Do these batteries look appropriate? Great deal.

[Mike90250]

We can say
"oh, great, a splendid setup, wish I had one as big"
but that conveys no data. Yes, some members are quick with a slapper, and just because something has become "standard practice" doesn't mean it's correct or proper or Best Practice.

Plumbers stack 2 wax rings on toilets all the time to cover up a mismatch. 10 years down the line the john falls through the rotted floorboard. Gee, the plumbers job looked good.

[nebster]

We can say
"oh, great, a splendid setup, wish I had one as big"
but that conveys no data. Yes, some members are quick with a slapper, and just because something has become "standard practice" doesn't mean it's correct or proper or Best Practice.

The "slappers" could be discouraged via moderation, but instead the caustic atmosphere here is abetted. Little "data" is being conveyed when people are regularly so snarky, dismissive, or rude, either, Mike. It also alienates a percentage of the forum readers, myself included. This is my last post on this thread.

Industry standard in large lead-acid RV energy systems today is as I described above. There are reasons -- including, no doubt, inertia -- why they use this approach. Redundancy and serviceability are certainly part of the equation here.

There is no "correct" or "incorrect," when in reality a system simply is one with tradeoffs.

I did not mean to suggest that the way large RV packs are delivered from the factory is "best practice" -- indeed, that industry is ripe with questionable practices propagated over decades of doing things the way they were done before. My point in identifying the largest batteries on production RVs was to help the OP see that he may (or may not) be overestimating his energy requirements, not to lay out a treatise on the best way to design a battery. I see that my choice of phrasing ("gold standard") may have been misleading, and I regret it. It was made in haste, when writing a quick response wherein I was hoping to be helpful.

That said, I do not immediately agree that another pack topology would be better, and in particular 6s 2V cells would be problematic in many ways on an RV. I think there are good reasons why virtually no one does it that way today.

[littleharbor]

The "slappers" could be discouraged via moderation, but instead the caustic atmosphere here is abetted. Little "data" is being conveyed when people are regularly so snarky, dismissive, or rude, either, Mike. It also alienates a percentage of the forum readers, myself included. This is my last post on this thread.

Industry standard in large lead-acid RV energy systems today is as I described above. There are reasons -- including, no doubt, inertia -- why they use this approach. Redundancy and serviceability are certainly part of the equation here.

There is no "correct" or "incorrect," when in reality a system simply is one with tradeoffs.

I did not mean to suggest that the way large RV packs are delivered from the factory is "best practice" -- indeed, that industry is ripe with questionable practices propagated over decades of doing things the way they were done before. My point in identifying the largest batteries on production RVs was to help the OP see that he may (or may not) be overestimating his energy requirements, not to lay out a treatise on the best way to design a battery. I see that my choice of phrasing ("gold standard") may have been misleading, and I regret it. It was made in haste, when writing a quick response wherein I was hoping to be helpful.

That said, I do not immediately agree that another pack topology would be better, and in particular 6s 2V cells would be problematic in many ways on an RV. I think there are good reasons why virtually no one does it that way today.

My 6, 2 volt example was emphasizing the fact that you can get that much power into your class A RV in a single string which is the standard recommended way to wire up a stationary battery bank whenever possible. 6 parallel batteries on the other hand is quite problematic and pretty much universally agreed upon as a poor practice in any regularly cycled battery. The RV world, or at least manufacturers, may not adhere to these standards and a 2s3p bank can be managed but my point in my previous post was pertaining to your 6p battery bank being unnecessary and frankly quite an amateurish way to approach a battery installation.

[Sunking]

(As it happens, my LFP array is 16s6p, which by coincidence is six parallel batteries. And I know exactly what I'm doing, Sunking.)

That has nothing to do with lead acid and not wired the same.

[Sunking]

That said, I do not immediately agree that another pack topology would be better, and in particular 6s 2V cells would be problematic in many ways on an RV. I think there are good reasons why virtually no one does it that way today.

Beg your pardon. Every user of large Amp Hour batteries use 2-volt cells. Perhaps ignorance and lack of experience is why you never heard of anyone using them. In my profession, it is a very rare occurrence I would ever use anything except 2-volt jars. Last time I scratched off on paper up around 1 million tons of batteries installed. Just one job alone can be as much as 100 tons. Parallel batteries are fine in Emergency Stand-By Stand By Float service, but the worse thing you can do in a daily cycled system.

But I will say this, in an RV assuming you do not use them frequently and park them with Float Chargers, you can get away with parallel arrangements. Calendar life will kill the batteries off before cycle life. But if you use the RV frequently or living in one, you are killing your batteries with parallel arrangements needlessly. If Inertia or Spills is your issue, then I suggest you learn about AGM batteries.

[zamboni]

I'm a full-timer in an RV with LFP batteries, and if i were doing what the OP wants to do, i would choose FLA batteries, absolutely. LFP simply isn't needed for that kind of application, costs too much, is too risky, and demands more attention. It's bringing a glass cannon to a rock-throwing contest (if i may abuse a metaphor). I think about my LFP batteries every single day, whether i want to or not. I also describe my lifestyle as "living inside an experiment" - so it's my choice - but that does not describe a typical fulltimer's mentality. If you feel the need to spend money to make your rig cooler, they have those light-up LED flagpoles...

In the fulltime RV world "got lithium" is a hot thing and everyone with a few bucks wants it, even if they can't really say why. The good installers are booked out 1+ year; who knows about the not-good ones. The ensuing fervor rubs off on everyone and nobody in that circle is understating or communicating the risks. The BattleBorn drop ins are not helping. I don't know enough about them to praise or criticize, but their very existence makes LFP seem "easy" and "safe", and that impression is being applied - as these things are - with a broad brush to LFP in RVs on the whole. While the technology is exciting, this whole situation worries the hell out of me. My thread asking about LFP fire suppression is honestly less for myself and more for someone else's rig that i may come across one day (at least, i hope it is).

This whole conversation is hard because 1. It's very difficult to elucidate to newcomers (or even experienced people) the challenges/risks and 2. There is strong community pressure generating interest in people who would not otherwise be playing at the edge of a technology like this. So you've got these grizzled veterans trying to make a bunch of teenagers believe their impassioned, genuine warnings, and it goes the same way those conversations always do: The ones who know end up making terse, unexplained, exaggerated-sounding threats and declarations...and the teenagers, who already assume the experts are old and out-of-touch, write off the advice.

And that problem is as old as humanity...so i don't think we're gonna solve it on SolarPanelTalk. I thought maybe explaining where all these RVers are coming from might help the communication flow a bit better?


- Jerud
------------------------------------------------------------
1220W array / 1000Ah LFP house bank
MidniteSolar Classic, Magnum MS2812
ME-RC, Trimetric, and JLD404
2001 Fleetwood Prowler 5th wheel 25 foot, self-rebuilt
Full-time 100% electric boondocking (no propane, no genny) since 2015

https://www.livesmallridefree.com

[OldSmokey]

My 6, 2 volt example was emphasizing the fact that you can get that much power into your class A RV in a single string which is the standard recommended way to wire up a stationary battery bank whenever possible. 6 parallel batteries on the other hand is quite problematic and pretty much universally agreed upon as a poor practice in any regularly cycled battery. The RV world, or at least manufacturers, may not adhere to these standards and a 2s3p bank can be managed but my point in my previous post was pertaining to your 6p battery bank being unnecessary and frankly quite an amateurish way to approach a battery installation.

RV'ers are a special breed of "Luddite" when it comes down to batteries and solar. basically if you don't speak "12 Volts, 4/0 cables and 3000 Watt inverters" then there is something odd with you !!

[rw3iss]

Cool, guys, learning here, in more ways than one, heh. Thanks!
I didn't know there were such concerns with series vs. parallel, for one.
It's looking like I'd be better off going FLA in a completely series configuration, but will research more on that.
I'm not entirely sure if I'm better off running the battery bank at 12V, or 48V, for that reason. I need to read up on the tradeoffs of the different voltage sizes again.

With that said, if I wanted 10kwh reserve, (and I know I should be doing my own research here, and plan to/am), in a series configuration, what does this mean in terms of individual pack voltage?
I think this would mean I'd need something like:
@12V system = 10kwh / 12V = 830Ah = something like x6 2V 200Ah per battery = 12V 200ah "lines" (2.4kwh), then would need to put ~4 of those configuration in parallel to reach the total ~800Ah? Is that how it should go? How do people achieve the higher bank Ah capacities here without resorting to parallel configurations, or do they?
Otherwise:
@ 48V system = 10kwh / 48V = 208Ah = something like x24 2V 200Ah batteries

Edit: noticing all the sticky threads I haven't read yet that probably answer all of this, so please forgive, gettin' on it...

[OldSmokey]

@ 48V system = 10kwh / 48V = 208Ah = something like x24 2V 200Ah batteries

or eight T105's ?

[zamboni]

I might as well be the one to say it: Make sure your 10kWh target battery size is the result of a detailed energy audit, not back-of-napkin estimates. Putting the time into a really good audit pays off repeatedly, at every step of the process (including the one where you get to use it). As a reference point, my rather-big-for-an-RV battery is 12kWh and i don't use any propane in my rig. Now, i do live simply...but assuming you're planning to keep the propane, i'd wager you're shopping for too much battery. Also remember your array needs to scale with the batteries -- you're looking at 1000+W of panel to support that many. Have you evaluated your available roof space?

Based only on your earlier statement of max 750W inverter load (assuming it is max simultaneous, not max for a single device), a 12V bank will probably be the best choice in an RV since you need 12V for so much other stuff, and the components are easy to find.

[rw3iss]

Thanks for chiming in, zamboni, useful stuff, and nice to hear someone else doing what I'm about to do. I will plan for a 12V system, as, yeah, it makes sense in an RV.
Here's the breakdown of my power usage:

Lights: ~200W total in the RV. On for 5-6 hours a day max.
Water: powered by 90W pump, only on when using water (let's say 1 hour a day?)
Laptop: ~90W power adapter. Generally on this thing a lot, let's say 8 hours a day (more now, but traveling, I assume that will decrease).
Phone: using as hotspot, will need to keep plugged in = 10W for ~12 hours day
Speakers: 120W x 2 = 240W, plus about 200W max from the subwoofer and its amp, and then I have an audio interface that uses 24W = ~470W total, probably on for 6 hours out of a day.
Misc: random power tools, things I'm using occasionally when working on projects, let's say 200W, for 1 hour a day.

Total power per day:
+200W for 6 hours = 1200Wh
+90W for 1 hour = 90Wh
+90W for 8 hours = 720Wh
+10W for 12 hours = 120Wh
+470W for 6 hours = 2820Wh
+200W for 1 hour = 200Wh

TOTAL: 5150Wh / day

With that said, seeing as I'd be smart to have a battery bank that won't see < 50% DOD, 10kwh seems like a good mark, especially considering I should plan for reserves. Yeah?

As for the solar panels, yeah, I had planned to have about 1500W on the roof. There should be plenty of room for 6*250W or 300W panels. I also had ideas to put them on the sides, on hinges, that I'd prop up when stationary, but only if that's necessary.

@OldSmokey... the T-105 is a 6V battery? What's the deal here, guys? Should I not have any batteries in parallel at all, or is that always going to be a requirement at some point, to meet the 12V, whatever Ah I need (10kwh @ 12v = ~800Ah). With a 6V battery, I'd go in series twice, then everything else in parallel. I'm a little confused as I don't see a way around having to do some in parallel.

[zamboni]

Don't forget your fridge will draw some for the control board, and if you run the furnace for heat the fan is evidently greedy - i have neither but always hear fellow RVers complaining about these two : ).

A few suggested modifications to your assumptions:

• Are your lights LED? If i turn every light in my rig on at once, i barely draw 6A - 72W - and that includes two non-LED reading lamps.
• Find a 12V --> 5V (USB) socket to keep the inverter from having to run just to charge your phone and run it as hotspot.
• Use a "cigarette lighter" power supply instead of running the inverter to power the laptop's brick. Not a practical option for macs, unfortunately, due to lack of available accessories.
• Water pump will be ~3gpm. We consume approx. 3gal/person/day with "comfortable" (for boondocking) usage. So our pump only runs a total of a few minutes a day. I expect yours won't be much more than 5 total.
• Are the power tools corded or cordless? If you're running corded you may want to ensure the inverter is pure-sine (more $). Cordless generally works out better 'cuz they don't end up influencing your system size and you can stick with a mod-sine inverter. Also, don't need an extension cord ; )
• Your math seems to be assuming absolutely zero solar input for the day. Depending on the kind of weather you expect to operate in, your panels' output should generally cover your instantaneous usage -- plus extra to recharge the batteries (from overnight).
• You want to find ways to keep the inverter off as much as possible, and then while it's on, to make sure it's "earning it's keep". Idling the inverter so it can trickle 10W to keep a stereo in 'standby' will waste a lot.

Keep in mind that living off-grid does require a shift away from the "always-there electricity" mentality most of us are accustomed to. While you are inside a house and someone describes it to you, it sounds like they're talking about the Dark Ages. But once you live this way for a short while, you realize it's quite manageable - and that "normal" is pretty damn wasteful. That said, you could make things a lot easier on yourself if you dial back the audio equipment...if that is a priority for you then okay -- but RVs are small and have very thin walls. It doesn't generally take a lot of power to "rock the house". Consider downsizing the audio: car audio components can run directly off 12V and last i checked they can put out plenty of noise. Alternatively, if the high-wattage equipment is important to you, accept using it for extended periods only on sunny days when you have surplus power.

Pick up a Kill-a-watt meter (less than $20) and measure your actual use of AC power. Measure for an actual "all day" period, don't just take one instantaneous reading and multiply it out. You will find that few devices actually run at nameplate wattages steady-state; some operate well below nameplate for the bulk of the time. Nameplates are for safety not solar sizing : )

Re: 6V batteries...the reality is that you will probably end up with parallel strings of 6V batteries, even though we all know it's a bad idea. The practical effect is they won't live as long as they should...but the warranty period on T105s is longer than most RVs last...so this bit of battery abuse generally gets overlooked. The form factor is an issue and RVs aren't built for smart solar. If you can find a way to fit 6x 2V cells into your whatever-compartment then by all means go for it. Also: don't blow your wad on your first set of batteries because there's an excellent chance you'll abuse them, no matter how careful you try to be (another excellent reason to avoid LFP at this point).

Do make sure you read those stickies - great info in there and sometimes reading the same info in a different formal helps it sink in.

[littleharbor]

Satellite TV receivers draw almost as much power when "off" than when you're watching TV. I always switch off the power to them when not actually using them. They don't take long to boot up and you'll save a fair amount of power , especially if you don't watch much TV. I don't see TV listed in your daily load estimate so maybe a moot point. Still viable info for others who may be reading this thread.

Maybe the newer cordless tool batteries and chargers are more tolerant than the older tech. but I must mention that I ruined a half dozen Makita 9.6 volt batteries using a MSW inverter. This was over the course of a couple days, not weeks or months.

[bcroe]

Satellite TV receivers draw almost as much power when "off" than when you're watching TV.

Maybe the newer cordless tool batteries and chargers are more tolerant than the older tech. but I must mention that I ruined
a half dozen Makita 9.6 volt batteries using a MSW inverter. This was over the course of a couple days, not weeks or months.

A lot of stuff got REAL off-on switches for energy conservation here. Perhaps the problem charging the
batteries was actually a poor, inflexible charger design. Its usually overlooked, that a square wave is actually
the ideal input waveform for a rectifier. Bruce Roe

[Sunking]

Cool, guys, learning here, in more ways than one, heh. Thanks!
I didn't know there were such concerns with series vs. parallel, for one.
It's looking like I'd be better off going FLA in a completely series configuration, but will research more on that.
I'm not entirely sure if I'm better off running the battery bank at 12V, or 48V, for that reason. I need to read up on the tradeoffs of the different voltage sizes again.)

Now you are starting to ask good questions and the lights will start turning on for you. There are boundaries, and RV like to go outside the lines. Lets start with the 12 volt thing. RV's are unique as there are a lot of 12 volt gizmos made for them. Unfortunately they are not usually efficient, but I digress because I do not care. 12 volt solar is power limited period. Realistically the largest MPPT charge controller you can find is 80 amps. Charge Controllers have an Input Power Limit based on Current Output vs Battery Voltage and generically looks like this.

1000 watts @ 12 volts
2000 watts @ 24 Volts
4000 watts @ 48 volts.

So there is your first limits.

All batteries have limits and this is where most get into a lot of trouble. Batteries have minimum and maximum charge/discharge limits. For RV minimum charge requirements is easy, any slower than C/10 is too slow. So if you have an 200 AH battery, no slower than 20 amps or the 10 hour rate. On a 12 volt system is going to require 20 amps x 13 volts = 250 to 260 watts. On the Flip side you do not want to charge to fast. For FLA depends a bi ton the battery. Stationary Systems C/8 would normally be as fast as you want for a 5 day reserve. RV needs to go a bit faster because you typically design for 3 day reserve so as fast as C6. Same applies to max discharge rates. Put too much load on a battery, and the voltage collapses and your Inverter will shut off despite having a charged battery. So with a good set of Trojan Golf Cart Batteries which is a hybrid you can discharge as fast as C/5, so a on 220 AH battery is 45 amps. If that is a 12 volt Inverter we are talking a 12 volts x 45 amps = 540 watts. How many of you RVer's out there have 2000 watt Inverters with a pair of golf cart batteries and a 2000 watt Inverter? I digress, I don't care what you do.

One thing you can do is think about is AGM batteries. Reason is simple they have much lower Internal Resistance and can take much larger charge and discharge currents. They also do not splill and some can be mounted in unusual orientation to make them fit like on their sides. They weigh less and a bit smaller for a given capacity. Just about any AGM can do C/4 and the better ones like Concord and Odyssey can easily handle C/2 currents better than Lithium. Even Trojan makes a decent AGM. So with a 12 volt 200 AH system now you can use that 1000 watt Inverter that draws 100 amps.

Now lets talk about the Killer in a low voltage system. CURRENT, and most RVer's are clueless about it, and do not know how to work with it. You were taught wrong all you life voltage is the Killer and ignorant about current. A short circuited battery can deliver thousands of amps. I am going to make it real simple NO FUSE GREATER than 100 AMPS and NO CONDUCTORS larger than 2 AWG. Here is what that means for you. 12 volts no larger than 1000 watts, 24 volts no larger than 2000 watts, and 48 volts no larger than 4000 watts. Kind of funny how that matches up with Charge Controller huh? Do you think that is accident or by design? I really do not care if you burn up your RV. But I can tel you right now you are not qualified to work with any conductors larger than 2 AWG and most of you are not even qualified to work with small telephone cable. You just do not have to tools, do not know a proper from a chi-com POS compression terminal o how to use them. Couple that lack of knowledge of how dangerous high current is and you have a recipe for a fire. I suggest you buy factory made cables. I digress, I do not care what you do.

Lastly start connecting the dots and seeing the limits lined out there. That is how we know immediately most of you do not know what you are doing. You will notice things like panel wattage should roughly = Inverter wattage, no battery larger than 800 AH. I digress.