Building Battery Bank and All That Comes With It

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
Z

Zoomwalt

Member
Joined
Aug 5, 2021
Posts
6
Location
North Carolina
Hello,
Not only is this my first post here, but as far as I can remember this is my first post on a forum ever as I usually pop in and pop out when doing research.

I have a 2008 Four Winds 5000 28A Class C that I am in the (early) process of outfitting with a good battery bank, inverter, etc for boondocking. I have a pretty solid plan of how I will proceed and in all honesty, it will probably be a multi phase situation as I will be using the camper weekly regardless of if the full install is finished or not. Heres the plan so far:

To start, I'm planning on picking up a 200ah agm battery and 2000w inverter as the backbone of the system. Prior to the full install, I'm ok with using the inverter to shore power cable method combined with a small 100w portable solar panel as these weekly trips are typically going to be one night only for now. Needless to say, I'm aware that the converter/charger would need to be manually turned off. For this phase, I was planning on using the outdoor storage compartment on the front passenger side for ease of access and plenty of space.

My plan for full install would be to hide the battery and inverter in the front facing dinette bench along with a second transfer switch with a built in relay for the converter/charger. The existing power systems are in the opposite bench with routing already in place between the two so making the jump between the benches should be pretty easy. This routing will also assist with the eventual permanent solar install.

The one thing I've not gotten much info on is if all of this expansion can still safely be run in series with the existing, alternator charged, coach battery set up. Im aware that the existing flooded battery would be a no go, but beyond that, am I safe to just hook that alternator charged cabling up to whatever battery bank I have and roll with it? Does running solar to that same system matter if its also connected to the alternator? What would happen if the alternator and solar charge controller were both feeding those batteries simultaneously? Just a really fast recharge?

Holy crap that was a lot. Sorry for the mouth full but any input would be appreciated.
Thanks!
 
Missing from your post is your expectation of performance. A 200Ah AGM colocated with a 2kW inverter will work, depending on your definition of "work". That definition would be comprised of duration of operation, power delivered and any recharge recovery time. The FLA's will contribute their share but not knowing their cabling, capacity or merit it's an unknown.

For charging from an alternator you're OK, because it's not supplying power long enough to worry too much about critical absorption and float charge setpoints. That's more for the converter/solar controller which typically supplies full charge cycles. Alternators aren't that great at charging storage batteries in general but both AGM and FLA will bulk charge equally well.

Solar is another discussion altogether. 100W is a warm fuzzy and something to get started with but at least in my experience isn't much more than a maintenance charge for a class C size house battery bank. For one day trips I'm not sure it's enough power to bother setting it up, you'll be packing up and leaving before it does much good. It can be connected along with your alternator and/or converter and the way it works is it will contribute an amount of power commensurate with the terminal voltage the solar controller sees on the batteries. Since the panel output is small in comparison to the output of an alternator or converter, it's contribution will be small.

Mark B.
Albuquerque, NM
 
Thanks Mark!
My definition of work would be assuring that 1-3 fans could be run throughout the night and that a TV could be used for a few hours daily. Both of these items are mostly for my 3 small children then would be along for the ride. Fridge would be on propane, wouldn't use the microwave at all, and all lights are LEDs but still wouldn't be using them much if at all. I still plan to install at least 200w-300w of solar permanently.

So to the permanent setup topic:

I could either route the existing cables coming from the alternator straight up into the dinette bench to the larger battery thus leaving the battery storage area under the rv empty OR I could add a new 100ah agm battery there as well and wire it in series with the 200ah in the dinette bench. Seems like if I go ahead and do it that way, I would avoid having to undo work if I want to expand the bank later.
 
A few observations. You don't need a 2kW inverter to run a TV and a few fans. The issue with that is the larger the inverter, the higher it's idle current and wasted power when running small loads especially over a long period like overnight. I have a 300W inverter and it runs my TV's easily, less than 100W. I wouldn't run AC fans, get some 12V ones and then the issue of the inverter efficiency disappears entirely. RV LED lights are typically 12V as well, so you wouldn't need an inverter for those. Running a 2kW inverter implies large loads like microwaves and hair dryers which is certainly done but is an entirely different operating dynamic.

I'm kind of confused about your battery bank aspirations. Might be useful to say what you have or what you'd like the final bank to look like. Series connections implies 6V batteries but if you're adding capacity that's going to be done in parallel. Also for long term performance and longevity the batteries should be the same type, size and age or over time they'll degrade faster than if they're not matched. Maybe it's a don't care for your goals, just putting that out there. The alternator connection is determined same as the primary connection to your house, determined by the physical layout of the batteries. So figure out the battery layout, and the cabling configuration goes from there.

Mark B.
Albuquerque, NM
 
The first big question that comes to my mind, is why not make the jump to Lithium batteries, this is 2021, and while it is true lithium needs some special support equipment, DC-DC chargers, etc. those items are getting cheaper all the time, and once you consider lithiums longer service life, it not only outperforms AGM, but is also cheaper in the long run.
 
And just to present the counterpoint to lithium, incorporating it requires a refit of the charging equipment which adds cost and labor. In order to make total cost of ownership less expensive than lead, one has to use up all the delivered Ah those batteries provide which translates to very frequent use. So unless you're cycling your batteries nearly every day, year after year your cost for delivered Ah for lithium will likely be higher vs lead. Some consider their other performance attributes to be worth that higher cost and that's fine, but lithium isn't more cost effective by default.

Mark B.
Albuquerque, NM
 
Mark, I am not so sure about that Lithium is getting cheaper every month, and AGM is staying the same or going up. It has been about 6 months since I last ran the numbers, and at that point things were starting to get close.
 
FWIW I see a lot of these threads with a couple of batteries and a 2000W inverter. Way too much inverter or way too little battery.

The key to a DC to AC system is a balanced system that considers storage, power draw X time and replenishment in a balanced system.

Marks observations are spot on. I run a 400W inverter and it powers the TV and my cell booster antenna, the fridge and gas water heater controllers and laptop/phone chargers if needed.

I have no aspirations to run any AC appliances in my RV.

Another great tip from Mark was to add DC fans. I have replaced all the incandescent bulbs with LED fixtures and have permanently installed DC surface mount fans in all areas.

I have 200 a/h of battery and with casual observation I reckon they would run a couple days with my "normal" load which would include the fridge & water heater controllers running them on on LP gas.

If that doesn't work then I have the iron lady in the back who makes AC power at the touch of a button.
 
Mark,

Your confusion is warranted as I mistakenly said series instead of parallel when referring to the multiple battery situation.

Currently there is an older flooded battery as the coach battery and regardless of whether I upgrade the whole system, it needs to be replaced. I suppose I could start there and see what kind of performance I get with a new 100ah agm in there.

Long term, I would like a system that is robust enough for several days of boondocking with again, mostly just fans and a TV. Through the inverter though, I could run fan only on my ac unit.

Lithium batteries are definately intriguing but I will continue to watch the prices go down before I make that investment for myself.
 
Ex-Calif said:
FWIW I see a lot of these threads with a couple of batteries and a 2000W inverter. Way too much inverter or way too little battery.

The key to a DC to AC system is a balanced system that considers storage, power draw X time and replenishment in a balanced system.

Marks observations are spot on. I run a 400W inverter and it powers the TV and my cell booster antenna, the fridge and gas water heater controllers and laptop/phone chargers if needed.

I have no aspirations to run any AC appliances in my RV.

Another great tip from Mark was to add DC fans. I have replaced all the incandescent bulbs with LED fixtures and have permanently installed DC surface mount fans in all areas.

I have 200 a/h of battery and with casual observation I reckon they would run a couple days with my "normal" load which would include the fridge & water heater controllers running them on on LP gas.

If that doesn't work then I have the iron lady in the back who makes AC power at the touch of a button.
Click to expand...
Thanks for input.
What was your method of powering those fans throughout? Did you run individual, dedicated 12v runs to power them or did you have enough existing 12v terminals that you just used those? My 2008 only has one on the dinette so I would have to add some but I wouldn't think that would be too difficult.
 
Fans draw but a few watts so running some light gauge zip wire a few places would do the trick. I'm not sure I'd bother hiding that in walls or behind cabinets, that something you can just route out of the way maybe tuck into the edge of carpeting or moulding.

As a data point I can go about 3 days doing everything I want to do in my class A with 200Ah GC2's. Pump, lights, TV, charging stuff, whatever. With a few hundred watts of solar on top of that you may end up net zero or at least extend your operating time to a point where your trip is up before your batteries are empty. Since you don't have any hard numbers on usage yet it's hard to predict but my take on it would be a minimum of 200Ah plus your panel(s), run it for a few trips and see how it goes. If you don't already, you should have a battery monitor to be able to know the state of your batteries at any given time.

I get that on paper you can easily make a case for lithium vs lead acid but that's only if you use them completely up before they expire. Some people might and then it's a slam dunk. I would guess that most RV'ers come nowhere close to using up the service life of their batteries just camping on weekends and maybe a few weeks a year. So just making the point that the application is going to be a part of the TCO formula. When I run the numbers for my use it amounts to spending more than a grand for a setup that I would realize no operating benefit from, so it's a non starter for me. As lithium becomes cheaper that gap closes but it's not close enough for my application yet.

Mark B.
Albuquerque, NM
 
I think Mark's advice is right on target for what you are trying to do. Especially as an initial effort. More battery, less inverter, and some simple 12v wiring. Maybe an auxiliary plug-in charger for when you have external power (depends on what the coach has for converter). Start with 1-2 12v AGMs, whatever the budget can handle, abd build up.
 
Zoomwalt said:
Thanks for input.
What was your method of powering those fans throughout? Did you run individual, dedicated 12v runs to power them or did you have enough existing 12v terminals that you just used those? My 2008 only has one on the dinette so I would have to add some but I wouldn't think that would be too difficult.
Click to expand...
I primarily tapped into existing lighting wiring. The light wiring was sized for 40W incandescent (~3amps) and the LED replacements draw practically nothing so parelleling close to the light fixtures is no problem. The fans probably draw less than 1/2 amp.

In my RV it was a simple matter to pry up the "floors" of the overhead lockers to expose the existing 12V circuits. The only place I had to run a set of wires was overhead the driver's station and for that I ran them behind the window edge molding and into the cabinet. Basically following the path for the speaker and dome light wiring.
 
Mark_K5LXP said:
Fans draw but a few watts so running some light gauge zip wire a few places would do the trick. I'm not sure I'd bother hiding that in walls or behind cabinets, that something you can just route out of the way maybe tuck into the edge of carpeting or moulding.

As a data point I can go about 3 days doing everything I want to do in my class A with 200Ah GC2's. Pump, lights, TV, charging stuff, whatever. With a few hundred watts of solar on top of that you may end up net zero or at least extend your operating time to a point where your trip is up before your batteries are empty. Since you don't have any hard numbers on usage yet it's hard to predict but my take on it would be a minimum of 200Ah plus your panel(s), run it for a few trips and see how it goes. If you don't already, you should have a battery monitor to be able to know the state of your batteries at any given time.

I get that on paper you can easily make a case for lithium vs lead acid but that's only if you use them completely up before they expire. Some people might and then it's a slam dunk. I would guess that most RV'ers come nowhere close to using up the service life of their batteries just camping on weekends and maybe a few weeks a year. So just making the point that the application is going to be a part of the TCO formula. When I run the numbers for my use it amounts to spending more than a grand for a setup that I would realize no operating benefit from, so it's a non starter for me. As lithium becomes cheaper that gap closes but it's not close enough for my application yet.

Mark B.
Albuquerque, NM
Click to expand...
This all sounds great, Mark. I do have the factory installed battery monitor, but its garbage. Just leds, no actual percentages so something more substantial was already on my list.
Ex-Calif said:
I primarily tapped into existing lighting wiring. The light wiring was sized for 40W incandescent (~3amps) and the LED replacements draw practically nothing so parelleling close to the light fixtures is no problem. The fans probably draw less than 1/2 amp.

In my RV it was a simple matter to pry up the "floors" of the overhead lockers to expose the existing 12V circuits. The only place I had to run a set of wires was overhead the driver's station and for that I ran them behind the window edge molding and into the cabinet. Basically following the path for the speaker and dome light wiring.
Click to expand...
Right on. Which fans did you end up using? Do you have any pictures?
 
Gary RV_Wizard said:
I think Mark's advice is right on target for what you are trying to do. Especially as an initial effort. More battery, less inverter, and some simple 12v wiring. Maybe an auxiliary plug-in charger for when you have external power (depends on what the coach has for converter). Start with 1-2 12v AGMs, whatever the budget can handle, abd build up.
Click to expand...
All of this discussion has really adjusted the plan but thats why I went to a forum. Heres my though process... I need to replace the old flooded battery anyways so I'm going to start there. Then get 3-4 small 12v fans and a $20 spool of wire. I have a small inverter I can continue to use for a TV. I also have the portable 100w solar panel that would go a lot farther on a 100ab agm than a 200ah agm. I think that's the place to start and expand to that bigger setup down the road after some experimenting and data gathering.
 
You say your rv is a class C. What chassis? What is your available payload? Often E350 based class CS are close to payload when built. Batteries are heavy.
 
One thing to remember is that although a 2000W inverter/charger may be overkill on the inverter side, it will have a much larger charger and that can mean less time plugged into shore power OR less time running a genny to replenish the battery bank.

As an example a 2000W Xantrex inverter/charger has a 100Amp DC charging rating, That fills up two 90AH batteries pretty good in less than a couple of hours. Not full or topped off but with enough juice for another day or two. It's true I don't need 2000W from the inverter but if I use the Xantrex 1500W inverter/charger I only get a 75Amp DC charge rating so it takes three hours of genny to fill my battery bank.

Here's the kicker... if you open them side by side they look identical, because they almost are, what you'll find is that the 2000W unit has 20 power transistors and the 1500W has 16 with four locations left blank. The rest is the same.

If you buy the 2000W it will simply run cooler than the 1500W for the same load and be less likely to overheat or fail.

There are software settings on the better inverters that will allow them to go to sleep and only wake when a load is presented, this minimizes the idle draw problem that older units had.

I say go for the bigger inverter/charger!
 
JayArr said:
One thing to remember is that although a 2000W inverter/charger may be overkill on the inverter side, it will have a much larger charger and that can mean less time plugged into shore power OR less time running a genny to replenish the battery bank.

As an example a 2000W Xantrex inverter/charger has a 100Amp DC charging rating, That fills up two 90AH batteries pretty good in less than a couple of hours. Not full or topped off but with enough juice for another day or two. It's true I don't need 2000W from the inverter but if I use the Xantrex 1500W inverter/charger I only get a 75Amp DC charge rating so it takes three hours of genny to fill my battery bank.

Here's the kicker... if you open them side by side they look identical, because they almost are, what you'll find is that the 2000W unit has 20 power transistors and the 1500W has 16 with four locations left blank. The rest is the same.

If you buy the 2000W it will simply run cooler than the 1500W for the same load and be less likely to overheat or fail.

There are software settings on the better inverters that will allow them to go to sleep and only wake when a load is presented, this minimizes the idle draw problem that older units had.

I say go for the bigger inverter/charger!
Click to expand...
I am curious, what is the idle current on modern inverters such as these?
 
You must log in or register to reply here.

Latest posts

Members online

Total: 384 (members: 9, guests: 375)

Forum statistics

Threads
132,190
Posts
1,391,770
Members
137,900
Latest member
RVMan78
Back
Top Bottom