How long can I run my computer using an Inverter?

1. Mar 30, 2013

owen_a

Good Evening,

I have a 12V Car battery which supplies 85Amps. I have a 500W Inverter with a peak of 1000W. One of my computers which I want to run has a 200W power Supply. I would like to know how long I can power this for 12 hours and 24 hours. If the battery cannot power it for that long, then how many batteries would I need to power it for the time wanted? I don't mind creating a battery bank.

Thanks.

2. Mar 30, 2013

phinds

The stats you have provided are not adequate to answer the question you have asked. It is irrelevant how much power your computer power supply CAN provide (200W) but rather how much power DOES it supply.

Also your sentence "I would like to know how long I can power this for 12 hours and 24 hours." does not make any sense. 12 hours is 12 hours and 24 hours is 24 hours.

3. Mar 30, 2013

owen_a

Forgive me for the inadequate information provided. If you can tell me what you need from me in order for the calculations to be done, then I'll try and give you that information, however, I do not know anything else other than what I've said since I just got given the battery.

4. Mar 30, 2013

milesyoung

You could do a crude estimate if you knew the energy capacity of your battery, the minimum efficiencies of your inverter and computer power supply and how much power your computer will draw on average.

5. Mar 30, 2013

owen_a

A crude estimate would be satisfactory. The specs for my inverter is here. The computer itself has a 200W power supply, but sits there idle. The computer is a Dell Optiplex 210L. So lets say it utilizes... 100 watts. That would mean that it would be 0.10kWh. 0.10kWh X 12 hours would be 4,320,000 Joules.

6. Mar 30, 2013

milesyoung

Let's say you have a 10 kg lead-acid car battery (I'm guessing here since you didn't specify). If it's of decent quality and is in good condition then a specfic energy of around 30 Wh/kg is probably a good bet, so you get an energy capacity of 300 Wh.

Let's assume your inverter and computer power supply are 80% and 70% efficient in supplying AC and DC power, respectively, so you'd need 100 W/(0.8*0.7) ≈ 179 W from your battery, on average, which means you can run your computer for 300 Wh/179 W ≈ 1.7 h.

And again, this is a very crude estimate that's only supposed to give you a general idea of what you could expect. There's plenty of other things you need to take into account, like the discharge characteristics of your battery, for instance.

7. Mar 31, 2013

vk6kro

That battery is possibly capable of 85 amp-hours as this is the usual way of describing battery capacity.

So, suppose the inverter needs 150 watts to operate the computer and cover its own losses.

150 watts from a 14 volt battery would mean the current is 150 watts / 14 volts or 10.7 amps.

An 85 amp hour battery would last about 8 hours at a current of 10.7 amps. (85AH / 10.7A = 7.94 hours)

So, in this situation, you would need 3 batteries to last 24 hours. However, the actual current and battery capacity and inverter current would have to be measured to get a more accurate estimate.

Don't forget the monitor power, though. This is not powered by the computer so it would need additional power.

You could also consider using a laptop computer or replacing the hard drive in your computer with a solid state one.

Last edited: Mar 31, 2013
8. Mar 31, 2013

sophiecentaur

That would be very good advice. Someone has gone to a lot of trouble to design a laptop to use its battery energy efficiently and you could benefit from that. Also, you could do a lot better than using an inverter to feed the laptop PSU. A DC - DC converter could feed the laptop directly and avoid the losses associated with a mains inverter and PSU. They are available on line : this was the first google hit I came across.
If you have the money, then a solid state drive would be good, of course.

9. Apr 1, 2013

owen_a

Thanks for the help! The computer is only a server and is idle nearly all the time. It has 2 HDD's in there. Since I can barely afford anything, It'll me a while to get batteries. I'm setting up a small solar system in my room with at least 1-2 20W Solar panels on the roof.