Emergency rescue workers from International Rescue Group asked the altE Store for a way to charge their phones and tablets while helping the hurricane survivors in Haiti. We built them a couple of portable solar powered systems that are small enough to allow them to carry it around where needed, while big enough to recharge many phones and provide some lighting as needed, even when the sun is down. Each system costs about $280. If they want to power AC items, they can add an inverter to convert the DC from the battery to AC to plug into for about $100, depending on the size and model.
18AWG wire - 2 wires $0.59/foot (we used 20' to allow the panel to be outside in the sun while keeping the rest of the system inside)
Strain Reliefs $2.21 each (2 used)
9 QT Cooler $10
DC Connectors $1 each (2 used)
Wire connectors $0.07 each
DC Lights $15 for 8 lights (used 4)
Optional Samlex 150W 12V inverter - $117
Step 1: Figure Out How Much Power You Need
This step is so often ignored, yet is one of the most important steps. If you have specific items in mind that you are trying to power, you need to know how much solar and battery you need to power it. You can go to an online Loads List Calculator to see how much power you need, and then an Off-grid Calculator to see how much solar and battery you need for it.
For this system, I figured on charging 3 cell phones, 2 tablets, and the lights for 4 hours. The calculator said I needed a 17Ah battery and a 20W solar panel, but I increased the panel to 30W to help out in less than ideal weather.
Step 2: Drill Holes Through Cooler
We wanted to keep the electronics and battery dry inside the cooler, while providing a way to connect the solar panel, lights, and phone chargers to the battery, so we drilled two 7/8" holes for the solar in and the DC lights out. Using a strain relief provided a watertight through hole for the wire. Because the strain relief was not long enough to go all the way through both layers with the insulation, we cut out the inner layer and insulation to give the ability to put the nut on the back of the strain relief for a watertight connection.
A 1 1/8" hole was drilled for the cigarette socket. This socket was long enough to go all the way through both layers.
Step 3: Mount Charge Controller
In case any water does get into the case, we attached the Morningstar SunGuard charge controller high up on the inside wall.
Step 4: Insert Battery
To prevent the battery from moving around, and for easy carrying, we put the battery in the middle of the cooler, and used scrap wood pieces to hold it in place. By placing the battery in the middle, we balanced the weight for easy carrying. It also created a section for the wiring, and a section for storage of the lights, charger cables, etc to prevent them from getting lost.
Step 5: Wire the System
To help avoid confusion, it is generally recommended to use red wire for positive and black wire for negative in an ungrounded electrical system like this one. We used wire connectors for ease of use, but you could use wire nuts instead.
Follow the schematic to wire the solar panel into the charge controller, the output of the charge controller to the battery, and the battery to the DC lights and cigarette socket. If you don't know how to read a schematic, we included a video to step you through it.
Be careful not to accidentally short across the battery. This applies to tools and hands. There is a lot of energy potential in the battery, be careful. I usually put electrical tape across the battery terminals to prevent accidents.
Ideally, you should have some sort of over current protection, like a fuse or breaker on the battery plus wire. Since this was going to a remote location, we did not use a fuse to prevent them being stuck without a replacement if needed. You can add a fuse or breaker, as large as 10A to it.
Step 6: Attach DC Connectors for Solar and Lights
We wanted to make sure the connectors didn't get crossed or wired backwards, so we used a connector that is keyed to ensure it can only be plugged in one direction. The connector has the negative wire marked with black to further reduce confusion. We also made sure to use the opposite connectors for the solar in and the lights out, so that your only option for plugging them in is the correct one.
Step 7: Wire Long Cable to Solar Panel
Your solar panel can be outside while the rest of your system is inside, so be sure to use wire long enough to reach a sunny spot. Connect the red plus and black minus wires to the solar panel. Connect the other half of the DC connector to the other end. You can use a volt meter to double check that you got the polarity right. If you put the black probe on the - and the red probe on the +, when the solar panel is exposed to light, even from bright inside lights, the voltage should read around +20V. If it is -20V, then you have the wires backwards.
Step 8: Wire the DC Lights
Keeping track of polarity, plus and minus, wire the DC lights to the mating connector. Plug it into the connector and see if they light up.
Step 9: Bring Outside in the Sunlight!
Measure the voltage of the battery with your voltmeter with the solar panel either inside or covered from the sun. Bring at least the solar panel outside and point it to the sun. Measure the voltage of the battery again. It should be a little higher than it was. Once again hide the solar panel from the sun. The voltage of the battery will likely drop a little. If so, the solar panel is properly charging the battery when it is in the sun. Hurrah!
Plugging a standard cell phone car charger into the cigarette socket will provide the ability to charge a phone or tablet, day or night.
We include a video of us testing the the system outside. Enjoy!
For more options to make your system bigger or smaller as needed, check out our website.
Step 10: Optional: Plug in Inverter
If you have items that you need to charge that do not have the ability to plug into a car charger, then you can optionally plug in an inverter instead. Many small inverters come with a cigarette plug on it to plug into your car lighter and AC plugs in the front to plug your device into. Be aware of how many watts you want to power, and make sure the inverter is rated high enough to power it. For example, if I wanted to plug in my 60W laptop, I need to be sure the inverter is over 60W. Also be sure that you calculated for this load when you sized the system, you're not going to power a refrigerator on a whim. The system has to be sized big enough for anything you may be powering.
Have fun with this system. Take it camping, to an off-grid cabin, or anywhere you need a bit of power all day and night.
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