Tag: Solar

A few months back I had purchased a new enclosure to hold the guts of the solar box. The original plastic ammo can was beginning to show fatigue at the bottom from lifting the box with the battery installed within. This wasn’t going to be good for a permanent field deployment of this box in the future, so I decided to upgrade to a Nanuk 905 to house everything. This upgrade benefits the project in two ways: Firstly, the thing is waterproof and extremely durable. Secondly, it allows for the installation of a secondary battery in parallel with the one already installed (as mentioned in a prior post).

Two issues with the new enclosure were how to charge the batteries without running the cables through an open lid and how to prevent the batteries from smashing all over the place when the box is being carried (the handle is on the side when laying on the ground vs. the ammo can having the handle on top of the lid).

I solved the first issue by drilling a 1″ hole through the side of the case and installing a weatherproof surface mount SAE socket with the included 4 screws and some black RTV sealant to retain some level of waterproofness.

The second issue was corrected by fabricating an aluminum frame to fit within the case. I was going to make it fit the full interior dimensions of the case, but the interior isn’t flat. The batteries sit side-by-side in the frame and are secured to it with 1″ wide Velcro straps. The edges are all curved inside. The finished product isn’t perfectly square, but it’s fairly close (and dare I say, not too bad for a first attempt at something like this). The only issue with not being fully square is that that the batteries are wedged together on one end. Not a deal breaker, but won’t be optimal when the warmer weather rolls around again.

I decided to instead make a frame that fit the dimensions of the outer part of the foam insert. This should allow for some slight shock resistance to anything inside and also some slight insulation to boot.

I added a standoff to prevent everything from sliding towards the lid when carried by the handle which seems to be working well so far, but it looks like a second one will need to be added on the side closest to the lid hinge. If carried at a normal walking pace by the handle, there is minimal movement of the battery/frame combination as is.

Further steps for this project include beefing up the battery section of the frame with some aluminum bar stock so that the batteries can be strapped down independent of one another which should be good if only one battery is needed for operation (most likely during the summer months where less power is needed). I’m also planning on mounting the charge controller to the inside of the lid using a piece of aluminum bar stock to keep it out of the way when the repeater and radio are installed later on. Another hole will also need to be drilled to run the antenna feedline out of the box, but I’m still researching how that will be done (possibly using a cable gland and sealed with RTV sealant).

A quick little update on this project.

I left the solar box outside for 3 weeks from January to February 2021, seemingly the coldest part of the winter. Temperatures dipped to -23 Celsius at the lowest without the wind chill.

In order to give the box something to do, I hooked up a USB reading lamp to the 12V USB adapter. It wasn’t pulling a crazy amount of power (only 0.05A). The kit managed to keep going, discharging a bit each night and recharging during the few hours of sunlight it had during the day. One handy thing about the light being hooked up was that I could see if the kit was still on without having to go outside.

It only died once that I’m aware of and the next day it came back to life after a few hours of sunlight hitting the panel. That was 2 days before I brought it back inside.

The battery was not able to fully charge each day due to a combination of the cold, some heavy snowfall and overcast days during those 3 weeks. On a sunny day, the sun was hitting the panel for about 3-4 hours per day, which would normally be enough to fully charge the 7A battery during the warmer months, but not enough in the winter. I could’ve adjusted the charge controller to have a higher float voltage to compensate for the cold temperatures (currently set at 14.1 V). The only problem with this is that I would have to manually adjust it anytime the ambient temperature got too high. Not much of an issue in this situation, but it would be an issue if this was deployed throughout multiple seasons (ie: 6 months from January to June). 14.1 V is a good float voltage for 20ish degree weather. Setting it higher to compensate for the cold winter weather would keep it topped up better in the winter, but would lead to the acid in the battery boiling during the warmer months, thereby killing the battery.

My initial thoughts about increasing the amperage by adding another battery in parallel would possibly prevent the float voltage adjustment from being necessary in such situations.

When I brought the kit back inside, the battery was not fully charged. Charging it with the solar panel in the window for about a month did not do much to bring the battery back up to full capacity. It did get really warm here over the last few weeks and so I set it back up outside. Within a few hours, the battery was fully topped off again.