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.
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. The security light 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!
