DIY Portable Solar Generator

18ah Portable Solar Generator " Watt Box"

Final Product

-18ah 12v solar generator that includes a solar controller, 2X 5.5mm ac ports for LED light output/ solar panel input. Cigarette lighter port for charging electronics. A 20watt solar panel will recharge this unit in about 10-14 hrs

I chose to go with the ammo can as the enclosure due to its durability, water tight seal, and its cheap price. All the components fit perfectly inside with little room to spare. Weighs about 13lbs total.

Running two 2 9aH SLA batteries in parallel puts out 18ah worth of power. On paper calculating the run time to power something is nice and all but nothing works better than running actual tests. I was able to get about 10hrs of light time powering a standard 12v 150 RGB LED light rope (16ft long) on full brightness. I was also able to get 5-7 complete phone charges on my S5 (2,800 mAh) on a separate test.

With a 20 watt solar panel, the entire unit takes about 10-14 hrs to charge, and that's in Chicago too so I'm sure it would take less the more south you are. The solar controller shuts off at about 40% to prevent your batteries from completely draining, this helps with extending the battery life. You want to make sure that your batteries are not sitting around discharged for more than a few days at a time.

Parts list

Google Docs spreadsheet with links and prices here --> https://docs.google.com/spreadsheets/d/1UsmlZeanijspCLUKki-D9uh1d5Bytyb3oJKT2-ex3uw/edit?usp=sharing

a. .30 Cal. Ammo Can (used)
b. Solar Charge Controller
c. 4X Plastic washers for 6-32 screws
d. 2X 5.5 MM AC PANEL MOUNT PLUG
e. 9X Foam pads 3/8" thk.
f. 12V Power Socket Cigarette Lighter Plug
g. Blue Led Dot Light 12V SWITCH
h. ~4.5 in. x ~2.75" in. Polycarbonate Sheet
i. 16 ga. Red & Black wire, ~18" ea.
j. HEX STANDOFF 1/4" Hex Size, 1-1/2" Length, 6-32 Thread Size
k. 8X 6-32 screws, .25"-.5" long
l.4X FEMALE QUICK DISCONNECT, 0.11IN
m. 3X FEMALE QUICK DISCONNECT, 0.188IN
n. *6X FEMALE QUICK DISCONNECT, 0.25IN
o. 2x 5.5mm ac plugs (to power LED lights)

~Not Shown
-2X 9aH SLA batteries
-20 watt 12v solar panel

Tools needed

a. Glass cutter
b. 1/8" Drill bit
c. Step drill bit
d. Wire stripper
e. 9X Foam pads 3/8" thk. (already mentioned)
f. Flat head/ Phillips
g. straight edge/ ruler

~Not Shown
-Drill

The solar charger is too wide to fit in the box nicely so we'll be taking off the case.

2 screws on the case, 4 screws on the circuit board need unscrewing. We're going to mount the circuit board to the side of the ammo can with the 4 clearance holes on the board.

Trace the hole pattern of the board onto the Lexan sheet. Trace the side as well .

You want to score about half the thickness of the Lexan before you snap it.

Karate chop that hanging piece off

Drill the 4 clearance holes with the 1/8" drill bit

Taking of the lid makes life easier. Just slide it to the right side to get it off.

Drill pilot holes before you use the step drill

Step-by-step

Hole placement for the cigarette plug

Hole placement for the on/off switch (on opposite side of the box)

Hole placement for the 2X 5.5mm AC plugs

Trace hole pattern of circuit board about .25" from the bottom on center. Drill using 1/8" drill bit

The big cable is the positive battery cable & the small cable is for the On/Off switch to solar controller. You'll be sharing 2 cables with 1 quick connect.

Negative battery cable

cut to ~3" long

Crimp the quick connect sockets to the end of the stripped wires

You want to check the date sheet of the 5.5mm ac ports to locate to correct terminals. There are many of these on the market.

Try to purchase the 5.5mm AC plugs with .11" terminals. Connect the wires using the 4 .11" female quick connect sockets.

I did't get the right ones so I just twisted the wire in place then used hot glue to seal them.

Now to mount the solar controller

Place the 4X 6-32 screws in from this side, on the other side slip in the plastic washers .

Wiring Schematic

After the plastic washer, slide in the solar controller thorough the screws. Use the hex standoff at the other end as a nut and fasten the board in place.

It's easiest to start wiring the two loads wires ( Cigarette plug & 5.5mm AC plug). Those will share the same port on the solar charger.

The other AC port for the solar panel will be mounted in the open hole shown above, they will go into the terminals furthest right. I hope you didn't throw out the plastic case for the solar controller, this is a helpful reference for getting the terminals right.

After wiring the solar input, the last terminals left should be for the battery cables (2 in the middle)

The last ast things to mount is the cigarette plug and finally the Lexan cover. The Lexan not only helps with covering the solar charger for safety reasons but it also spaces out the batteries so they don't damage the wiring.

The foam pads I used were scrap from work. They don't have to be circular.

Stick the pads on the top of both batteries

Line the inside of the box with the pads so that the bottom and sides of the batteries are insulated. This makes the batteries fit nice and snug.

Wire the first battery closest to the switch to the appropriate terminals.

Wire the last battery to the end of both power cables we made earlier. Both batteries are connected only by their matching terminals (pos+ to pos+, neg- to neg-)

Always a sign of relief when that light comes on

Testing all the ports

Wire the solar panel so that the end of the cable is a male 5.5mm AC plug (I don't recommend this way for future builds, I rather use more expensive MC4 cables along with a SAE port)

Notes of operation

You want to make sure that the generator is turned off whenever you're not using it. The solar controller has led lights that are always on as well as the on/off switch. If you keep this on the battery could drain to zero which will damage the battery.

Also make sure to turn off the unit once the sun is setting and disconnect the solar panel. The panel seems to discharge the batteries a little.

Changes I'd make for future builds:
-I would include a built in fuse in the battery cable to the switch
-Solar port would be a SAE port instead of a 5.5mm AC port
-Add a ground cable
-Add a battery status indicator
-Add another input for the option of charging the unit with a wall charger

Thanks for looking.

I have already purchased most of the components in bulk to get a cheaper overall price. If you want buy one of these already built and assembled please check out my Etsy store. I have the same unit above for sale for $125 plus shipping.

https://www.etsy.com/listing/386085582/watt-box-20w-portable-solar-generator?ref=listings_manager_grid