. Normally, the inverter input may be 200Watts, depending on its efficiency. Then, the time=0.72hours.\\Also do I really need a true sine wave inverter or will a regular modified sine wave inverter power a desktop computer?
///If the inverter output voltage meets 5% of the Total Harmonic Distortion (THD).\\Any additional information anyone has on the subject of portable power or building a portable computer/laptop please inform me or give me a link.
///Try to surf web using proper terminology, e.g. converter or inverter, DC-AC, Battery, Charge, Capacity, etc. Visit

http://www.powerstream.com/in3s.htm

etc. for more info and pictures\\

 

[thecontinuum]

I have done much of what you suggested already in fact I have come to the conclusion that a DC to DC power supply is what I am really after. Here is a link to that page in the computer engineering section as it has my current calculations and full design plans (I am not sure if the link will work so if not get there the way I mentiond before)

thread233-40406 I wish I could edit the original thread to reflect my current situation but this link will give you the full details of my project

 

[IRstuff]

The basic issue is that you want to use a desktop motherboard in a portable application. Since everything is burning about double what a good laptop uses, your run times are going to be no better than 1/2 of the comparable run time for any of the rechargeable sources contemplated. Your approach cannot take advantage of the lower power devices found in laptops, so you're stuck.

Moreover, your cost figures in your original post suggests that your efforts could be directed to finding a good laptop for under $1000: Compusa shows an HP Presario for $849:

http://www.compusa.com/products/products.asp?id=334&category_id=334&srch_type=catg2#

Buy a couple of spare batteries and save yourself the aggravation, since there's no way you can package what you want into the same volume as a Presario+3 spare batteries.

Although the total cost will be higher, the utility increase, volume decrease and time saved might be worth the effort.

TTFN