Off grid RV decisions

[Capt Dale]

We are taking possession of our Outdoor RV 250RKST in mid-summer and are deciding how large of battery bank and inverter to purchase. We will have 340w of solar electric with space to add more. We are going to go with at least two of the Battleborn Lithium 12v 100ahr (for weight and have room for a total of four). We also will have the Hutch Mountain Air Easy Start 364 for the a/c with a Honda I2200 generator.

My question for those who have off-grid electric is what size of inverter and battery bank is normal to run entire RV minus the a/c system? I know it’s all in a formula but we do not have it yet and I am thinking a 3000w pure sine inverter with a battery bank of 400ahr lithium batteries...

[lanztek]

This guy did some great testing right at the Battle Born factory. Very interesting to see all types of batteries side by side:

https://www.youtube.com/watch?v=iy3hga_P5YY

[jcussen]

Originally Posted by Capt Dale

We are taking possession of our Outdoor RV 250RKST in mid-summer and are deciding how large of battery bank and inverter to purchase. We will have 340w of solar electric with space to add more. We are going to go with at least two of the Battleborn Lithium 12v 100ahr (for weight and have room for a total of four). We also will have the Hutch Mountain Air Easy Start 364 for the a/c with a Honda I2200 generator.

My question for those who have off-grid electric is what size of inverter and battery bank is normal to run entire RV minus the a/c system? I know it’s all in a formula but we do not have it yet and I am thinking a 3000w pure sine inverter with a battery bank of 400ahr lithium batteries...

3000 watt inverter, and 4 battleborn's should be fine if you have a propane fridge. I have 6 battleborn's and rarely go below 85% SOC in the morning before solar starts to recharge the batteries.
Best to get a good shunt style battery monitor. Victron makes excellent 3000 watt hybrid inverters and solar controllers and battery monitors. With a soft start, hybrid inverter and the Honda 2200, you should have no problem running ac off generator when necessary.

[RVPioneer]

There is no normal. Every RV will have different needs.

To minimize or eliminate generator run time, it will be necessary to determine your average daily power consumption and install sufficient battery capacity to meet those needs. Then a large enough solar array will be required to restore that energy.

[Capt Dale]

That’s an after the fact thing, I’m being pre-active.

[Capt Dale]

Good in put, thank you.

[R.Wold]

Originally Posted by jcussen

3000 watt inverter, and 4 battleborn's should be fine if you have a propane fridge. I have 6 battleborn's and rarely go below 85% SOC in the morning before solar starts to recharge the batteries.
Best to get a good shunt style battery monitor. Victron makes excellent 3000 watt hybrid inverters and solar controllers and battery monitors. With a soft start, hybrid inverter and the Honda 2200, you should have no problem running ac off generator when necessary.

My thoughts exactly You can also easily get by with four batteries (or less with a propane fridge) as long as you are fully charged when you run out of sun.
I run a 15k btu AC off my Victron 24/3000 without an easy start, but have more solar and battery capacity. So a 3kw inverter will do the job.

[RVPioneer]

Best of luck.

[Persistent]

Capt Dale,

The above posts are good advice. I agree 4 Battle Born 100 amp hour batteries will work well with a 3000 watt inverter. You can't go wrong with that combination. I agree you need to calculate an energy budget because the limited power generated by the solar array and weather conditions will matter. A high quality 2000 watt generator or a 3000 watt cheap one may be necessary depending on all the details. Certainly 24 hour air conditioning will require the generator.

The U-tube video is interesting. At minimum you can probably see that optimizing battery power is amazingly complected.

You said you will have an Outdoor RV 250RKST. The test plans in the video apply mainly to high occupancy big motor coach systems. If you are planning high occupancy and high power appliances for your Outdoor RV 250RKST, the conclusion to use lithium is valid for both cost and performance.

You can optimize installation by installing the lithium in heated space. Possibly inside the cabin where they will be heated whenever the unit is occupied. Using the heated version of the BB's is great, but the power lost to self heating in an outside storage space is wasteful of scarce battery and solar performance.

I think the video analysis is pretty good, however, one major error favors the lithium. The test uses what he says is the lead acid battery manufacturers specification of 12.2 volts as the 50% cut off. It is not true.

The 12.2 is using the static voltage profile, not the discharge profile. He later determines in a complected way the the actual 50% discharge level is closer to 11.8 volts. Of course that changes with the discharge current. The higher the discharge rate, the lower the cut off to achieve 50% discharge. Static 12.2 volts must be measured after 4 hours of neither charging nor discharging. He did not do that.

The result is cost of power for the lead acid batteries is over stated. Calculated cost for life time of the lead acid batteries will also be overstated because you will get more cycles in the life because the batteries get more cycles with less than 50% discharge. The tests all cut off lead acid discharge before reaching 50% discharge so more cycles will be available.

Temperature compensation for both charging and discharging is required for both lithium and lead acid to get accurate results and maximum performance. Most RV's do not use temperature compensation. Many expensive motor coach energy management systems do. So this may or may not effect your decisions.

That is why I recommend both AGM and Lithiums be located in heated and cooled indoor spaces. Not in open bays as are most motor coaches. Flooded cell batteries must be located in open bays.

The cost of open temperature compensation in open bays should have been added to flooded cell costs. Also the cost of maintenance including acid damage from charging flooded cells should have been added to flooded cell life analysis.

I wish you good luck and happy trails ahead!

[SV K]

You should be able to approximate your daily usage without an audit by defining your intended uses, TV, coffee maker, lights, stereo, fridge, microwave, etc.…hours of use times each items amps draw. You can find those draws online. The result will give you a rough enough number to size your system.

The other variant will be how you would like to charge the system. Do you want to lessen generator use in the re-charging process? If you plan on solar being the main charging vehicle do you camp in the sun or under the trees?

Lots of variables to consider or…just start off with your original plan, but design in such a way that will allow you to add more battery and/or more solar as you see the need.

You already have the ability to add battery capacity planned, and a 3000watt inverter should meet any future needs so you’re good there. If you have roof space for more solar, but don’t want to add it now, maybe layout the current panels in such a way as to allow the addition of more panels later. You can also add another solar charge controller at a later time or buy a controller now that has the capacity to handle the additional panels.

I'd feel remiss if I didn't mention you could save some bank and end up with a pretty powerful battery if you are willing to put it together yourself. Just a thought and no disrespect intended toward Battle Born.

[twinboat]

Pickup a Kill A Watt meter and plug each electric item in it and record the data.

A 8 to 10 cubic foot, resedental refrigerator, is going to use 80 to 100 AH a 24 hour period. That's with no solar.
With solar, its not going to use any energy for 6 to 7 hours, as long as the sun is shining. So now your only using 60 to 75 AH a day, not so bad.

Size your battery bank to use at least 60% to 70 % of it. If your only using 25%, you have too many batteries.

[Rumline]

Originally Posted by Persistent

I think the video analysis is pretty good, however, one major error favors the lithium. The test uses what he says is the lead acid battery manufacturers specification of 12.2 volts as the 50% cut off. It is not true.

The 12.2 is using the static voltage profile, not the discharge profile. He later determines in a complected way the the actual 50% discharge level is closer to 11.8 volts. Of course that changes with the discharge current. The higher the discharge rate, the lower the cut off to achieve 50% discharge. Static 12.2 volts must be measured after 4 hours of neither charging nor discharging. He did not do that.

This right here! The rest of the post is great too but I didn't want to requote it all.

I disagree with the 400Ah lithium bank and 3kw inverter recommendations. Sure, having that would be awesome, but OP's question was how much is normal to "run entire RV minus the a/c system." Since OP's trailer has a propane fridge, I think 200Ah lithium and 2kw inverter would be fine, saving ~$2500. Source: I used to have a 23 foot trailer with 340w solar, 400Ah AGM, and no generator. We boondocked extensively and we never ran out of power even when camping in freezing temps and running the furnace all night.

[JHinman]

I have a new Outdoors RV also (24KRS), and have two Battleborne 100AH batteries under the bed. For the kind of boondock camping we do that is plenty of battery. In the summer, one Battleborne is probably plenty. I charge with my Honda 2000i. I have one of the Zamp 170 watt solar panels, but it does not produce much at all.

My trailer has a large battery tray on the tongue, which should hold four batteries. I chose not to put them outside, and I suggest you consider putting your inside also. If your bed is like mine there is space between the under-bed drawers that can be used. The batteries are out of the way, are warm, and you don’t lose any storage space.

There is not a lot of room there. You might want to look at other battery brands to see if their shapes would let you fit more capacity in that same place. I used Battleborne because I already had one of the batteries.

The space is close to the “junction box” under the trailer, so the battery installation is pretty easy. I do not know yet what it will take to install a hybrid inverter, but I will find out. I will probably buy one in the next couple of weeks.

I have read on this forum that a 2000 watt inverter is sufficient for the microwave and small kitchen appliances. Since a toaster and a microwave draw 900 or 1000 watts each that should be good as long as I don’t run them at the same time.

Both Victron and Renogy recommend battery banks of 350 AH or more for their inverters. I am still wrapping my head around that - it seems that my two Battleborne batteries will provide enough current for a 2000 watt inverter. They may provide enough to run a 3000 watt inverter, although it may not actually output a full 3000 watts.

I have been posting questions on this forum on this subject. Once I get an inverter in operation I will post results. Don’t hold your breath, though, as I work very slowly.

[SV K]

I don’t understand the need for the recommended 350ah to run a 2000w inverter if you are using Lifepo4 other than 1) the “Battery’s” BMS is not designed and/or won’t allow it or 2). The voltage drop caused by the high amperage draw of a powerful device might trip a low voltage cut-off on the inverter.

Certainly the Lifepo4 cells that make up a “battery” can handle the discharge. I think Will Prowse on Youtube hooked up a hair blow dryer to several different 100ah po4 packs to test their capabilities and they worked fine.

I’d contact the MFR’s and look for definition of the recommendation. If you are looking at Victron you could join their online forum and pose the question to dedicated users.

Personally I wouldn’t hesitate to make coffee, toast or micro a pot pie on 200ah Lifepo4, but I am interested in what you learn.