# A mobile power source for a laptop and a projector

My friend has asked me to do some marketing for his student targeted company. The hope is to create a good animation/flash video and project this (at night) inside the student campus onto the building. I saw a decent instructable here but this method involves a car/car battery. We need something more mobile as we will be situated inside the campus.

Could someone please suggest what power source I could use that would allow me to plug in the laptop and projector. Also could anyone suggest a good affordable projector?

• How long do you plan on running your projector? How much power does your projector take? What's the most weight/volume that you're willing to lug around?
– W5VO
Apr 5, 2011 at 19:39
• I want it to go for a couple of hours minimum. My laptop charger says on it "ac 19.5 v" .. inout 100v - 240v. I dont actually have a projector but I hopefully want something that is 2500 lumens, something similar to Acer X1261-3D
– brux
Apr 5, 2011 at 19:45
• also it must be possible to carry/drag on wheels
– brux
Apr 5, 2011 at 20:04

## 1 Answer

The cheapest way to carry a lot of power around without cords is probably going to be lead acid batteries. Let's figure out your power usage, and then go from there.

The basic system is going to look like this:

Battery -> DC-AC Inverter -> Projector
L> Laptop


We need to identify the load on the battery before we can estimate run time, so let's start with our loads. I was able to find a page that lists the operating power consumption of the projector as 224W. I'll estimate that you don't have a power-hungry laptop, and estimate power consumption at 40W. (You didn't include any current figures for the power supply, so I'm guessing.) This gives a load of 265W for the inverter.

I found an inverter that meets your continuous load requirements, and I calculate that it has a full-load efficiency of 78%. With a load of 265W, that results in an input power of 340W. This is effectively an average current of 29A at 12V.

The final step is to select the right battery. Battery capacity is measured in Amp-hours, and for every 30 Amp-hours you will get about 1 hour use. This sealed lead acid battery is 75 Ah, and it will last you for about 2.5 hours.

If you want to increase your run-time, you can:

• Find a more efficient / lower power projector
• Use a lower-power laptop
• Consider using a 12V laptop power supply
• Run your laptop off it's internal battery (thanks @jpc)
• Find a more efficient inverter (The one I linked to was the first I found)
• Buy a larger (Ah) battery
• Put multiple 12V batteries in parallel

All this should fit reasonably well on a hand cart of some kind. The battery will be heavy - the one I listed was 60 pounds. If this sounds like too much work/danger/weight, invest in a really long extension cord.

• While editing the title it occurred to me that we have to leave in a funny age when people need to drag 60 pound lead acid batteries to power their laptop for 2,5 hours. :P
– jpc
Apr 5, 2011 at 23:33
• You know what's funny? I forgot that laptops can operate while not plugged in.... shows you how I use my laptop :) At any rate, the laptop is only about 15% of the load. Just keep telling yourself it's for the projector.
– W5VO
Apr 6, 2011 at 2:34
• @W5V0 What can I say? Get a Mac(Book Pro)? ;]
– jpc
Apr 6, 2011 at 3:01
• @jpc It's almost 4 years old, and I always want the battery charged "just in case" I can't plug in. Although if you leave the screen off (you ARE plugging into a projector) your laptop could probably last for a very long time on its own battery.
– W5VO
Apr 6, 2011 at 4:03
• Thank you for this great answer it was very useful indeed
– brux
Apr 6, 2011 at 17:01