Determining power needs for "guerilla drive-in" theater

Discussion in 'Power - Site Power/Batteries/Generators/Solar' started by BirdsNest, Jul 3, 2017.

  1. BirdsNest

    BirdsNest Active Member

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    Jun 12, 2017
    Utah
    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 ;))..
     
  2. SteveP

    SteveP Active Member

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    May 21, 2015
    Based on your data, 145 watts + 20% for the inverter for 2 hours = (145 watts/12 volts)*1.20*2 hours = 29 amps.
     
    BirdsNest likes this.
  3. BirdsNest

    BirdsNest Active Member

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    Jun 12, 2017
    Utah
    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!
     
  4. BirdsNest

    BirdsNest Active Member

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    Jun 12, 2017
    Utah
    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!
     
  5. roybraddy

    roybraddy Well-Known Member

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    Mar 23, 2016
    King George, Virginia
    I have much the same appliances you have with my 2008 Starcraft 14RT trailer. I added a 13,500 BTU Air conditioner on the roof from the dealer in 2008 and did a few camping trips. I right away boiled out my single 12V 85AH Interstate battery and decided I better replace my single mode 13.6VDC ELIXIR 30A Converter/charger setup with a PD9260C 60A Converter/charger and install a more modern Power Distribution center to replace the 2 full size 120VAC Citcuit Breaker slots and three 12VDC Fuse zone locations. I also also beefed up the battery wiring to 4AWG and changed my ceiling lights to LEDs... I wanted to go with four Group 24 85AH Ineterstate batteries but I could not bring back my over charged initial 85A AH battery.12V battery. I ended up installing three new 85AH Interstate 12V Batteries across my trailer tongue area.

    My tongue setup is two Prone tanks in front behind the trailer jack with the three 12V Interstate batteris between the propane tanks and the trailer 5x8 front deck... been using this setup since late 2008... I was going to mount 4ea 85AH 12V Interstates here which would have made me extend the mounting agnle out 12-inches on each side of the tongue. As it turned out three of the GP24 Interstate fit just perfect with the OEM welded in angle rails.

    [​IMG]

    This is my 14RT Floorplan which is probably very similar to your 13RT model
    [​IMG]

    After adding the multiple batteries my floorplan now looks like this but only has three GP24 Batteries across the tongue area.

    [​IMG]
    Roy's image

    With the three GP24 batteries setup we can run just about everything we could do at an electric site when camping OFF-GRID with the exception of NO Air Conditioning or High wattage Microwave use... We actually camp off grid more than we do at regular campgrounds...

    This is my battery bank setup diagram except I am using a 600WAT PSW Power Inverter...
    [​IMG]
    Roy's image

    With this setup we can draw around 20-25 AMPS drain from the batteries from 6PM to around 11PM each night and only drop my batteries to their 50% charge state (around 12.0VDC) after going to bed and running all of the required parasitic drains .. Then at 8AM the next morning we will start up the 2KW Generator when allowed adn power up the trailer 120VAC shore power cable and charge the batteries back up to around their 90% charge state in about three hours of generator run time each morning. Then we good to go again for the next day/night run off the batteries.

    Been doing this since 2009 and just last season my three 12V batteries started to lose performance and not hold my re-charge very long.

    I am now in the battery box replacement mode and have my TORKLIFT 59-inch metal battery box all made up for two groups of four 6VDC GP 24 Trojan T105's batteries which will give me a good 440AH's battery capacity. This will fit very nice across the tongue area where my other batteries were installed. Perfect fit...

    My success is monitoring my batteries like a hawk when camping off-grid and when they hit the 12.0 VDC charge state I shut them down and then begin a re-charge using my 2KW generator when allowed. Hopefully this season I will be able to afford my T105's and start camping again off-grid. I am also a Ham radio guy and all of that requires more battery capacity as well...

    Your RT13 also has the front deck and like mine along with my truck bed we can bring along some serious camping supplies with us.

    [​IMG]
    Roy's image

    Wouldn't have it any other way haha...

    Just passing all of this along to give some additional ideas perhaps...
    Glad to run across another Starcraft RT series owner...

    Roy Ken
    [​IMG]
     
  6. BirdsNest

    BirdsNest Active Member

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    Jun 12, 2017
    Utah
    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.
     
  7. inthedirt

    inthedirt Active Member

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    Aug 28, 2012
    SW Montana
    I've been attending the same family reunion campout for the last 4yrs and have also implemented a "movie night," or two. Personally, I wouldn't ever take a laptop and full size projector on a trip like this simply because of the liability. Something always goes wrong and things get ruined. I've found that the pocket or Pico projectors work pretty good for this scenario. I've used a couple different kinds and ended up returning them right after our trip because they didn't quite perform how I expected them too. Perhaps my expectations were too high? My current setup is also the simplest to use/store. I have a Droid Moto-Z phone and the Moto-mods that attach to it are phenomenal. One of the attachments is a projector with its own built-in battery. When the two are connected, the projector will draw from the phone's battery once the projector battery is used up and they both charge from one connection to the phone. I carry a pocket lithium 5000ma battery and cable to attach to the phone. This will get us through 2-3 movies before anything needs recharging again. If I need more juice than that, I also carry a jumper box in the truck for emergency jumpstarts. It has a 12v aux port that I can plug the phone into. All of this is portable, and because I use the phone/projector for work (healthcare), its all a right-off on my taxes! If you go with a pocket/Pico projector, they typically have SD cards or built-in memory to transfer movies from your computer. Just be sure to compare their outputs. You'll want to get one that has the highest rating (lumens) that your wallet can afford. This will give you a better picture in low light conditions. My Moto-projector isn't that great unless its completely dark, but I can bluetooth to any of the speakers out on the market or to my Pup's stereo if viewing onto a curtain on the inside. Hope this helps!
     
  8. BirdsNest

    BirdsNest Active Member

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    Jun 12, 2017
    Utah
    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.
     
  9. inthedirt

    inthedirt Active Member

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    Aug 28, 2012
    SW Montana
    Gotcha. Seems we're on the same page. The biggest screen I've done on my phone was 13ft, so still plenty big for us. I just hate carrying around something that large to use as a screen. I took my awning off the side of the Pup because it interfered with the roof rack I fab up, but the awning "rail" is still attached. I might remove it completely and reattach on the road side, just below the rack mounts. I don't ever use the awning, but I could likely use the rail to keep a screen rolled up and attached to the side and ready for deployment. Hmm......looks like I have more fab work to do!
     

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