Thursday, September 24, 2020

RV Physics

You can't expect an RV to do things that are beyond the bounds of physics.

We met a nice couple who just bought a new Class-C camper and are very unhappy with it.  It is not that it doesn't work as a camper, but that the promises made by the dealer and perhaps even manufacturer didn't pan out - largely due to the laws of physics.  And since they are not tech-savvy, the couple is unhappy and unable to understand why their coach can't do the impossible.

The industry is partly to blame - selling the idea that RVs can do things that, while theoretically are possible, are practically impossible.   For example, I noted before that the furnaces in RVs work as advertised - they heat up the inside of the camper.  But with twin 20-lb propane tanks, they won't heat it up for very long.   Run the furnace at 72 degrees overnight, and you may wake up to two empty tanks and a refrigerator with a "check" light lit.   You spend the morning trying to find a propane tank exchange place that is open.

Sure, you could "upgrade" to 30-lb tanks, but that just forestalls the inevitable, and makes it so you can't use those propane tank exchange places (which are often the only places to get propane in some parts).  Campers who stay in one place for the season will call a local propane company and have a "snowman" propane tank delivered and hooked up, so they don't run out like this.

So yea, the furnace works, but in a practical sense, it isn't like the furnace in your home, where you can just set the temperature and be warm.   At best, you can use it to "take the chill off" to warm up before bed, or to keep the place from completely freezing.   In the cold weather we have been having (28 degrees yesterday morning) we have the thermostat set at 45 degrees - because we know, realistically, what to expect from these furnaces, after 30+ years and five RVs.  Even so, we've had to go find propane as it sucks one of the tanks dry.

Another "it works but it doesn't work" deals is the idea that you can put a bank of batteries in an RV and then, using an inverter, run your air conditioner or television when you are "off the grid".  In theory, this should work.  In theory.  And this is where the couple was upset.   The coach had four 12V AGM batteries and a solar panel.   If you run an inverter from those batteries, you'd run them dry pretty much in an hour or so, if you have any kind of load at all.

When we bought the Escape,we ordered it with two 6-volt golf-car batteries (in series) to provide more capacity when boondocking.  The guy who did the pre-delivery asked us, "Why did you get the solar panel?" and I told him, "Mainly to keep the batteries charged in storage and to provide extra charging when dry-camping."   He replied, "OK, then.  You'll do just fine."

You see, a lot of people think a 4'x4' solar panel is going to run the air conditioner. I kid you not.  We saw a nice bearded man who probably was more at home in (liberal arts) academia, explain to his friend that, "The solar panel runs the generator, I think" on his new motorhome.  He had this piece of equipment but no idea how it worked (the generator runs on gasoline or diesel - duh!).

In order to run serious home appliances from a battery, you'd really need a Lithium-Ion battery pack from a Toyota Prius or a Tesla.  And some RVs are starting to experiment with this idea and it may have promise.  But conventional lead-acid batteries?   It just isn't happening.  The energy density is just way too low.

But even with a Tesla battery, there is a problem - getting it charged.  We met a nice couple who bought a used Tesla model-S - nearly seven years old!  Hard to believe they have been making them that long.  It still ran and worked well, but charging it was always an issue.  If you had access to a "supercharging" station and had time for lunch, it was not a problem.  But we were in a rural campground in West Virginia with only 20-amp 110V service.   They had to leave the Tesla plugged in to a wall outlet the whole time they were there.

It would be like trying to fill a tanker truck with a garden hose.  Yes, you can do it - but it may take a day or more.  Using a fire hose, it may take only an hour.  So even if you installed a Tesla battery in your RV - and used it to run the A/C and whatnot - the problem would be in keeping it charged.  The coach engine or generator couldn't charge the battery faster than it was draining, and anything other than 50 Amp, 220V service would be insufficient to charge it rapidly enough.  Maybe that explains why the motorcoach set is so paranoid about not having 50-amp service.

So the couple was upset because this bank of batteries took a long time to charge.   Charging from the motorhome engine is problematic.  Even with a heavy-duty alternator, it could take some time to charge these batteries, particularly from dead, even assuming you had a 50 amp wire running from the alternator - which they didn't, of course.  At most, maybe a 10-gauge wire giving you 10 amps or so.  And likely it would burn out the alternator, eventually.  (We noted that the Escape is not wired to charge from the truck electrical system, and after going through alternators in the old F150 and the X5, perhaps I see why).

I also suspect that the power supply (the power panel with 12V charging circuit) isn't sufficient for the battery load.   I put a huge battery in the Casita, and eventually, the power supply failed.  I put a new one in - a small one - and it struggled to handle such a large battery.  Lesson learned - never try to fill a tanker truck with a garden hose.  You'd think an electrical engineer would figure that out pretty quickly, eh?  Well, it took me a while.  Sometimes it doesn't pay to be cheap.

Oddly enough, the "solution" to their problem might be in getting rid of two or three of those batteries and just running the coach as a normal RV with one "house" battery to run the lights and control board for the refrigerator.  Use propane for the refrigerator and hot water, and plug in if you want air conditioning. Trying to make a setup that defies the laws of physics "work" is just an exercise in frustration.  And they were frustrated.

Camping off-the-grid in the last few weeks has been interesting.  When we are in direct sunlight, the solar panel keeps the batteries charged.  But most campsites are in the shade, and the panel puts out fractions of an amp in those conditions.    After several days of no sunlight, we are forced to start up the generator, as the batteries approach that 10V level where things stop working.  Bear in mind, we are only using the 12V system to power the lights and the control board for the refrigerator, and perhaps charge our cell phones.   That's enough to drain two golf cart batteries in a matter of days.  Now imagine running the refrigerator or the A/C unit off them - you'd drain them in minutes.

It's basic physics.   And it cannot be denied.  And unfortunately,the RV industry has been making a lot of promises that the laws of physics can't fulfill.   The bank-of-batteries approach to camping is a flawed idea, unless you have some super-duper way of recharging them, again and again.  A car alternator or a 20-amp plug, or a Honda eu2000i generator isn't going to cut it.

I felt sorry for the couple - they had a nice coach and were very unhappy with it because it was promised to do things that really are not practical to do.   If they just accepted it as a regular RV, they would be happy.  But I suspect there are other issues involved - that usually is the case with buyer's remorse.