Santa Clarita and Northern Los Angeles County Area
Butterfly and Moth Site
Battery-powered 175w Mercury Vapor Collecting Light
This is not a new idea, but with a little shopping and some handy-work, it can be very affordable and relatively portable. The system described below can be built for around $200, and probably much less if you already have some of the parts and/or are willing to build instead of buy! Of course you can use other brands and higher-end suppliers. However...
Please note that this particular combination (brand and model) of MV light and inverter worked very well where many others have failed, and are probably the most critical parts in this setup. More detail is provided below.
Most of the components are available either online or at local giganto-stores such as Home Depot or Costco. Part numbers and typical prices are included below.
Here are pictures of the rig as originally built and tested successfully. It's compact, battery powered, and simple to set up. The only component not shown in the picture below is the battery charger. Run time is about 3 hours on a full, fresh charge.
Below you'll find the equipment list and construction/use notes:
Large 12v car battery: Costco, about $35 (No online pic or link available)
I used a Sears DieHard that I happened to have. I wasn't sure of its condition, but after testing yielded 3 hours of run time, I figure it was in pretty good shape. A deep cycle marine/RV battery is the best choice for maximum usable amp hours. Beware that leaving any lead-acid battery in a discharged state is bad for it. The output and lifespan will be shortened, so recharge it as soon as possible after use. See the charger section below for more charging details.
Battery Charger: Harbor Freight Tools, about $25
Just about any generic automotive battery charger will do. It should have a switchable 2 amp and up to 10 amp (low/high) setting. The charger shown has a high setting of 6 amps. It will take a little longer to charge, but otherwise is fine. A built-in overcharge protection feature is also a good idea.
As soon as possible after use, place your battery on the charger on HIGH overnight. A discharged battery will be very thirsty and will happily eat 6 to 10 amps for 10-12 hours. Note that the battery and charger may get very warm. Be sure to provide good ventilation as charging lead-acid batteries produces heat, hydrogen gas (which is explosive), and sometimes sulfuric acid vapors (very corrosive to nearby items). I have noticed a slight pungant smell of acid (similar to chlorine) in my garage the morning after a full night of charging. After 10 hours or so on HIGH, set the charger to 2 amps and leave it for a few days, then disconnect and store it. Before going out again, put the battery back on the charger at 2 amps for 24 hours to ensure a fresh charge for maximum run time.
It may be an "old wive's tale", but I have heard that storing a lead acid battery on a concrete floor will accellerate its self-discharge rate. Whether or not it's true, store your battery on a slab of wood or similar, and place it on the charger for 24 hours once per month at 2 amps. Be sure and check the water level regularly, as charging and discharging evaporates the water.
Mercury Vapor Security Light (Item #325585): Home Depot, about $30
This is Home Depot's least expensive mercury vapor light. Just click the link above and then type the item # in the search field in the upper right to locate the product. Last time I checked, the product picture was wrong and by now there by something completely different. The security light I used is a 175 watt model, made by "Regent" and is a cast aluminum housing with a transparent plastic lens/shroud. A number of modifications need to be made to the housing and wiring in order to get the best results.
The fixture is designed to be hardwired directly to an electrical box - no plug is provided. Using wire nuts, I connected a 3-foot electrical cord and plug that I scavenged from a junk electrical device. The system operates in two modes:
1. Bulb-up with the lens/shroud removed for clear weather and better light exposure.
2. Bulb-down with lens/shroud installed for rainy weather. This limits light exposure, but protects the bulb - if raindrops were to land on a hot bulb, the temperature shock could cause the bulb to explode!
The light comes with a mounting "arm" which extends about 10" from the side of the housing, for mounting to an electrical box. For tripod- mounted use, I opted to remove the arm with an angle grinder, and fill the hole with a piece of sheet steel. The first two pictures below show where the amputated arm used to be, and the filler piece.
The metal and plastic lens/shroud (picture 3) can easily be installed/removed with two screws. When removed, the inside of the housing is exposed, so I cut and drilled a round piece of plexiglass (pics 4-7) to keep bugs out of the ballast.
To secure it to a tripod or other stand, I drilled a hole in the side of the housing and tack-brazed a nut on the inside that mates with a standard camera tripod mounting screw. (picture 8)
On the top of the light fixture, there is a removable light sensor module, that turns the light on at dusk and off at dawn. (first two pics below) It consists of a phototransistor and bi-metalic strip which acts as a switch. You can probably use the light as-is, or paint entire sensor black to prevent the light from shutting down while in use. I opened up the sensor and adjusted the setscrew all the way out, (pic 3) so that the switch so that it can't actuate.
400w/800w surge inverter: Harbor Freight Tools, about $40 ($30 or less when on sale)
A Chicago Electric brand 400w/800w surge unit was used for this project.
I chose an inverter with roughly 2x the wattage needed to run the load. The MV light will draw about double it's rated current at start up, so a big surge capability was needed too. This inverter easily handled start up and the continuous load without complaining or even getting warm. At just about 3 hours of run time during testing, the battery voltage had dropped to just above 11 volts, and a warning alarm in the inverter sounded. At that point I shut the light down and placed the battery on the charger.
Hooking up the inverter is a snap. First, connect it to the battery using the short heavy gage cables/clamps provided. A good solid connection is important as it will draw about 25 amps when the MV light starts-up. Then Plug the MV light into the 110VAC outlet on the inverter and flip the power switch on.
Note that extending the battery cables, or using smaller gage wire could starve the inverter and prevent proper operation. If you need longer distance between the battery and MV light, use a 110VAC extension cord between the inverter and the MV light instead of extending wiring between the inverter and the battery.
Tripod or other holder: source and type varies, about $30
The tripod shown came from a local swap meet, used, for $10. It's strong and highly adjustable. Many mounting variations are possible. Be careful to choose a strong and stable stand. The light assembly weighs several pounds - a top-heavy stand could fall over, causing it's destruction and injury to anyone nearby.
Assorted hardware, wiring, etc: about $20
You shouldn't need much; A reasonably heavy, short (3') AC electrical cord, a few wire nuts, electrical tape, small piece of thin plastic, a nut that matches your tripod mount... All very scavenge-able stuff!
Because the bulb is so fragile, a protective transportation container is a good idea. This one is made from a heavy cardboard box, with bubble- pack wrapping. Always let the bulb cool before putting it away. Keep the glass as clean as possible to transmit maximum light and reduce inward heat reflection. A dirty bulb will get much hotter and not last as long as a clean one.
This system is fairly compact and easy to transport, except for the battery. If you plan to use it in a remote location that you can't easily drive to, a hand-truck or "dolly" really helps. This one comes from Harbor Freight Tools and typically costs about $20. Big fluffy pnumatic tires help prevent excessive vibration of your equipment. Bungee cords can be used to secure the equipment. The battery should be kept as upright as possible. The triangular wooden block is used to keep the battery upright when the dolly is pulled along at a 45ø angle to the ground.
If you can drive to your collecting location and want to use your car's battery instead of a stand-alone battery, you can connect the inverter directly to your car battery. Don't use your car's cigarette lighter plug, even though one is provided with the inverter. Chances are good that the high current required to start the MV light will be too much and could blow a fuse or overheat the car's wiring.
You should start and run your car's engine as needed to prevent the battery from becoming so discharged that it can't be used to start the car! You may need to shut down the MV light when starting the car, but can turn it back on as soon as the engine is running. When already hot from use, the MV light should come right back up to full brightness quickly.
Have success or failure with this or a similar project? let me know!
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