Propane! ... new full-timer ;)

[BernieD]

I'm really not so sure why all the refer inverter bashing ??? I had our refer put on our inverter circuit when we bought the coach. I prefer having the refer run on electricity when traveling on the highway, the alternator keeps the battery bank full, so there is no drain. When we drycamp it is very easy to push the button to switch to LP only to avoid the battery drain. Not such a big deal.

 

[Ron]

No one is bashing refer inverters hookups Bernie.  Just normally the refer is not connected to the inverter unless requested.  Its one of those things some do and some don't.  When boondocking if one forgets to switch over to gas running the refer on battery will shorten the time between regharging batteries. ;D

 

[Tom]

Interesting Ron. Our refr on the Monaco came wired to the inverter. When we first had the coach, the alternator wasn't charging the house batteries, so they'd die in short order if I switched the refr to AC while going down the highway. When I posed the question here, I received mixed responses, similar to the ones in this topic. When I checked the schematics for the coach, they confirmed that the refr is supposed to be plugged into a duplex running off the inverter, and the house batteries are supposed to be charged from the alternator. It took the factory tech a few minutes to find that a wire had been placed on the wrong terminal of a relay. All now works as intended, although I must admit we often run on propane.

 

[Ron]

Tom,

I have seen coaches wired both ways but most that I have come in contact with close enough to see how they are wired do not have the refer wired to the inverter.  There are some benefits of the refer running off the inverter for sure.  The only down side I can think of is if one didn't know this or just forgot to manually switch over to gas while boondocking.  I have considered placing another outlet in the refer compartment that will have inverter power so I can plug in while traveling.  Just hasn't been very high on the piority list.

 

[Tom]

That's certainly a good reason not to have it wired to the inverter Ron, and maybe that's the subconscious reason I normally run on propane. But, every now and then I think of the potential fire hazard, and switch to AC.

 

[Ron]

The biggest reason I even consider putting a inverter feed outlet in the refer compartment is to keep the ice maker working while on the road. Like I said not a real high priority.

 

[Gary RV_Wizard]

I have my ice maker on an inverter circuit  but not the fridge (the fridge ice maker has its own power plug).  My choice, since I added the inverter myself. That way the ice maker still works when we are boondocking but the automatic ac/gas switch on the fridge handles everything else nicely.  Since I have both types of outlet in the fridge compartment I could easily change the fridge over to an inverter-powered circuit either permanently or when circumstances made it practical, but I have never seen a reason  to do so.    Just my way of doing things and certainly not the only way.

I can see an advantage in the inverter-only approach because you never have to remember to switch the fridge off and then back on when fueling. That trades off against stops that are lengthy enough to make continued cooling powerdesirable, where you have to remeber to switch manually to gas. Perhaps six of one and a half dozen of the other?

 

[Lou Schneider]

recently stopped at a U-Haul and bought two new gauges (that actually work), one each for my 2 propane tanks, and
lo and behold, they were both still reading full!? So you guys aren't kidding when you say they will last a while

What kind of gauge did you get?? ?If it's a pressure gauge, it won't work the way you want.

Propane isn't compressed gas - it's gas that boils off from liquid.? The pressure in a tank of propane will remain constant until all of the liquid propane is gone.? A meter that reads the gas pressure at the tank outlet won't show you how much propane is left in your tank.? ?Liquid propane is something like 200 times more concentrated than the gas, so when the liquid is gone the tank is essentially empty.? ?Since the pressure remains constant until all of the liquid is gone, a pressure gauge can't tell you how much propane is in the tank.

In order to get a real level, you have to replace the whole outlet assembly with one that has a gauge driven by a float extending into the tank.? Is this what you got?

The other type of gauge that is truely accurate is a strip that goes on the outside of the tank.? ?It's made from liquid crystals that change color when you pour hot water over it.? ?Like running your hand along the outside of the tank, the tank (and the strip) will get warmer and change color where there's gas and stay the same color where there's liquid.

 

[Gary RV_Wizard]

The pressure in a tank of propane will remain constant until all of the liquid propane is gone.

Isn't that a little bit overstated, Lou?  The tank pressure will vary some as the liquid propane level goes down, though nowhere near in proportion to the level of the liquid.  And the pressure also varies with ambient temperature (either up or down) or the sun shining on the tank, further complicating things.

I readily agree, though, that pressure-type gauges aren't very reliable propane level  indicators.  Generally they will show FULL until nearly empty and then drop very quickly, giving you little if any warning.

 

[Karl]

Gary and Lou,
You're both right - to a degree. Almost all matter can exist in one of three 'phases' - solid, liquid, and gaseous(vapor). The point at which a solid becomes a liquid is the melting point; the point where a liquid becomes a gas is called the boiling point. It all depends on a combination of temperature and pressure. Interestingly, some substances can exist as a solid, liquid, and vapor all at the same temperature/pressure. This is called the triple point, but is not pertinent to our discussion of propane. If you evacuate a container and then pour in some propane (C3H8), some of the liquid propane will change phases and go from liquid to vapor until equilibrium is reached and it is at this temperature/pressure combination that the process stops. In truth it still continues, but an equal amount of gas returns to the liquid phase, so the net change is zero. At equilibrium you can measure the pressure of the gas in the cylinder, and that is what's called the vapor pressure. At equilibrium, if no additional heat is added or lost and the pressure remains constant (as it would in a closed container like a propane tank) the respective volumes of liquid and gas will remain constant. As you draw the gas off (like turning on a stove burner), the pressure inside the container will drop and more of the liquid will change into the gas phase and the vapor pressure will remain constant.  This is true until there is no more liquid in the tank to change into vapor. At that point, the pressure of the gas being drawn off will continue to drop until it finally equals atmospheric pressure; then flow will stop. It is for these reasons that a pressure gauge is useless for determining the amount of liquid propane remaining in a tank. As Gary mentioned, temperature is one of the variables in determining vapor pressure. If your tank becomes hot, the pressure will increase and force some of the vapor back into the liquid phase. Too much heat, and there won't be much vapor left to convert back to liquid, and the pressure could reach dangerous levels.  Conversly, if you were to travel to a place where the temperature is -108F and had a normal atmospheric pressure, no gas would flow at all because you would be below the boiling point of the propane (-107.1F). I don't think many of us have to worry about that! ;D  There is another temperature/pressure combination referred to as the Critical Point. For propane it is 204F at 609lbs/sq. inch. It is at the critical point where no amount of additional heat or pressure will change the gas back into a liquid. Obviously, the safety pressure relief valves on our tanks are set well below that point.