Determining power needs for "guerilla drive-in" theater

My family is planning to spend a week camping together for our family reunion in August this year, and for at least one of the nights I'd like to set up an impromptu drive-in movie theater, projecting a movie onto a sheet or something similar hanging on the side of my trailer. The challenge is that we will be in an area that does not have RV hook-ups (so no electric grid) and it doesn't get dark enough for a projector outside until well after 9 PM so using a generator is only possible for a short time before the 10 PM "quiet time" kicks in, and the noise of a generator would be pretty distracting while watching a movie anyway, so I need to figure out if I can make it work just using the available power from my trailer battery and I'm not sure how to calculate things properly.

So, here are the relevant specs:

96 Ah* capacity Interstate Group 27 deep-cycle 12 Volt RV battery
Optoma ML1000P projector
300 Watt* DC/AC power inverter in the trailer
A laptop will provide the video source and will send the audio directly to a pair of self-powered speakers. The laptop has a battery that can easily handle over four hours of video playback so it does not need to be plugged in while the movie is playing. The speakers last about 10 hours on a charge so they also don't need to be plugged in.

* I'm pretty sure these are the right numbers but I'll have to pull the trailer out of storage and open it up to be sure.

The label on the projector lists the power input as 100-240V / 1.3 A and the manual shows a Max Power of 145 Watts, but I can't find anything that says what the actual normal power draw is. I could measure it if I had a Kill-A-Watt, but I don't and I'd rather not buy one since I have _almost_ no need for one, so I'm wondering if there is a way to get a ballpark estimate with that information.

I will not be using the two internal 3 Watt speakers in the projector. They will be muted and I'll use a pair of nice Bluetooth self-powered speakers instead, so the internal speaker power usage can be discounted from the total. If the necessary power for a 2 hour movie will be just slightly more than the capacity of the battery, I can also connect my tow vehicle to the battery with jumper cables battery to share its power, but I'd rather not do that if I don't need to since the car battery isn't designed for continuous deep power drains like the RV battery. Any power that is used can be recharge via generator/solar the next day.

I believe that it's best to not drain an RV battery below 50% and they should never go below 20%. I'm willing to let it go a bit below 50% for a one time thing if it won't cause significant/permanent damage, but I'd like to leave a little bit of juice for the fans in the trailer if it's particularly warm outside, so let's say there's about 50 Ah available, plus maybe another 10-15 Ah? that can be added from the tow vehicle during the show if needed. Am I asking too much of the battery to run the projector for 1.5-2 hours or is this doable? If it's not possible to make an educated guess, I can pull the trailer out of storage and hook the projector up to see how long it takes to drain the battery to 50%, but I'd like to try to get an estimated run time first in case it's not possible at all.

Any suggestions how to determine the power that I need, or otherwise measure things to see if it will work? The trailer is stored at my parents' house right now so I'd have to drive over, open it up, check things out, and spend the full rest of the day chatting with my Mom (it's a requirement for anyone that goes to visit )..

 

If that's the case, then I should be able to easily get it done within the limits of the battery. I suppose I should probably go ahead and pull the PUP out and let the projector run off the battery for a couple of hours to verify it doesn't drop the charge level too much before we actually go on the camping trip, but at least it looks like it should work. Thanks again!

 

The drive in movie was a success. The nearly two dozen cousins and my siblings and their spouses all had a good time watching a movie while sitting in the field/campground almost in the middle of nowhere. We ended up using a big white tarp for the screen and while it wasn't movie theater quality, it was lots of fun. Running the projector for just about 2 hours drained my battery from pretty much full (12.75 volts) down to about 60% (12.22 volts) so it wouldn't be able to handle two movies in a row without going well below 50% charge, but it worked great for the one movie that I really wanted to do.

I did find out that while my boring 45 watt solar panel array (Harbor Freight special) has been adequate to recharge the battery from normal overnight power usage, it wasn't able to get the battery back up to full power the day after the movie. I was also recharging the laptop through the inverter at the same time and I'm not sure how much that took away from the charging process on the big trailer battery so it might have been enough if I didn't need to charge the laptop. It's not really a big deal since we won't be doing movies very often, but it was the first time I had drained the battery enough to notice, and now that I know, I "have to" put a better panel on my wish list for the future..

Thanks again for the help with the math and the planning!

 

More batteries and a generator would be great, but just not in the budget at all right now or in the near future. For now I'm just happy that the battery and inverter performed so well running the projector for a few hours.

I definitely love the cargo deck in the front of our trailers. It makes packing so much easier and is one of the reasons why I picked the RT line over some other trailers I looked at!

I like the lounge/dinette area in yours. It adds some much needed seating. Ours has the dinette in a pull-out on the street side of the trailer and that adds a little more floor space, but not much seating. I guess they both have advantages and disadvantages.

 

I wouldn't use a big "theater" projector for this either. The one I took is designed to be a business presentation projector, so it's relatively small, not particularly expensive, low power demands, but still adequate for a bit of fun on the camping trip. Sadly, it does not do a good job of reading/playing movies directly from USB so I had my laptop do all of the video processing and just sent the signal out via HDMI. It worked nicely.

Pico projectors can be fun, too. But I wanted to project a pretty big image for extra silliness for this trip since there was such a large group (ended up about 20 feet across) and most Pico projectors I've seen don't put out enough light to do that effectively. The few I have tried got pretty dim even at night with no ambient light when projecting an image larger than a few feet across.