Originally Posted by Zoinks
A bit of a tangent question. I was told you have to have the propane tanks turned off when driving. I thought the person said it was illegal to have the propane tanks on. Part of why I ask is I have a similar issue but it's with the refrigerator switching from AC to DC. AC on shore power and when I drive I wanted it to automatically switch to DC and I get the check error. I didn't try propane because I thought you could not do that while towing in motion.
Many, if not most, of us run propane on the road. Every jurisdiction is different, but generally restrictions on the use of propane are in tunnels, on ferries, and in other similar circumstances. It's typically legal to run propane on the road. And the tanks have several safety interlocks to prevent spewing huge amounts of gas in the event an accident ruptures a hose or breaks the regulator. (If the tank ruptures, all bets are off, and whether the propane is running or not doesn't change what happens then.
As for running your fridge on 12 volts, you will drain your battery despite being hooked to the tow vehicle (TV). The TV can deliver about 7 amps for charging thru the 7 pin connector. The fridge is making LOTS of heat to transform the ammonia, and heat means BIG amps...often far more than 7 amps, which means you're running a drain on your battery.
If you will connect to shore power at the other end of your trip, and if that trip is not too long, you might be fine on 12 volts for a short period. But, to illustrate, in my original PUP I had a TINY 3 way fridge - not even a freezer. I ran it on 12 volts to a boondock destination and discovered that my battery was substantially drained after only a 4 hour drive! I had to fire up my generator to recharge...an unexpected and unwelcome surprise. I got that bugger running on propane right away and always thereafter on the road.
Your fridge makes heat to cool. Heat production is the enemy of 12 volt battery power. Do not run your fridge on 12 volts unless it's your only option.
One more illustration. I have solar and a small inverter. I use my battery thru an inverter to run a 360 watt electric blanket for about 15 minutes to take the chill off our bed. 360 watts ain't nuthin', yet at 12 volts, 360 watts thru a 120 volt inverter draws more than 30 AMPS
!! 30 amps for an hour is....30 amp hours. A group 24 battery (typical with a new towable) can safely deliver about 35 to 40 amp hours before you start damaging it. THAT'S the 12-volt price of making heat.
Get your fridge running on shore power or propane, and let it run for a few hours. Then go feel the amount of heat pouring out of the top exhaust vent for the fridge. Your 12 volt battery won't make that kind of heat for long before it goes dead.
Last bit of info. A 12 volt group 24 battery is rated at about 70 to 80 amp hours. You get to use half. Let's say 40 amp hours.
Now, by comparison, how much energy is in a tank of propane?
~ One gallon of propane = 91,000 BTU/hr
~ A 20 pound tank of propane holds about 4.5 gallons = 410,000 BTU/hr
~ Convert 410,000 BTU to watts = 120,159 watts
~ Convert 120,159 watts to amps = 10,013 amp hours.
Your battery delivers about 40 amp hours, and just one of your likely two propane tanks delivers about 10,000 amp hours of equivalent energy. If you carry two propane tanks, you have the energy equivalent of 500 of your batteries!!
Run propane whenever possible, unless you have shore power.