Introduction: Portable Lighting System for Beach Volleyball
Given the widespread need for portable sports lighting, I was surprised at my inability to find any viable, cost-effective commercial products. Recently, the appearance of a wide array of household and automotive LED lighting products got me thinking a viable DIY solution is possible.
In this series of posts, I will describe in detail how to build a battery powered, portable sports lighting system from readily available components. While this system is designed specifically for beach volleyball, it can be adjusted and scaled for the technical requirements of other sports. In this first introductory post, I will lay out my overall scheme and discuss some of the component choices that I made. Subsequent articles will describe all of the modules in step by step build detail.
Every successful project requires a clearly defined set of design criteria. Here are the initial parameters I laid out:
- Portable (can be hand carried over a distance of a few blocks)
- Provide even and adequate court coverage
- Provide good quality of light (minimize hard shadows, blind spots, and excessive glare)
- Fully battery powered (no generator or need for AC power to deploy)
- Minimum run time of 3 hours on one battery charge (ideally 6+ hours)
- Easy/fast setup and teardown
I began investigating how bright a system I can create without violating any of the design criteria established above. The first step was finding a light source. The internet is full of cheap off-road automotive LED light fixtures that are weatherproof and operate on DC 12V power. These come in all manner of sizes, light patterns, and power ratings with the usual wild array of different branding for what appear to be the same lights. After staring at the dizzying array of options online for a few nights, I honed in on a few promising options and purchased some test units. The specific information I needed about light output, beam pattern, and power draw was completely unobtainable online, so I had to get them in my hands and test before settling down on a pair of Auxbeam 18W light bar fixture that uses 6 Cree LED chips.
I used a very seat of the pants test to gauge if the light output would be adequate. First, based on very subjective online reviews, there seemed to be a consensus that these 18W Cree light bars were "brighter than headlights". So, I pointed my car's headlights on the sand volleyball court and night and tried to imagine 5 more cars doing the same thing. Next, when I got the actual sample light fixtures in hand, I turned them on in my living room which is approximately the 1/4 the size of the court by floor area to gauge how well the space was lit. I didn't seem to have trouble doing normal tasks with 2x 18W lamps lighting the room, so generally, I felt the light output would be at least minimally functional.
The next major hurdle to overcome was how to get the lights high into the air and positioned optimally to get good coverage and quality of light for sports. I brain stormed cable and post systems, inflatable post systems, tripod systems, and finally concluded that simple telescoping painter's poles would be the solution. They are not particularly strong, but they don't need to be if the light fixtures they are supporting are lightweight. Initially, I would strap these to existing fence posts at the courts with nylon tie straps, and screw type beach umbrella anchors could be used on open sand.
I concluded that an 18ft. pole would be adequate height while collapsing down to 6ft. for transport which would fit in a normal car. Painter's poles are also fantastically light and all 6 can be easily hand carried in one trip. Some creative strapping may even allow them to be slung over a shoulder or transported on a bicycle.
With the posts and light fixtures decided, the next critical step was to determine my layout to evenly cover the court. The spot light fixtures that I chose were advertised as 30 degree beam spread, but in practice, they were more like 15-17 degree. Flood lights are also available for this fixture type advertised at 60 degree beam spread. But, when tested, they actually just threw light everywhere, and I feared I would lose too much efficiency with the flood lights given the large area I needed to cover and limited number of fixtures. With the spot lights, I could tightly focus all of my precious photons onto the court surface instead of bleeding them aimlessly into the night sky.
After studying commercial basketball and tennis court lighting schemes, I decided on a 6 pole layout with 2 light fixtures on each pole to provide even court coverage. For minimal glare directly in the eyes of the players, aiming the fixtures downward would be optimal.
But, according to my tests, at an 18ft. pole height, the beam spread of each light fixture would produce a small, concentrated circle which is not very even. So, I decided to keep the same light pole layout, but aim the fixtures across the court to the opposite side making the "spot" created by the beam spread larger and covering the court more evenly. Ideally, the beams should actually overlap to create the most even coverage, but we have to work with the light fixtures we have available and the pattern on this specific fixture is "loose" with a pretty gradual gradient at the edge of the beam and a significant amount of spill outside of the main beam.
The next main hurdle is the battery. The first thing that needed to be determined before evaluating battery options was the actual current draw of the light fixtures which I could not find on data sheets or anywhere online. Apparently, most of the folks installing these lights on off-road vehicles simply add as many as they want without considering the loads. Granted, the halogen fixtures these LED lights replace draw many times more power so the net load on a vehicle's electrical system is likely lowered even if a very large array of LED lights is installed, so I figure for most people, a tight calculation is unnecessary on a truck or ATV. But, we are trying to run as lean as possible with an absolute minimum specified operating time of 3 hours. So, the first thing I did when I go my test fixtures was measure the current draw at various relevant voltages.
12V - 2.137A (2 fixtures)
24V - 1.088A (2 fixtures)
This was fantastic news because I had initially guessed more than double the current draw for each pole. I initially thought lead acid deep cycle batteries would be the solution because by all the literature I see, they are the lowest cost. But, they are heavy and I would need to run hundreds of feet of cables to the poles. The cables would also need to be heavy gauge to overcome transmission losses on a low voltage system. For lead acid, I would have tried running 2 batteries each powering 3 poles. With the current draw lower than I originally anticipated, I wanted to check lighter solutions.
The next option was lithium batteries with each pole powered individually to keep cable runs as short as possible. I began looking at 22.2V or 6S lithium batteries. Lithium batteries are generally designed to cycle down to 20% charge which is better than the 50%-40% of lead acid batteries. I targeted a 10AH or 10,000mah 22.2V lithium ion battery because:
70% of 10AH is 7AH (assuming I run my batteries to 30% charge leaving a 10% buffer for safety)
7AH / 1.1A = 6.36 hours battery life
Further research revealed 2 viable types of lithium ion battery. The first is 18650 lithium cell popularly found in Tesla vehicles, E-bikes, laptop computers, power tools, and many other places. There is a lot of information available online about how to assemble 18650 battery packs. For my application, I would use Samsung INR-18650E (3500mah) cells. I would need:
3 cells per bank x 6 banks = 18 cells to make a 22.2V 10.5AH battery pack for each pole. At $3.70 each cell, for the batteries only, each pack would cost $66.60 and I would need to learn how to spot weld and construct the cells. Each pack would also require the addition of a battery management system to balance, and protect the pack (~$40)
The option that I chose for this build was lithium polymer packs commonly used in remote control cars, drones, planes, and helicopters. These have the advantage of having the most power density, but are more fragile and without any power management systems built-in, require special balanced chargers. Safe battery handling and storage are also important, and the internet if full of videos of mis-treated packs exploding into flames and burning down garages/houses.
I opted to use the RC lithium polymer battery packs because they were the lightest and did not require a lot of complex assembly. I may explore the 18650 cell option if I decide to assemble another system and compare them in actual use.
I ended up purchasing 12x 5200mah 6s lithium polymer (Lipo) packs. I will use 2 per light pole wired in parallel to give 10.4AH total.
Due to the potentially volatile nature of these battery packs, I purchased a charcoal smoker and am storing and charging the battery packs outside of the house in a covered back porch area so in the event one or more of my batteries explodes into flames, there will be no fire or smoke damage to my house!
With the battery packs determined, I need a way to efficiently and safely charge all 12 5200mah batteries. The RC Lipo packs are designed for high current output, and by RC vehicle standards, our application is very, very mild, so we can use low-cost options that are rated near the bottom end of the performance range for RC without stressing the batteries at all. But, by volume, 12x 5200mah batteries is a lot of batteries to charge and maintain and I will need a very strong charger to handle all of them. One of the best rated chargers for Lipo packs is the Revolectrix Powerlab 8x2. This charger has 2 channels and is capable of balance charging all 12 (6 per channel in parallel) of my Lipo packs safely in just over an hour. Progressive RC is a reputable US based shop with great customer support, so I decided to buy my charger from them.
Here, we can see the Powerlab charging 10 batteries simultaneously. The setup will easily charge all 12 batteries fully in well under an hour. In typical use, charge time is about 15 minutes.
With the majority of components on hand, I first executed a battery life test on one light fixture in my living room to confirm battery life. Running the batteries from ~83% to ~40%, I was able to get 3 hours of run time which is in line with the projections.
Next, I wanted to see how much light we are actually outputting, and determine if it is sufficient for playing actual games. For that, I would need to deploy poles on an actual court. For this test, I deployed 5 of the 6 final light poles because I am saving the last pole for step by step photo instructions on this blog.
El Nino has made weather conditions this winter very unpredictable, but on a clear night, I set out to test the partial system on a sand court.
After a bit of fiddling with the light brackets to aim and stabilize the lights, we were able to get the court reasonably covered.
I do not own accurate instruments to measure exact light levels, but I was shooting at ISO 2500 1/30sec exposure on my camera which by photography standards is pretty marginal. For 36W light poles on a fully portable system, the results are about as good as can be expected. We still cannot escape the laws of physics no matter high bright the amazon reviews say these lights are! I would guess the light levels are a good step lower than a recreational type municipal tennis court, but I was extremely happy with the quality of light I was getting and the even coverage.
We had no problems at all playing on the court and seeing the players and ball clearly. One concern that I had was if we would completely lose sight of the ball if it was hit very high because we do not have any direct lights pointed upwards and our lights are only 18 feet high as opposed a more standard 25 feet. As it turns out the sand surface is quite good at reflecting the light upwards and tracking the ball high above the court is not a big problem. The 5 light poles as tested created a good light distribution and glare is at a very comfortable level even when looking directly into the lights.
Another concern that I had was the color temperature of the LED lights specifically designed for efficiency as opposed to natural color rendering. The warm color reflecting off of the sand mitigated the typical blue cast of the LED lights acceptably, and the court rendered relatively warm and inviting to the eye. Also, compared to the horrible orange tint sodium vapor parking lot light in the background of this photo, I feel the overall color rendering quality of the light setup is not fantastic (ie. halogen lights) but ok considering the price of the fixtures used. It is not distracting or stark like many street lamps.
Overall, I feel the system performs quite well with 2 criticisms. One is we could use a brighter system in general, but we are about at the maximum weight these painters poles can support. But, because each individual light pole operates as an independent unit, we can easily add more poles to increase the overall light output of the system. The second problem is there are hot spots and dark spots on the court. Once we get all 6 posts in place, I think we will be able to have a better distribution of the light beams onto the court surface, and the problem should be all but fixed.
Even with these shortcomings, I feel the overall project is an overwhelming success and creates a very comfortable playing environment. While light output may be low for something like video production, my eyes did not feel strained at all playing on the court, and I could clearly see everything I needed to see. Certainly we have a solid "proof of concept" for a portable lighting solution. It should be noted that the total cost of the parts used in the system as described here is right around $2,000.00 USD. It all started with a $20 light fixture and quickly snowballed out of control, but I was happy I stayed inside of the original design parameters.
Part 2 of this series will detail some technical aspects of the battery charging system, and part 3 will discuss the light pole assembly, but for now, game on!