I put together a robust portable solar
charging system to extend boondocking
ability. It is most likely overkill, but should have some functionality under less than ideal conditions. I tried to keep all voltage drops under 2 %, which required heavier conductors than what most folks would like to handle. The panels I went with are Renogy 100W, and measure about 47" x 21" and weigh about 16lbs. I fabricated "kikstands" that prop the panels at infinite angles to optimize collection of rays. I decided to leave the panels separated from one another to add flexibility in positioning choices.
The MPPT controller is mounted at the trailer tongue in a NEMA enclosure for weather protection. There was no desirable interior space for the controller in the 16' Scamp
. By mounting the controller at the trailer instead of at the panels meant that the 30’ long wire run could be of lighter gauge. I selected 8/2 marine cable for that run which should keep the voltage loss near 2%, and is still flexible and easy to coil and handle. I used the MC4 connectors at the panel end, as that is industry standard, and weather proof. At the controller end I selected Anderson Powerpole connectors which can be connected under load and are beefy.
Inside the controller box I mounted a Midnite Solar
baby box which houses a 50 A breaker that serves as a battery
disconnect and fuse. Also in the baby box are 2 10 amp breakers which protect the panel wiring and act as disconnects for the panels. I also mounted the Trimetric meter shunt in the NEMA box to get it out of the weather. The components in the box create heat, so I cut a hole in the bottom of the box and fabbed a bug screen and frame to allow cooling air in, and drilled a couple of 2” holes in the top of the box to let the hot air out. I kludged up some weatherproof vent covers out of PVC building weatherheads that should be functional, but ugly. My tig welder is possessed with demons, so I couldn’t fab a sexy vent from aluminum. Maybe later? The wire from the controller to the battery
is about 5’ long, so 4ga. Is adequate with little drop.
The night I finished the system I turned on the Fantastic fan and let it run all night on high and when I went out the next morning at about 10 AM the battery
was down to 75%. The sky was completely overcast and gray. I had only one panel wired due to one defective MC4 connector, so I put the finished one outside and hooked it up. The Trimetric read only 12.8v and 2 amps. I left it for a couple of hours while I worked to repair the other connector. Once the repair was complete I put the other panel out and took another reading. Voltage still dismal, amperage 4, percent of charge 78%. We got 3% from the one panel with only 12.8v! By 2 PM the panels were totally shaded and not doing anything, so I put them to bed. We were only 82%. There just wasn’t any sun showing that day. The next day I Put the Panels out at about 11 AM. The sky was very cloudy, but the sun would break through at times. When the sun shown I would see 14.8V and 13A. Clouds would lower the numbers considerably. By 2 PM the sun went away and I removed the panels. In 3 hours it harvested enough juice to reach 97% charge from 87%. I think this system will be able to bring back the battery from the previous evenings draw, even if the sun is hiding. I have yet to use the furnace
and CPAP all evening, but would like that option. I’ll do some testing at home to see how it does and report back.