Sunday, November 20, 2016

A Lighter Dinette Table (Baltic Birch Ply Instead of MDF and Formica)

The stock dinette table weighed a lot -- I think around 30 pounds.  Very awkward to lift when making the bed at night!  So I fabricated a lighter version, using half-inch Baltic Birch plywood.  I finished it with three coats of a wipe-on polyurethane.  We've been using it for over a year, and it has held up well.  It's about half as heavy.

Here is what it looks like when set up for dining:

This is an overview (underview?) of the underside:

And this is a close-up of the socket -- I glued a circular pad of plywood under the table and then screwed the socket into the pad, so that the screws would not come through the tabletop:

Tuesday, November 1, 2016

How to test the working capacity of the batteries

I have two group 31 12V marine deep cycle batteries, which supposedly have a total capacity of 110 amp hours.  In the real world, that means that they have a theoretical working capacity of only 55 amp hours, since I am told that it is not good to draw the battery down below a 50 percent state of charge.  When the measured voltage gets down to 12.1, that's a 50 percent state of charge.

So I wanted to see if I really have 55 amp hours available.  That information is useful for a couple of different reasons: first, if I do have that much available, that tells me that my usual battery maintenance routines are adequate.  If I don't, I have to do something different.  And this reading provides me with a baseline, so that I can tell when the batteries are starting to get old.  Finally, if there is a material difference between my two batteries, that would be interesting, since they were purchased at exactly the same time and have been used in exactly the same way.

(As you'll see below, the results were not what I was expecting.  Hint: this story turns out well.)

My overall plan was to hook up a lamp and then to see how long it took to draw the battery down to roughly 12.1.

I started with a fully charged battery  (which reads 12.9 V when it comes off the charger) and then let it rest for a day, so that the initial reading was 12.7 volts. 

I then hooked up a 60 watt incandescent bulb, plugged into a small inverter, which was plugged into a "cigarette lighter socket" adapter, which has alligator clips that go to the battery terminals.  (If you don't have one of those adapters, they are really handy when you want to hook a 12 V appliance directly to a battery.)  I then used my multimeter to find out how much current the bulb and the inverter were drawing, which was 6.1 amps.

(If you already know how to measure the amount of current that a device is using, skip this paragraph.)  Put the red (positive) multimeter plug into the "10 amp" socket on the front of the multimeter.  Turn the multimeter on to the 10 amp setting. It should read "zero."  With the lamp still plugged into the adapter, unhook the cigarette lighter adapter's black alligator clip from the negative terminal of the battery.  Touch the multimeter's black lead to the negative terminal.  Touch the multimeter's red lead to the unhooked black alligator clip on the cigarette lighter adapter.  The meter will display the amperage.

I left the light on for two hours, thus consuming 12.2 amp hours. I unplugged the light and let the battery rest before taking a reading.  I was told that it had to rest for two hours to settle down.  But I discovered that after a half hour of rest, the voltage had plateaued and did not change.  So for the rest of the experiment, I let the light run for two hours, followed by a half hour of rest, at which point I measured the voltage and then plugged the light in again.
Here are the results in a crude graphical format:













Time            2hr      4hr          6hr          8hr       10hr      

So this means that after ten hours of actual run-time (consuming 61 amp hours), the battery got down to 12.2 volts, i.e., with 60 percent of capacity still remaining.  By extrapolating from this straight-line graph, it looks like I could have gone two more hours, for a total working capacity of 67 amp hours.

That is a lot better than the 55 amp hours of working capacity than I was expecting!

I did this experiment twice, once with each battery, and got exactly the same results.  This tells me that this wasn't a fluke.

I am not sure how it is possible that my batteries are outperforming their rated capacity, but I'm not complaining.  This won't change my consumption patterns when we are camping – we are very careful about electricity.  But this is encouraging news, and it gives me a baseline for subsequent comparisons.


Tuesday, July 12, 2016

Magnetic "Door Halfway Open" Holder

Whenever we cook (which is twice a day), we have to open the windows and the door in order to get enough air – otherwise, the propane/carbon monoxide alarm goes off.  In warm, dry weather, that's no problem – we just open the front door all the way, we step outside, and we latch it open.  But in cold or wet weather, I would prefer not to have to go outside, and we often don't want the door open all the way.  But there is no latch for holding the door open halfway.

So I came up with a rather simple "Mickey Mouse" solution.  I mounted very strong magnets on either side of a short strip of flexible steel.  One magnet attaches to the bolt assembly on the door, and the other magnet attaches to the strike plate.  Here's what it looks like when deployed:

The magnets are neodymium or rare earth magnets, salvaged from old computer hard drives.  (I have a friend in the computer business, but I would bet that you can get these things from any local computer repair shop.)  The magnets have holes in the mounting brackets; using a drill press and some care, it is possible to enlarge the holes to accommodate very small machine screws.

I used a mallet to flatten out a 1 foot strip of galvanized roof flashing.  I then drilled holes for the magnets and put them on either side of the steel strip:

Note that on one side, I mounted a small piece of wood, just to keep the strip of steel from flexing too much.

I then added an extra piece of perforated steel to the inside of the door frame, above the existing bolt assembly -- this is to provide more surface area for the magnet to grab onto: 

It was necessary to use a flexible steel strip, rather than something more substantial, because the bolt assembly on the doorframe and the strike plate are not exactly in the same plane.  So each end of the steel strip flexes slightly, to accommodate this minor disparity:

The whole thing can be deployed from inside the trailer:  I open the little hatch in the screen door next to the latch.  I stick the far end of the holder out onto the bolt assembly.  I then attach the near end of the holder onto the strike plate.  Here is what it looks like from the inside:

These killer magnets seem to be strong enough to hold the door in place, even in a fairly good wind.  But I haven't field-tested this yet, so we will see how it does in the typical strong afternoon Sierra breeze.

Finally, for storage, I screwed a small piece of perforated steel on the inside wall of the trailer, next to the front door frame.  The magnet sticks firmly onto that little piece of steel.

Sunday, November 29, 2015

Manual fresh water tank heater: just a hose from the hot water faucet to the tank, but it keeps the pipes from freezing

During our last trip to Sequoia, the outlet hose leading from the water tank to the pump froze one night, when the temp got down to 11 degrees.  When we got home, I rigged up this simple solution:  A hose connects to the water faucet.  The hose runs to the outside through the outdoor shower opening.  The hose runs along the outside wall of the trailer, and the end goes into the external fill pipe of the water tank.  We run a few gallons of hot water, and the temp of the tank is substantially increased.  The warmed-up water runs through the outlet hose and back to the pump.

Here are some photos:

This is the end that screws onto the faucet – I have included a swivel fitting to make it easier to attach:

Here it is attached to the faucet:

The hose runs over the edge of the sink, under the counter, and into the opening for the outdoor shower:

This is a larger view of the hose as it passes through the outdoor shower opening:

This is an exterior view, showing the hose emerging from the outdoor shower opening – I have also inserted tightly-fitting foam blocks into the outdoor shower fixture as extra insulation:

And here is the hose going into the external fill pipe door:

For storage, the whole thing coils up and goes into an under-seat storage bin.

Some thoughts and caveats:

A thermostatically controlled built-in under-counter system would be far better.  But it requires cutting into the plumbing, and some electrical work.  My solution is crude but effective -- very simple and inexpensive.  It does the job, especially if (like us) you rarely camp in weather below 20 degrees.  (We have camped at 20 many times, with no freeze, but this last trip was just a little too cold.)

Obviously, this solution only works if you have an outside shower fixture -- otherwise, how would you get the hose through the wall?  And it is much easier if you have previously removed all of the outdoor shower plumbing fixtures.  (We did that when we got the trailer, because it is always too cold for a late afternoon outside shower when we are boondocking.  We needed the extra room under the sink more than we needed the shower, since we use the inside shower.)

The main drawback to this system is that it has to be set up whenever you want to use it and then taken down whenever you want to change your campsite.  But we so rarely encounter temperatures below 20 that this will be an infrequent event.

The other drawback is that this system does not operate automatically, unlike thermostatically controlled hot water recirculators.  So, for example, I plan on running this device at least once during the night, which will mean that when I get up at 3 am (which I always do), I will have to stand there for three minutes while the hot water runs into the fresh water tank.  Not a deal-breaker, but not effortless, either.  And the water heater will need to stay on during the entire night, which means that it will cycle on and off every few hours, which is a little noisy.  Better than frozen pipes, though!

Saturday, April 11, 2015

Astroturf on the step bars

Very simple -- a strip of astroturf on the step bar, secured with heavy duty cable ties.  Since we often travel in the mud/snow/dirt/dust, this keeps the truck a little cleaner -- just wipe one boot, hop in, wipe the other, and away we go:

Monday, August 11, 2014

"Half-open" position for exit window with hinged rod

The emergency exit window on the left side of our trailer has just two positions:  fully open or fully closed.  That’s because the window swings outward when pushed by a rod -- there is no “halfway” position.  But sometimes, it would be nice to have the window open just a little, rather than completely closed or open all the way.

The solution is a rod that hinges in the middle.  I happened to have a hinged brass lid support, which is used to hold open a cedar chest.  It has a friction locking mechanism.  (These are sold in many hardware stores -- just Google "locking brass lid support.")   Here is a picture of the original rigid window opening rod and the hinged brass lid support, prior to modifications:

Using the hinged rod and some aluminum stock, I fashioned an exact replica of the original rod.  Here it is in its fully extended position, so that the window can open all the way:

The underside at the end of the rod (near my thumb in the preceding photo) has a channel, which sits on the window sill to hold the rod in position.  The channel is made up of two pieces of thin aluminum stock, riveted to the handle.  The rivets are also aluminum and were pounded flat so that the handle can still pass all the way through the opening in the window -- when the window is used as an emergency exit, the screen pops off, the handle pushes through and out, and the occupants gracefully vault through the swinging window.  (I hope I never have to pass that test of agility.)

Here is the rod when partly folded:

And here it is when secured in the half-open position.  The cable tie slips over the hinged section of the rod to hold the rod in that position:

And here is the rod when the window is fully closed -- the end of the rod is held by the original black plastic clip, attached to the window frame:

Saturday, July 26, 2014

Tripod supports for stabilizer jacks

Since I flipped my axles for extra ground clearance, my stabilizers don’t reach the ground; I usually bring a stack of big wooden blocks to make up the difference.  But the blocks are a little bit unsteady.  So I made some collapsible tripods, and they really get the job done.

They are 16 inches high, with legs made of 1 3/8” closet pole dowels.  Both ends of each dowel are rounded.  The base is made up of four pieces of 8x8 3/4” plywood squares, screwed together to make a block three inches thick.  Using a 1 3/8” Forstner bit and a drill press, I drilled three holes in the block, angled at 30 degrees.  The legs slip into the holes, and the whole thing is easily disassembled for storage and transport.

Here is what it looks like in action:

Here is the bottom of the base block, showing the slanted holes:

Here is a side view of the block:

We used it in soft soil, rocky soil, and on pavement, and it worked perfectly.  Since the tripod is higher than the blocks but does not wobble at all, the stabilizer jack is not overextended and seems to provide much better support and stability.