I've been charging 18650 rechargeable batteries from a small 12v battery solar charger for a few months now. Not impressed with the charge rate, spending an entire sunny day only to maybe have a single 18650 battery charged. I decided to step it up a notch & bought a 20w 12v solar panel from an ebay auction. Now I had to decide either to mount the panel outside & run wires into the house or to make it portable. I decided on the latter, as 20w is a bit meager for a rooftop installation.
Researching charge controllers one can quickly see the better ones are MPPT & cost around $100 or more. MPPT's are worth the money if you have a roof-load of solar panels. In this case a very basic charge controller is all that is needed. This 10amp unit is as basic as it gets, & for a paltry $10.
After a lot of research on the web I believe I've come up with a decent portable charger for not a lot of cash.
20W poly solar panel auction price $36.00
10A CMP Solar Panel Charge Controller 12V/24V 10.00
4 x 12v SLA batteries aprrox. $25. ea x 4 = 100.00
DC 9-35V to 5V 30W 6A Car Charger 4-USB Port Step-down Power Supply Module 6.00
5 Digit DC 0-4.3000-33.000V Precision Digital Volt meter 8.00
9 Volt 400mAh Ni-MH 6F22 PP3 Rechargeable Battery 8.00
3amp fuse & holder 5.00
Total cost $200 more or less.
I used the batteries from a computer power backup (UPS) so the cost is nil. Luggage cart, scrap plywood, etc.
Step 1: Wooden frame
Two small pieces of 3/8 or 1/2" plywood screwed together with a 2 x 2" for added support. Size is determined by #1: number of batteries to be carried on base #2: spacing of electronics fastened to backboard & #3: the size of the cart. I used a small frame from a luggage carrier I believe. One small bungee cord holds the back panel to the cart. The weight of the batteries also helps to hold it in place.
Step 2: Batteries
I used 4 x B.B. Battery HR9-12 Valve Regulated Lead Acid (vrla) 12 volt 8.0 amp hour batteries which I found in a computer back-up power supply. These I wired with 12AWG in parallel to maintain the 12 volts & increase the number of amp hours to 32 following the design by ch5 (above) with the battery bank wiring going to the charge controller. The roll of 12AWG cost close to $20 at Home Depot so I only purchased one roll of red, hoping to have enough black wire around the house that I could use. I didn't, so I used the red wire putting black heatshrink on the negative wire ends and some strips of black heatshrink every few inches along the length. Placing a stiff board beneath the 4 batteries they could be lifted all together & placed into a shoebox, which holds them together as one neat package. The 2 wires connecting the batteries to the charge controller are left purposely long to allow the lid of the shoebox to close, the lid creating a small work surface to hold items being charged.
It is important when wiring to the charge controller that the batteries are wired first, the solar panel second, the power out last.
Step 3: Wiring 20w Solar Panel
Thanks to khaleel123 & his drawing "solar controller wiring" (above) found on his instructable Solar Panel Setup around $100 - I was able to wire things up
Found a couple lengths of 14AWG red & black wire to run from the solar panel to controller. To determine the length I wanted to keep it as short as I could. In normal operating mode the aluminum frame of the solar panel will hook onto the top of the plywood. This not only angles the solar panel roughly towards the sun but keeps all the electronics beneath it dry, sheltering stuff from the occasional rain ( I hope!). Otherwise the panel only needs to move from one side to the other to allow access to the electronics.
Step 4: Battery Monitoring
After attaching the pos & neg 14AWG from the battery bank to the charge controller, bringing the controllers leds to life I should add, I felt I needed some way know the state of the batteries. Other than the 3 leds on the face of the charge controller that is. I splurged on a 5 digit voltage meter, roughly 9 bucks. A 9v rechargeable battery is needed to power this little puppy.To fasten this panel to the plywood I used double-sided tape then drilled a hole to each side of it & fed a zip tie through, snugging it up in the rear.
The next step is connecting wires to the power out of the charge controller. Attaching a Barrier Terminal Strip Block with screws to the plywood next to the charge controller. In the positive line going to it I added a 3amp Fuse. This is just a guess as I don't know if 3A is enough so over the next few weeks I'll try to find out the proper value. I think an on/off switch is probably a good idea to include at this juncture also.
Step 5: Using the Harvested Power
Attached a 4 usb port device I snagged off ebay to test the system. It's cloudy out today but definitely noticed some charging before the rain forced me to pull things back inside. Success! Took 2 hours to fully charge my 2100mAh Nokia cellphone from 35%.
Placed an order with BangGood for a 12v/ 2 x usb/ voltage meter (shown above) which I think will fit nicely on here. It has a 12v power point which will allow me to plug in a 300w power inverter. Will a 300w inverter work with a 20w solar panel? Suppose I'll find out.
This project is small enough to take camping or out on a picnic. During a power outage it will keep the laptop, cellphones, flashlight batteries charged so it's definitely worth making just for that.
Hope you find this a worthwhile project. If you have any questions or ideas for improvements do pass them along!
Oh Yeah. I've entered into the MAKE ENERGY: A US-Mexico Innovation Challenge. I'd appreciate a vote. The Buttons' at the top of the page on the right, I do believe.