Field operations using batteries are very common and my battery box is a very convenient source of power. For longer term operations, however, keeping the battery charged is just as important. In order to supplement my battery system I put together a small solar charging system.
- 50 Watt, 12V Solar Panel – Renogy
- 10 Amp PWM Solar Charge Controller – Renogy
- 1″ Aluminum Angle
The goal here was to have a simple solar system that would be large enough to charge my battery box at a decent rate, while still being small enough to transport easily. I also wanted to keep the costs fairly low.
I went with a 50 watt solar panel since it is fairly compact (around 2 ft square), inexpensive (about $80), and puts out almost 3 amps at peak sun. The charge controller (under $30) prevents the panel from overcharging the battery when the sun is out and blocks the panel from discharging the battery when the sun goes down. The aluminum angle frame holds the parts permanently together (which simplifies field wiring) in addition to holding the panel at a 30 degree angle. A 30 degree panel angle is a good compromise for my latitude and helps maximize the panel’s sun exposure throughout a full day. All together the panel, controller, and frame weigh about 12 lbs.
I used this setup with my battery box and go kit for Field Day this year and it performed very well. I generally do digital only on Field Day and made over 160 contacts using PSK31 and RTTY with the radio set for 50 watts output. With the sun out, the panel kept up with my power usage and by sunset the battery was essentially fully charged despite me operating for several hours. I continued to operate after sunset and quit around 1AM. I resumed operating mid-morning and the few preceding hours of morning sun had recharged the battery back to near full charge.
As with any battery testing, the current draw is the deciding factor for how long your charge will last. Since Field Day is in many ways a contest I was transmitting quite a bit which increased my current draw compared to more casual operations. Overall I operated around 16 hours and never drained the battery below 12V. If I turned the power down, I could probably operate the entire 24 hours and dropping from 50 to 25 watts would have minimal impact on my ability to make contacts.
Update (June 2018)
Along with upgrading my power box, I also wanted to upgrade my solar charging capability. Since I already had a 50W panel, I decided to buy another of the same size from Renogy and make my own folding 100W panel system. I used basic zinc plated hinges and keep the panels folded using a simple bolt and aluminum plate system. The bolts also provide points to allow the attachment of aluminum legs to keep the panel tilted at a 30 degree angle to pick up maximum sun. I also mounted a comfortable handle to make the panel system easier to carry. The two panels are connected in parallel and then connected to the power box via anderson powerpoles. This allows the panels to charge my 40 Ah lithium iron phosphate battery via the Epic PWRGate inside the power box.
I used this setup during Field Day this year and it worked very well. We had a mix of clouds, sun, and some rain but the panels were capable of keeping up with my HF digital station (running at 50 watts). In full sun these panels will charge the battery with about 6 amps, more than enough to keep up with the radio’s average power usage which is about 3 amps (mostly receiving, transmitting about 25% of the time). This keeps the battery more or less topped off during the day. I didn’t operate all night, but I did put in several hours after the solar panels had stopped producing power. In the morning the panels came to life again and charged the battery back up some even while I was operating. By the time I packed up I still had about 28 Ah left in the battery according to my PWRCheck. Overall I am very happy with my new power box and larger solar panel system.