Energy systems in TT's

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Oct 25, 2012
So from what I am reading, propane tanks and 30 amp plugs are the sources to power TT's. It seems there is some redundancy, some appliances can use both depending upon what is available. If this is the case, will it just be larger energy users like fridge, ac? Is this marked on the units in question? I am assuming there is an alternator on the TT someplace to recharge batteries when moving? Is there really any way to estimate how long a tank of Propane will last, given certain loads (some kind of rating or something), or is experience really the only way to learn that? How about refridgerators, is there some rule of thumb on how much energy they would use during normal operations? How many batteries could you reasonably expect to have on a 30' TT (I hate to ask for an average, so just looking for an idea really) and if you upgrade that would oyu have to upgrade your battery charger as well? If you are drawing a lot of current and are on shore power, will your system draw additional current from the battery array?

Is there a general design to eletrical/propane systems in a TT, or is it so different according to make/model that generalities are pretty pointless?

LOL, is there a library post on basic TT energy systems that I missed? If so, feel free to smack me on the snout with a rolled up newspaper, if you can point me at what I evidently missed on my last perusal.

Thanks very much, y'all.

Edit: don't know how I missed the Elec section last time. Am reading through and finding some answers there. Not all, however.
There are things that only run on 110 power and you need to be plugged into a power grid or generator.  These are the air conditioner, microwave oven, hair dryers, etc.  Essentially anything that plugs into a 110 outlet.

The refrigerator will run on electric or gas but it needs a charged battery to function on gas.  It uses energy from the battery to ignite the gas to run the refrigerator.

The lights  and the furnace fan are 12 volt DC. and are powered by the battery when not hooked up to the power grid or a generator. But when hooked up to the power grid or generator, the TT converter will provide 12 VDC to the lights  and furnace fan and recharge the battery.  The furnace uses gas to generate the actual heat.  The furnace fan must run fast enough to move an internal switch or the furnace gas will not ignite.  Therefore, when a battery becomes discharged, there may not be enough power to operate the furnace.  A single battery typical of what is installed on most TTs, will not operate a furnace for more thanone evening if it is fairly cold.

The TT does not have an alternator to recharge the battery.  It may be that the tow vehicle will recharge the TT battery while underway but it depends on how your tow vehicle and TT are wired together.
Lowell's explanation is very good, but I would suggest one change. Everyplace that he said "shore power or generator," read it as "shore power or generator or inverter."

Several articles in the forum Library will help you, though none are exhaustive on electrical matters. The best is this one, RV Electrical Systems.

You probably want to read through most all the articles in the Library section titled "Newcomers Need To Know", plus articles in the section titled "Electrical Power Systems & Hook-ups" and "Batteries and 12v Stuff" and "Fresh Water Systems".  They will probably generate as many questions as answers, but you will be learning.
I will add that your refridgerator when running on propane actually uses very little energy.  We typically run our fridge on propane only when either boondocking or when on a 30amp instead of a 50amp hookup when we're in a full service campground or RV park.

Your use of the term "redundancy" isn't completely accurate.  The dual systems for things like water heater and fridge aren't there in case of failure, they're there more for convenience.  Although if you have questionable shore power they can come in real handy.
Foto-n-T has a point there...

Like the water heater if you run both electric and gas you have a better recovery time and could have a nice long shower.

As for figuring out propane usage there should be a BTU tag on most appliances so you could use a bit of math and figure out the propane usage rate. I'm sure one of the guru's here has the formula.

As for fridge I can tell you with a full charged battery the fridge can run on propane for up to 2 weeks without a problem battery wise. Propane wise it can clear a month on 20# propane bottle. 
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