RV power consumption

[mike_b42]

Just came back from a long weekend in the mountains, and we had a cold night, and in the morning there was not enough power left to run the heater. There was also a prohibition to run the generator early in the morning, so we had to spend a couple of cold hours. WE had the same problem in one of the last outings, but in that case the battery just lasted long enough

That brought up a few questions that I am trying to find an answer to. oes anybody know what the power requirements of the major users are (heating, fridge (on LP gas), lights,...). If I am not mistaken a typical RV battery has a capacity for 100 Ah (at 12V), so about 1.2 KWh. That would run a 12 W light for roughly 100 hours. But how much do the other things use? Is it normal for a battery to be empty in the morning (with some lights on in the evening)?

Also: How long does it take to charge the battery with a generator. I have a 4KW generator, but I don't think I can charge the battery in 20 Minutes. My guess is that the charging current is limited, so running the generator just to recharge the battery so that the heater can run is a colossal waste of energy (and gas).

the second question relates to the batteries themselves. My RV has a lead acid battery. One option to extend the battery life would be to add additional batteries. I have seen some Lithium-Ion batteries advertised. Is it possible to mix lead-acid and LI batteries, or is that a bad idea.

Finally, there are some Uninterruptible Power supplies for computers available that are rated at around 1.5 KW, and they are a lot cheaper than the batteries. Obviously they can't be installed under the RV, but has anybody used them as a backup? Charge them at home, put them in the RV, when the battery is low, plug the shore line into the UPS and use it until it is empty, or until one can fire up the generator. Then the generator has enough power to charge both the battery and the UPS. and when driving the RV, a small portable inverter could be used to recharge the UPS (not the most efficient way: create 12V, convert to 110, reduce to 12 V to recharge theUPS batteries, then convert to 110V again when needed, and convert back to 12V to run lights, etc.).

One option (when stationary) would be to put the UPS between the generator and the 110 feed for the RV. When the generator is off, the 110V from the UPS would recharge the battery if necessary, and when the generator runs, it would feed the RV and at the same time recharge the UPS.

Wonder what other people have done ...

 

[Dona40]

Lots of battery and lots of solar. Battery's run down faster than you would think and charging is measured in hours not minutes.
go big or go home. I have 8 6 volt battery's and 750 watts of solar with a 50 amp charge controller and is still not enough. Of course I'm married to a power hog. Gota have the luxuries right.

 

[bherron1]

Same problem, furnace fan is the power hog. Best solution, catalytic heater with no fan. Thats my next project. Been running a little honda 2200 on eco mode very quite, to charge batteries and it takes 6 to 8 hours to full charge each day. I fill it up bout 3pm and it shuts down out of gas bout 9pm Every thing else will run for days off my one battery. Fridge is LP, stove is LP, lights are LED. Water pump dont run much. Little honda even runs the AC on eco mode with a easy start. Amazing ! We prefer to boon dock at all cost.

 

[Dona40]

Same problem, furnace fan is the power hog. Best solution, catalytic heater with no fan. Thats my next project. Been running a little honda 2200 on eco mode very quite, to charge batteries and it takes 6 to 8 hours to full charge each day. I fill it up bout 3pm and it shuts down out of gas bout 9pm Every thing else will run for days off my one battery. Fridge is LP, stove is LP, lights are LED. Water pump dont run much. Little honda even runs the AC on eco mode with a easy start. Amazing ! We prefer to boon dock at all cost.

We bought one of those cat. heaters (probably too big) and piped a quick connect in to the living room. Keeps the place toasty and we don't have to run the aqua-hot except for showers. As of now, propane is cheaper than diesel and it's direct heat. The real test will be in January at the Central Oregon camp.

 

[AbdRahim]

I have six 6v AGMs and I don’t run anything but lights and fans on batteries alone. I always need to run the generator to provide electric heat, furnace heat, or A/C. Dona40 has the correct answers.

 

[Bob K4TAX]

To conserve energy, change all lamps and bulbs to LED types. They require only 10% of the energy of an incandescent. I run 10 LED's for one hour and consume the same energy as 1 incandescent for 1 hour. As to 100Ah batteries, a 50% discharge is about the safe limit without battery damage. At a 20 amp charge rate, the efficiency of the charge is only about ~60 %. This is then 12 amps of effective charge to a 100 Ah battery at 50% or 50 Ah. The charge time would be about 4.2 hrs.
Be sure to reduce the furnace temperature starting at bedtime to reduce the run time. Yes, those furnace blowers are energy hogs. Add a blanket or two to the bed. And yes those radiant propane heaters, even the ones that run on a 1 lb. bottle are really nice. {Also with an adapter purchased from Tractor Supply and other like places, one can refill those 1 lb bottles off of their main propane supply.}
Also if you have or use a DC to AC Inverter for TV's and the like, they are energy hogs as well.
Forget the idea of a UPS except for the purpose they were intended. The typical run time for a UPS, depending on load, is usually less than 1 hour unless it has BIG batteries.
If all of this is a concern, then add a 2nd 100 AH battery and a battery selector switch. But I advise to use Battery A or Battery B and switch as necessary. Do not use the BOTH position or you'll have two flat batteries. Reason: the lower voltage battery will discharge the higher voltage battery. This is based on the internal resistance of each battery. It is OK to select BOTH for charging purposes but not for running purposes.
Energy management is the key to all of this.

 

[GypsyR]

A UPS is just 12 volt (usually) batteries in a box with an inverter and an extra circuit board. Batteries you already have, but it sounds like you could use some more. That would probably be my first move.
Then keeping them charged. Much as I love the idea of solar, it just doesn't make sense for how we use our coach. I don't really even use the batteries much though I have backyard camped to see what I had and how long they went. For me a small portable and quiet generator would be the most practical way to fill the gap. So far I've been able to just use the main generator. If I were to really think I was going to boondock enough to buy that little generator I would also invest in at least one soft start kit for one of the roof AC's too. Now that I've written that and sit here looking at it, I think I will do just that. Pretty sure I can come up with camping scenario to use the extra equipment.

 

[sanda]

I also like to boondock and use my generator. I have found that hooking up a conventional battery charger directly to the batteries will charge them a lot faster than running the power through the converter.