Going Solar

Twice during our 2017 camping season we found ourselves consuming soft ice cream and tepid milk as our fridge struggled to deal with the rising temperatures outside.  For this camping season, we made an improvement that we hope will eliminate this problem.

Before I get into the modification, let me first talk a little about RV refrigerators. While some RVs today boast residential fridges, most have what is called an absorption refrigerator.  This type of refrigerator can run off electricity or propane, has no moving parts, and is really a wonder of engineering.

A residential fridge operates by using a coolant and a compressor to create cold air that it then blows into the chamber.  It adds cold to the box. An absorption refrigerator works on the principle that if you remove the heat from a box, what is left will be cold. Using different chemicals with low boiling points and a heat source to move them through the coils, heat is absorbed out of the chamber. Instead of adding cool air, it removes hot air.

Naturally, that heat has to be dissipated in some way or else it will just cycle right back into the fridge.  The exterior wall at the base of an RV fridge has a grate to let air in.  On the roof above the fridge is a vent to let air out.  As the coils absorb heat, the hot air rises, drawing in fresh, hopefully cooler, air from the bottom vent.  Under most conditions, this natural movement of air is sufficient to maintain a cool temperature.

The trick is that if the temperature outside is too high, the system will be unable to dissipate the heat it absorbed and your fridge will not get as cold as you would like.

The solution to this problem is to move air through the coils faster.  This is where our modification comes in.

20180505_102556Our roof vent is fairly typical. Just a cap where air rises and then vents along the edges.  We chose to replace it with a solar-powered Camco vent (part No. 42165).  This vent has a spot to add an additional fan as well, which we did (part no. 42162).  The process to install was to simply remove the old vent, mount the fans and attach the new vent cover.  No problem.

With the old vent off, it reveals a secondary cover with screen mesh protecting it from birds and such.  This mesh is embedded in the plastic, so the only way to remove it was to cut it.  I cut it out using wire cutters, though tin snips likely would have worked as well.  I was careful to leave one loop along the edge of the base so I could re-attach this mesh later.

 

20180505_102607

For some reason, these fans come with pre-installed switches that are about 8 inches from the fan.  Once the install was complete, these switches would basically be inside the wall behind the fridge.  If I left them switched on, the fans would run all the time — even in storage.  This was not acceptable.

20180512_100406Our control panel inside the camper has an unused switch slot in the top right position.  While it is labeled Tank Heater, I figured it would be best to re-purpose it for these fans. I had already installed a separate panel for our tank heater switches so this slot was free for other uses.

Getting the wires from the fans over to the switch panel was not a simple task.  This required removing the microwave, a light under the cabinets and an outlet under the cabinets.  I then needed to use a fish tape to follow the existing wires behind 20180512_143618the pantry and out to the backside of the refrigerator.  I am glossing over it here, but this was a pain in the butt.  It was also totally worth it to get a switch for the fans on the control panel where it belongs.

Since I have two solar panels and two fans, it would generally call for two switches.  I decided to simplify it by connecting everything together in parallel and using a single switch.  The question this presented was, are the fans and wires rated to handle the combined load of two solar panels.  This required from research and testing.

I contacted Camco and they shared that each solar panel is rated to provide 3 Watts.  Checking on message boards, I found that the panels also generate a max of 4 Volts.  Since a Watt is Volts times Amps, I could calculate that the maximum Current generated by one panel is .75 Amps.  Combining the panels would lead to a maximum possible Current of 1.5 Amps.  The wires that came with the kits are 22 AWG.  This is rated for up to 3 Amps so I was well within tolerance.

I then did my own testing to confirm everything.  I did this on an extremely hot day with no clouds.  I wired up the system and measured 4 Volts.  With both panels wired together, the system generated .3 Amps.  So both the Voltage and Amperage were lower than expected.  After this testing, I was confident that the system could handle the load that I would be putting on it if I wired them in parallel to a single switch.

20180512_143326To the left is the wiring diagram I used for connecting everything. The solar panels are on top with the fans below.  The switch is off to the right with wire nuts connecting everything.  I used 18AWG wire for the run to the switch.

With all of this planned out, it was just a simple matter of doing the work. After getting everything in position, I made loose connections to confirm everything functioned as expected.  I then used crimping wire nuts to make the final connections.

20180506_135607The most difficult part of the modification was mounting the fans.  I screwed them into the exterior wall, but it was a chore trying to get my hands down into the opening while holding a screw and a fan and a screwdriver.  After a couple attempts, including one where I just about put a screw through my finger, I changed tactics.

I drilled a 1/16″ pilot hole about where I wanted one screw to go and then screwed in one side of the fan, but not all of the way.  I held the other side of the fan in position and marked where that screw needed to go.  I drilled another pilot hole and added the screw. I then tightened both screws. I repeated the process for the second fan.  The fans have a sticker indicating the direction of air flow.  Make sure they are blowing up.

After securing the wires, it was time to attach the lid.  Of course, this needed its own set of challenges.

W20180512_153212.jpghile the cover indicated that it fits all Dometic fridges, the holes did not line up on my fridge.  Fortunately, the vent came with a bracket that you attach to your base and then the cover lines up with that bracket.  This adapter bracket is the white piece on the mounting base in the picture on the right. Overall, this was a minor inconvenience.

 

20180506_144123After applying a substantial amount of caulk to the screws and solar panel edges, the job was done. We now have solar fridge vent fans in place that can be turned on or off using a switch on our RV control panel.

Hopefully the next time we camp in hot weather we can have frozen ice cream! We’ll keep a close eye on the temperatures during our next camping trip and report back!

 

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