36 Volt - 900 Lumen LED Stadium Lights

The end of daylight savings and no lights meant that 5:30 pm soccer practice would be totally dark. With field space severely limited this meant the end of practices.  Next year we will be ready with portable battery powered field lighting, thanks to low cost, high power LEDs and lightweight long lasting lithium 36 volt battery packs from Dewalt.

I built two stadium lights. Placed on opposite sides of the field they do a nice job of lighting a decent size practice area for 10-12 kids. For a larger field or different sport, you may need several more. Each light draws ~.750 Amps, the Dewalt pack is good for 2.3 Amphours or not quite 3 hours. Still more than long enough for practice. 

Needed  36 Volt Dewalt Lithium battery pack
These things are great, lightweight, fast charging,  and very convenient after you have followed the directions to add standard power out wires. I will not detail how to disassemble the battery as this is readily available on the internet in several places.
http://www.slkelectronics.com/DeWalt/packs.htm
http://www.youtube.com/watch?v=qQJUEeKo7KQ
9 STAR LEDs (3 watts ~100 lumen each now available direct from China for around $2 per LED, ebay and other sources)
Most  of these high power, high efficiency LEDs operate from 3.5 to 4.0 Volts.  To save money we are not going to use the recommended constant current driver, but wire directly in series. (36 V / 9 LEDs) = 4.0 volts per LED.
CPU style heat sink
1 ohm, 10 watt resister (to add some safety margin)
18 inch long piece of aluminum angle (1/16" by 1 inch)
JB Weld Epoxy
1 inch hose clamp
10' x 1/2 pole (PVC pipe)
Screws, wire, solder

Step 1 Solder Leads to the Star LEDs

STAR LEDs are very nice to solder. They have wide solder pads, clearly marked + and -.  Start with the plus side and solder one lead to one + pad.

Comments

[rimar2000]

Interesting.

Besides portability, does this device advantages over a low energy lamp connected to the mains?

[pobriant]

If you have an electrical plug easily available, I would recommend keeping it simple and plugging in with standard lighting. The soccer field is 1/4 mile from my house and my extension cords are not that long.  But if you needed a combination of high efficiency and robustness (where the light was going to be knocked around a bit) a plug in LED solution might be the best. High power LEDs are much more efficient than standard incandescent or halogen bulbs.  And much more robust then florescent bulbs.

[rimar2000]

Thanks for the answer.

I forgot to ask something that interests me more: are LEDs more expensive than equivalent  "ordinary" lamps?

[pobriant]

You just asked the multi-billion dollar question that is driving today's lighting industry. The answer may be  "it depends on when you ask". 

The one thing most agree on is that  the standard cheap incandescents have lost. Go to Home Depot and on sale you can get a 60 watt incandescent bulb (claimed 15 lumen/watt = 900 lumens) for around $1. Plug it in for 24 hours a day and you will spend ~$52 of electricity.  (60 * 365 *24 / 1000 watts/kilowatt) * 10 cents per kilowatt hour, about US avg. (total $53)

The el cheapo $2 LEDS I used are about twice as efficient, 33 lumens/watt. So 9*$2 = $18 but I would only use $24 of electricity per year. (total $42)

Gross simplification and does not include fixtures, AC/DC converter, converter  efficiency,  replacement bulbs, etc. But you get the idea. Invest now, save later.

Today florescent  (up to 100 lumens/watt) easily beats both for most applications but are not robust for banging around as portable lights or smashed by an errant soccer ball.  Cree/Seol/Nichia/Philips all claim to have next generation LEDS with efficiencies from 130 to 150 lumen/watt.  And where LEDs may make sense today is if you are off-grid and already running DC power.

[rimar2000]

Thanks for that excellent summary of the situation. In my case, I will follow the mainstream, replacing filament lamps by low power as they get knocked out.