Step 1: Power Inverter Mods

Picture of Power Inverter Mods


First, disassemble the DC/AC power inverter. There are four screws on each end cap. Note how all the wiring is connected. Cut the wires to the AC receptacles and remove them from the enclosure. There are tabs that hold them in place. Desolder the leads from the receptacle.

Remove the fan and extend the leads about 6 inches. You can add an optional header to the board and a pin connector to make reassembly easier. Save the four mounting screws and fan guard since you’ll be using them.

Desolder the USB connector from the subassembly board which holds the power switch. Extend it by soldering a USB cable connector. These USB connectors can be found on the back of old PCs. They occupy a card slot. These style connectors are great because they have integrated mounting tabs. Mounting a raw USB connector to a panel is difficult.

Step 2: Prep the Ammo Box

Picture of Prep the Ammo Box


Mount the flood lamp to the top lid near the hinge. You’ll need to cut off some ribbing on the back side of the lid before drilling a hole for the lamp bracket.

Create a template from the holes for the AC receptacles on the end cap of the power inverter. Transfer the template to the lower front of the ammo box. Using a Dremel and utility knife, cut out the AC receptacle holes. Using a hole saw, drill a hole for the fan and the 12V car accessory jack. Drill the remaining holes for the DC power jack, switch, USB connector and vent openings at the top. Note, one of the vent holes is used to route the lamp cable.

Step 3: Fabricate Internal Frame

Picture of Fabricate Internal Frame


One of the main design concerns for the project was airflow. The power inverter has a fan so the box needed to be designed to allow for adequate airflow. The internal frame was designed to have two levels. The lower portion contains the fan and power inverter. The top contains the relay board, battery charger module and power button sub-board for the inverter. The air gets sucked in from the front. Then it does a 180 degree turn to the upper level and then out the top vent holes. See the side view diagram for details.

First, fabricate the lower base plate. It should be sized so that it fits inside the bottom of the ammo box. The material used is scrap pegboard. A jigsaw is used to cut it out. Cut out some smaller pieces of pegboard and use them to block in the power inverter board. Position, then glue these smaller pieces to the larger piece. Allow room for the battery. See photos for more details.

Next, fabricate the four legs. The legs are used to hold the top plate. The legs are made from strips of aluminum sheet. Using metal snips, cut out two long strips. These are roughly 3/4 in. wide by 10 in. long. Bend these in a “U” shape and epoxy them to the lower base plate. Wait a day for the epoxy to dry. When dry, bend the ends of the four legs inward. Drill holes in each of these ends. Then thread bolts into these holes. The four bolts should be pointing upwards. Epoxy these bolts in place from the underside. See the side view diagram.

The 12V car accessory (cigarette lighter) jack comes with a “L” shaped metal bracket. Use this metal bracket as an upper support for the top plate. Just drill the end of the metal bracket and epoxy a bolt to it, similar to the support legs fabrication. See the photo for details. Solder a crimp lug to the bracket. This provides the negative power to the 12V car accessory jack. The top plate should sit on top of this bracket.

The top plate is made from 1/8 inch acrylic sheet. It was heated and bent to form a “Z” shape. First create a template in cardboard. The top level of the “Z” should be above the fan but below the DC power jack, switch, USB connector and vent holes. See the photos for details.

Transfer that template to the acrylic sheet and cut it out with a jigsaw. Using a metal brake and a heat gun, bend the acrylic to the desired “Z” shape. Next drill 5 holes that align with the bolts that were epoxied to the legs.

Fabricate a small mounting board for the inverter sub-board that holds the power switch. Use sheet ABS and screw the sub-board into it. Drill two holes in the ABS that align with the epoxied bolts on two of the legs.

Lastly, position the battery on the lower base plate. Create a slot in the plate so that the nylon web strap can be used to strap the battery to the lower base plate.

Step 4: Make the Relay Board

Picture of Make the Relay Board

The relay board is used to turn on the lamp if the power mains goes down. This can be used as an emergency flood lamp. The way this works is that it monitors the power mains. When the power goes down the relay board turns on the lamp.

The battery charger has a small wall wart. The relay board monitors the output of this wall wart. A simple circuit keeps the relay coil energized using the output of the wall wart. When the power mains goes down, the relay coil de-energizes which flips the lamp on.

Unfortunately, the output of the charger wall wart is AC so it must first be converted to DC. The relay coil works only with DC, hence the need for the relay board.

The construction of the relay board is simple. It consists of a diode bridge and 7812 voltage regulator. Install the components per the wiring schematic then solder everything.

Next, modify the battery charger. Cut the wires from the wall wart and install a DC power jack and plug. (The photo shows the float charger module with the cover off. Prying the cover off isn’t necessary.)

Lastly, position the battery charger module and relay circuit on the acrylic top plate. Drill and tap some mounting holes.

Step 5: Final Assembly

Picture of Final Assembly


The final assembly is the best step. It’s a culmination of all your hard work.

Paint the parts, as needed.

Mount all the front components: AC receptacles, fan, fan guard, 12V power jack, DC power jack and switch. Then position the power inverter board and mount the USB connector. Using crimp connectors wire up the AC receptacles and battery terminal leads. Thread the battery strap through the plate and bolt the plate to the ammo box.

Using more crimp connectors wire the fuse holder to the 12V accessory jack. Install the top plate and mount the inverter power switch sub-board, relay board and battery charger module. Following the wire diagram, wire up and solder the remaining circuit.

Test the circuit by flipping the lamp switch on. The lamp should light up. Then plug in the battery charger wall wart. The lamp should turn off. You should hear the relay toggle. Test the AC power by plugging in a desk lamp or similar appliance. Test the 12V car accessory by using a multimeter or inexpensive cigarette lighter type voltmeter.

Congratulations! You finished! Enjoy your new portable sun!