Rv battery/inverter question

[BrianF]

So my plan is to do a bit of upgrading to our 6 horse Trailswest. Its a basic weekender and currently has a single group 24 RV battery to power the lights, inside and out.

It has a dual battery box, which looks to have room for maybe dual group 27s. Regardless I will upgrade to dual batteries but want to add an inverter and solar charger.

The end goal is to power a couple fans, charge some cell phones and maybe run a small tv. Realistically it would be used in an 8 to 9 hour window during night. Eventually we may install a small air-conditioner but likely only used when we have power hook up.

Right now looking at a 1500w inverter but wondering if thats an adequate size or if one should go bigger with 2000w? I'm most certainly not smart with electrical so any advice is greatly welcome.

 

[ctechbob]

So my plan is to do a bit of upgrading to our 6 horse Trailswest. Its a basic weekender and currently has a single group 24 RV battery to power the lights, inside and out.

It has a dual battery box, which looks to have room for maybe dual group 27s. Regardless I will upgrade to dual batteries but want to add an inverter and solar charger.

The end goal is to power a couple fans, charge some cell phones and maybe run a small tv. Realistically it would be used in an 8 to 9 hour window during night. Eventually we may install a small air-conditioner but likely only used when we have power hook up.

Right now looking at a 1500w inverter but wondering if thats an adequate size or if one should go bigger with 2000w? I'm most certainly not smart with electrical so any advice is greatly welcome.

I would go bigger, and if the funds are there, true sine wave.

Either way, the AC/Fans are going to be the biggest draw out of that list (not so much the fan) as compressor startup draw will pull quite a bit until it is running. You'd have to do the math as far as current draw overnight and if the batteries would support it. Running a fan won't be too bad, but AC is another story. Either way, I'd find the most efficient inverter and AC that you can. Every bit of power consumption will help.

Personally, if you have the skills, I would skip window/RV units all together and retrofit a mini-split heat pump to the coach. It will be way more efficient than most all window/RV units, but will present some hurdles to jump as far as mounting/plumbing/etc.

Good news is that Lithium batteries are coming down in price and they pack quite the punch. That's where I would start for your storage needs.

 

[LazyDog]

The DIY HVAC Guy, check his videos off-grid. I try to attach video link but it said not available.

The latest video is on a mini split that can run of solar. I am actually looking at buying something similar to my mom's house in Mexico. The heat is been brutal this year.

 

[eljefino]

Batteries and an air conditioner are basically incompatible. Like you wrote, only run the AC when plugged into shore power. I had an RV with roof AC, 12k BTU IIRC, and the 4kw Onan genset was sized for it. Running AC off your lead acid batteries will deplete them in 30 minutes to an hour, not be good for the batteries at all, and you'd be towing hundreds of pounds of batteries that you'd have to replace every five years if you want to make this work.

Use a generator or shore power for the AC.

As for your solar dreams, they're great, it's easy to do what you want to do, the timing has never been better. I have an off grid cabin with 20 year old tech that still works amazingly well.

"True sine wave" is a marketing term, inverters create an analog copy of a digital signal just like a CD does of a sound recording. They can get close, read the fine print, or find tests somewhere. A better brand name vs something from Alibaba will probably make you happier.

 

[Dave Sherman]

"True sine wave" is a marketing term, inverters create an analog copy of a digital signal just like a CD does of a sound recording.

Some cheap inverters put out a stepped square wave that doesn't look anything like a sine wave. That might work for an incandescent light bulb, but motors and transformers won't like it. Better inverters labeled "true sine wave" actually generate a sine wave that will work much better with motors and transformers, even if there may be some high frequency noise.

 

[fsdork]

Some cheap inverters put out a stepped square wave that doesn't look anything like a sine wave. That might work for an incandescent light bulb, but motors and transformers won't like it. Better inverters labeled "true sine wave" actually generate a sine wave that will work much better with motors and transformers, even if there may be some high frequency noise.

I think @eljefino 's point (at least in part) is that the degree to which a questionable "pure sine" inverter smooths out the steps in the wave may not be as clean as one might think.

As to the OP's question about sizing, consider what your realistic loads will be vs. duration. I have a 1000W pure sine inverter in my travel trailer. The vast majority of the time it is powered up, it's running a cell phone charger, which means it is way over-sized and is wasting a lot of energy from the batteries. Before our next trip, I'll be installing a 12V to 5V step-down converter with USB outputs so I don't have to run the inverter for charging phones and tablets. If you're running the inverter to watch TV anyhow and top up the phones while you're at it, that's fine.

Each electrical device should be labelled with its max current draw. By adding the max input (amps) of each device you plan to use simultaneously, and entering that number in the Current field of the calculator linked below - using the 110V default in the voltage field - you can run the calculation and determine the total watts required to run those loads. Give yourself a bit of headroom - say 25%ish.

https://www.calculator.net/ohms-law-calculator.html

Also keep in mind that the inverter isn't the only limiting factor when it comes to max output. The max output rate of the battery, coupled with its size - and the wiring used in the system - will determine how much the battery can provide to the inverter in the first place. Dual group 27s would get you in the ballpark of being able to support 2000W of output - the single group 24 puts you closer to ~800W. 2000W out from an inverter means more than 2000W pulled from the batteries, as the conversion isn't free. Just how much more will be determined by the efficiency of the inverter.

As others have said, forget AC on an inverter and batteries. There are systems out there which can do it, but we're talking a whole other world of large lithium battery banks and expensive components.

 

[BrianF]

Gentlemen, thank you!! You armed me with quite a bit of information.

While I figured air conditioning would ve far fetched off battery, we realistically figured we would run it either off plug in or small gen set. We dont boondock as the horse shows we go to are held at big show grounds, usually with power campsites or we hotel it.

I began grabbing wattage from the suspected appliances and will tally it up.

I did a quick measure of the battery box and twin group 27s will not fit, close but not enough. I am not tearing the factory steel box off to relocate or install bigger.

 

[PandaBear]

I have no RV experience but I would imagine you need to worry more about the startup current draw of the AC and size your inverter appropriately. You either have to do that or you have to downsize your AC to the inverter size you can accept, and have to tolerate it taking time to heat and cool your system. If you can get a unit that would slow start it would help your inverter demand as well.

The technology is there but not sure if products are available for RV market. Basically this is what a hybrid and EV AC is about and they don't surge on/off but they gradually increase and reduce compressor load like a variable AC in residential one.

 

[UncleDave]

I've installed dozens of Inverters building dog grooming vans, trailer and Rv's

For guys with budget the Outback FX series with the built in charger, Xfer switch, and floating neutral is a phenomenal unit when going back and forth between genset home and battery power.

For building it piecemeal I like and have had good luck with AIMS, Victron and Samlex.
It's easy to remember with a 12V source everything is 10X at the batteries.

Sounds like the OP isn't going to have a lot of battery capacity.

 

[BrianF]

So I had originally looked at this cheaper 1500w inverter. Looking at the specs now, it reads: "modified sine wave output."

A more expensive unit, same output states: "pure sinewave."

I agree that I will battery output as a major limiting factor, regardless of inverter capacity. I will have to work within those confines.

 

[BrianF]

So my next question, should one stick with two 12v batteries or wire up two 6s?

 

[BrianF]

So I snagged a 100w solar charger, a 1500w true sine wave inverter and a little 2000w genset. Measured my battery box and no dice on dual Group 27 batteries, its just a hair under sized. So I'll find something that fits.

The little genset, which I got for cheap from a buddy, which was unplanned, changes things. It will power whatever little items we need during the day or evening and at night, the batteries can run a couple small fans and charge some electronics.

 

[eljefino]

Look into 12VDC fans, that way you won't have losses with the inverter "idling."

 

[JimPghPA]

About 2 years ago I bought a very high quality 2200 Watt inverter that is made by Mean Well.

This is a big step up in relialibality from most inverters out there that may or may not work, and may or may not provide a clean sine-wave that can run anything. Some electronics and electrical items may not work if powered by an inverter that does not have a very clean sine wave. Some items can even be irreversible damaged.

Mean Well inverters make as clean as or even cleaner, sine-wave as you will get from a utility company. These are inverters that are used in expensive yacht, these are very clean sine-wave output inverters. And their reliability is medical grade.

The down-side is that they ain't cheap. Aug 1, 2022 I paid 814.03 + 15.19 shipping, + 58.05 tax = total of 887.27 for one.


Keep in mind that all inverters have the maximum power they can produce derated as the ambient temperature increases. So that alone is a good reason to buy something with extra capacity.

Here is an example of the derating for my Mean Well NTS - 2200:

-13F to 104F 2200W
122F 1760W
140F 1100W
158F 800W

input voltage
10vdc 1760 W ramps up to 2200 W @ 10.5 vdc
10.5 to 16.5 vdc 2200 W

these Mean Well inverters have a lot of built in protection to prevent accidental damage.


Generally inverters are designed to hand only one of several input voltages.

12VDC, 24VDC, 48VDC

My 2200 W 12vdc in is wired with 0 GA. Stranded pure copper for the 12 vdc input. And that ain't cheap.

I had a vehicle stereo shop do the 0 GA. wiring. They had the wire and hydraulic crimper. I had bought a 350 A / 185 A at idle alternator from APEX, and I put in a larger battery. On youtube look up "the big 3 upgrade". Wire to the back seat for the inverter, quick connect, fuse, better battery connections, install and wire the upgrade alternator, cost me $1,000.00 at the stereo shop. Copper is expensive, and that is why people use 24vdc or 48 vdc when they can because they can use thinner less expensive copper wire.

Avoid like the plague aluminum and aluminum with copper clad wire.

Mean Well makes them in 300 W, 450 W, 750 W, 1200 W, 1700 W, 2200 W, 3200 W

and they make them in 12, 24, 48 vdc in

the output is adjustable by user to any one of 100, 110, 115, 120 vac

They also make 200, 220, 230, 240 vac units

And they make units that can be used as a ups but that is an additional design and more expensive.

they also make some battery chargers, maintainers, and other supplies

Higher voltages allow you to use thinner less expensive wire. But the dangers of death from electric shock increase as voltage increases.

These are very high quality inverters and very reliable, and just about impossible to accidently electrically damage. And very expexsive.

You pays your money, and you makes your choice.

BTW, the one I got has two fans that it automatically varies the speed of to minimize power used, but maintain proper cooling when required.


Sometimes it better to cry once in the beginning about the price, and know you have something that is rock solid medical grade reliable, than put up with the hassle of something that breaks when you need it leaving you something that does not work and has to be thrown away, and you having to buy something better later.

What ever you get, be sure it has plenty of cooling ventilation and keep the air filters clean. Heat and dirt kill even good equipment.

When I bought mine, I had to call Mean Well and find out from them which of their electrical distributors has the one I wanted in stock. I bought from Mouser.

 

[JimPghPA]

One of my brothers bought a cheap inverter because his Wife wanted to be able to use an electric blanket when they were traveling in his truck in the winter. The output was not a clean sine-wave and the controller for the electric blanket went up in smoke. Some things do not like the stepped dirty sine wave that cheap inverters put out.

 

[JimPghPA]

BTW, the -13f in the derate speck is probably the lowest temp it should be exposed to. Probably would freeze and damage capacitors in it at temps lower than -13f.

----------------------------------

And the Mean Well inverters can handle a lot of surge (like twice the rated power) for a very brief time like when starting an AC compressors. Of course the DC supplying it, has to have enough capacity to handle that surge.

 

[BrianF]

Thank you again for you input everyone. Its always appreciated!

I think I will keep the simple DC wiring for the lights and look at that DC fan so I can keep a few items bypassed from the inverter, I much like that idea.

Thankfully we will not be using the trailer in the winter so no worries on whether components will work or not.

 

[JimPghPA]

Digitai-Key sells some decently large low voltage DC fans. Usually they are used to cool computers. In general larger fans WITH LOWER RPM's are the quiet ones.

Boating supply stores may be a good source for 12 volt led lights. Of course you want to stay with led's because they consume a heck of a lot less from the battery so the battery will last much longer between charges.

Probably the best led's are made and sold by VLED's. These are high quality that last extremely long because they have built in heat-sinks that most of the other cheaper led's do not have.

 

[JimPghPA]

Group 27 deep cycle batteries in good condition have an Amper-hour capacity of 85 to 105 Amp hours. And of course there are expensive lithium, or lower cost lead acid. Lead acid in general do can have their life shortened by very deep discharged. A better name for these wold be higher amper hour lower CCA batteries. If you deep discharge them often you shorten their life. So it is best to not discharge them below 50%. You can discharge more than that but it is not good for their life expectancy.

So let's be generous and do some math here.

2 group 27 at 105 amper hours capacity each, providing 12 vdc = 2 X 105 X 12 X 0.75 (assume a discharge leaving only 25% left) = 1890 Watt hours. Now assuming you do not want to destroy the batteries by over heating them by discharging them too fast, let's limit the discharge rate to 3 hours.

1890 / 3 = 680 watts from the batteries, continously for 3 hours.


Assume an inverter efficency of 94%

680 X 0.94 = 638.2 Watts

So, with 2 good charged group 27 batteries rated at 105 amper hours, you might be able to provide 630 Watts for 3 hours. Or with less of an electric load such as 315 Watts for 6 hours.


The above is just approximately what you can expect. If the amper hours of the batteries was lower or higher then you could expect less or more Watt hour capacity per discharge.