The detailed design was split into 3 sections, structural, electrical and water.
To design the structure I used a free computer program called google sketchup. This program is basically a user friendly 3d autocad. Taking the constraints of the existing internal structural measurements I set about drawing up the internal structure that would fit the components from the high level design within an aluminum frame. This let me see the layout from a 3d perspective and make any minor adjustments before construction.
Fold down outside kitchen:
Internal bench top view:
I made the height of the fridge framing so that it would line up the fridge top with the 16mm melamine bench top. This would increase the usable bench space.
To design the electrical side of things I relied on my trusty blue book and favorite mechanical pencil. With these in hand I first worked out the number of end points
-1 x Fridge (12v cig outlet)
-1 x 12v cig outlet for a fan, for those steamy nights
-2 power locations; at the camper entry and the inside seats, with an option for a 3rd in the kitchen. Each one of these would have a 12v cig outlet, usb outlets and 240v outlet
-12v water pump
I chose to feed these endpoints from a central switch panel with resetable fuses. The battery guage would also be located here.
To take care of the myriad of charging options I chose the ctek ds250 and smartpass. I coupled this up with a Nasa bm1 compact to act as the battery guage and an AC to DC convertor to charge from mains power. This was against ctek recommendations, they recommended a separate ac charger for ac charging, but I saw this as a double up of charging circuitry and bloody expensive. I cranked the dc output up to 15v and fed it into the solar input on the ds250 as only one of these would be used at any one time.
I also chose to mount all the electrical components on chopping boards which would slide into the space above the batteries. This would also let them be able to slide out for troubleshooting.
The design of the water side of things was the hardest for me. I had no experience in this area and was really shooting from the hip. I was really making it up and wasn’t too sure if it would work or not.
I decided to use a small 12v pump to supply the water from the tank. This needed to be able to self prime, and needed a pressure switch to cycle on and off. The pump would provide potential or pressure to what I thought of as a water ‘bus’ with the water outlets all connecting to this bus. I also wanted to be able to use the pump to pump from other sources into the bus, for example to supply water that had been heated on the stove from a bucket to the shower. This meant that a few interchangeable connections would be needed at the pump.
After looking up the prices of water guages on eBay I quickly talked myself out of installing an electrical water guage and instead relied on some tricks an old mate of mine Bernoulli taught me. I decided to use the 2nd blank water tank outlet to connect to the hole in the top of the water tank and the breather on the filler, this would be with clear plastic hose so that I could see the water level.
With the detailed design done it was time to finalise the bill of materials, get ordering and look forward to demolition.