I’ve already published my blog post about our shakedown camping trip, but I have a bunch more work from right before that, which I have not shared yet. So, this is the post for those photos!
The final piece of the outside skin to attach is the roof. The top of the roof is 2 pieces, a 4 foot section over the main top and a 2 foot section against the galley hinge. The 4 foot section needed a slight bend (5 degrees maybe) in the middle. The 2 foot section is simply flat.
Clamping is the thing… The further I’ve gone on this project, the better I’ve gotten at finding ways to clamp the skin. I also started planning to use screw fasteners.
I used a combinations of pipe clamps, straps and weights to hold the roof down.
Once this had set, I trimmed the edges using the router. At some point I had chipped one of the carbide edges on my flush cutting bit. Luckily, it is only on one of the sides and at the top where I don’t normally cut. I think this happened when I dropped the bit.
Rear Hatch Trim
After securing the skin on the rear hatch, it was time to attach the edge trim that allows the rear hatch to seal. It’s a “T” profile. Screws hold it to the edge of the hatch.
I don’t have pictures after this point because frankly, I screwed it up and got distracted trying to recover from it so we could go camping.
There are 2 things I did wrong. 1st, I butted the top of the trim against the bottom edge of the hinge. I should have cut the flange back to allow the edge trim to go all the way to the top of the hatch.
The second thing I did was cut the lower corner miter backwards. The “T” molding is asymmetric so I couldn’t just swap it to the other side.
At this point I was down to the wire with no time to order replacement. The work around was to attach the trim as best I could and redo it later (still TBD). It mostly seals. So it goes.
The doors and walls are built up from plywood. Before I exposed the trailer to any real weather, I wanted to seal them with some paint. This was a temporary step and will get redone, possibly with additional door/jam milling for better sealing and fit.
At some point after this I installed the EDM seals, which later got pulled out by the door itself. The clearances are too tight. I’m already in the process of remilling them and using a silicone seal which should hold up better.
Rear Hatch Support & Seals
The rear hatch on this trailer is pretty heavy. 100lb 21 inch gas struts won’t lift it. Nor would 130lb (the heaviest I could find). There is no configuration where they have enough mechanical advantage to support the weight. Longer struts might but then I have to start worrying about interference with the counter top and other elements.
You can see the struts installed here, as well as the trim and seal on the outer wall.
See, that degree in math (which involved an awful lot of calculus and differential equations) comes in handy… I can just about handle trig still from memory. The goal is to have the strut pressing up at 90 degrees from the hinge-strut-mount-line on the trailer.
Why? Intuition, but also, it fits best that way, and the math is easier since it is a right angle triangle then. And, the 90 degree angle move the mount point as far from the hinge as possible with this length strut. The short struts have to be pretty close to the hinge regardless. A longer strut would be farther from the hinge, and have a greater mechanical advantage (or less disadvantage).
The hatch doesn’t weight anything like 200lb (2 times 100lb struts). It probably weights about 60lb. But, the strut is having the lift it from very near the hinge. Most of that weight is hanging out past where the struts are lifting. Think levers, one short (where the strut is lifting) and one long (the weight of the hatch out past the strut). It’s like opening a door by pushing on it near the hinges. It’s hard if you can do it at all. If you push on the other side a long way from the hinges it opens easily… Same problem here.
I opted for low tech to solve the problem. The gas struts make it easy to open and close the lid but won’t hold it up. A stick holds it up. There are pictures of that in the shake down post.
Here you can see how the hatch edge trim is attached, and also the galley lights turned on.
Before I launch into this, if you don’t care about wiring, you are probably just about done. This section is long, about angry pixies and is a little dry. It will probably sound like gibberish unless you know a little about electricity/wiring/electronics. I need to add some diagrams and such. I will be doing a real complete post just about the electrical eventually. For now… this is what I got.
One of the other major punch list items was to connect up the wiring. It’s not a very photogenic process, but I took a picture of the semi-finished panel (all wired and working, but the supply isn’t wired in for real).
A word (several in fact) about the design of the wiring. I ran common 12V lines (all the white wires) to the various locations. You can see these all connected up on the lower left corner being supplied by a single 5 amp fuse for now.
The line runs from the fuse block and daisy chains to all the terminals on that block. That is the supply side. In the middle of the 2 rows of terminal blocks is the trailer side. The white lines are under everything else, so not obvious.
All circuits are connected to 12V+ all the time. Many of the lights on the trailer share 12V+ lines. There is approximately one 14 awg line per area of the trailer (rear hatch, left wall, right wall, ceiling).
Ground Home Runs
I ran home runs for the ground (-) side of each light fixture. That means each fixture has one 14 awg line back to the wiring box. The ground sides are the colorful lines (blue, purple, orange and yellow). The lower right and upper left terminal blocks are where the trailer side of all these home-runs terminate. Note the upper left where the wires on the left hand side of go out a hole above it to part of the trailer.
The 4th terminal block (upper right) is the switch interconnect. I haven’t talked about how the switches in the trailer are wired yet… Lets do that now.
The trailer has 3 switch locations: one by each door and one in the galley. Each switch location has a 3 switch unit. The switches I used are standard 110V household switches designed for high voltage and household loads (5 to 15 amps, so about 550 to 1650 watts per switch). We’ll come back to this in a minute.
Each switch box has a run of 5 conductor wire (the brown bundles that split into the smaller wires) normally used for wiring household thermostats (which are 12v systems, which is what this is). I used the same color convention on all switches, but I can’t remember what it is now. Regardless, 1 wire is the “common” wire hooked to the ground block (bottom most terminal on the upper right terminal block).
When a switch is turned on, it connects this common wire (12V ground) to one of the other 4 wires in the bundle. So, I can configured which light (or lights) a given switch controls by wiring the home run from it (the color wires connected to the upper left and lower right terminal blocks) to that switch’s wire (upper right terminal block). When the switch is on, the switch wire is grounded, completing the circuit since 12V + is always connected.
Does all this seem over complicated? It isn’t but explaining it in text is slow. I could have just wired this all up fixed by running either the positive 12V or negative 12V through the switch and to the lights I wanted it to control. That would have left me no flexibility.
With this setup, I can simply “patch” any light to any switch by cross connecting the right terminals. Really, I wired this similar to how a phone junction or network junction is wired.
That said, this also allows me the freedom to complete a future planned project: automation via an app and a Arduino and/or Raspbery Pi. With that automation, I can patch the switches to digital input pins, and the light home run ground lines to output pins (via transistors or relays). I can then make the switches “smart”. I can make them operate like three ways. Or I can interpret multiple toggles to dim a given light. I can also set “modes”. The app can trigger “disco mode” or “late night mode” or whatever.
This is also the reason I am switching the ground not 12v+. That is the normal “conventional” way that solid state electronics usually (in my limited experience) switch loads. It shouldn’t make any difference (either side of the circuit sees the same current – because it is circuit) but that seems to be the convention.
Anyway, that’s down the road. The goal for this stage was to keep that flexibility, keep it serviceable and understandable (for me) and get it working.
I’m not a EE, nor an electrician, but I know enough to be dangerous (or rather, to avoid danger with low voltage anyway). What we’ve talked about so far is all 12V, and all very low current. The single fuse that runs the entire lighting system is ONLY 5 amps, and it could be 3 amps probably.
Supplying Angry Pixies
The trailer has a 12V power supply (industrial) installed in the front cabinet as well (not pictured). I don’t remember the exact wattage it can provide, but it was about 2x the load that having all the lights on at once could possibly draw.
It is fed off the 110v circuit (which I haven’t talked about) in the trailer, which is all romex in standard household boxes with standard household outlets, installed like it would be in a wall at a home or in conduit.
When off grid, I have a sealed gel cell lead acid battery (again, don’t remember the capacity off hand but it should run the trailer for about 24 hours straight with all the lights on 100%) wired into the 12V circuit. The power supply has it’s output voltage tuned to be roughly 13.5v which is high enough that it should keep the battery charged (works just like an alternator on a car which just pulls the voltage up when the car is running) when the trailer is plugged in.
The battery can act as a brown out buffer should anything ever manage to overdraw the power supply for a few seconds or minutes (which should actually blow the fuse I have in there now, but future proofing…).
As of yet, I have not integrated vehicle power (via the trailer connection) to charge the battery, but I should down the road for off-the-grid use.
Amps and Watts Oh My
The trailers lights are all LED (just about all 3 watts per fixture. Remember the 110V switches are designed for 550 to 1650 watts. Yeah, overkill, but cheap and available and easily installed.
The main concerns are the current carrying capacity of the wire. Standards indicate that the 14 awg stranded wires I used most places can easily carry 5+ amps for runs less than 20 feet (and depending on run length and duration, a lot more). Current carrying capacity is a function of wire cross section, material and run length… The entire trailer is run through a single 5 amp fuse, so, the 14 awg wires shouldn’t be a problem. In fact, it is pretty severe overkill.
The ground side of the circuits uses a much smaller wire (18 awg solid core – the thermostat wiring), but again, at the loads the LEDs require, it is totally fine. Down the road, it won’t even carry load current. It will just twiddle a digital IO pin with megaohm resistance. All the current handling will be via a relay or transistor in the wiring box, not out and back from a switch. Regardless, it works in both cases.