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Is this still current thinking for an RV?

TommyDKY

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Nov 18, 2020
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Looking to build a LifePo4 battery for an RV and was thinking of using 8-272AH cells for 2-12v 272ah in parallel for 544AH@12V total. I have run across some interesting articles posted on this forum and was wondering if the information below (#1&#2) is still the current and up to date view of LifePo4 battery technology? I have 1120w of solar

1. "The first consequence of installing an oversize battery bank, especially when sustained charging is involved as with solar panels, is that the bank remains at a higher state of charge much longer, if not most of the time. This is very detrimental to its ageing for reasons that were developed earlier. Lithium cells like cycling because it means they don’t spend any amount of time near full; alternatively, they can sit happily
half-discharged, or even lower, for years."

If this is true how do you keep the batteries from the full charge to protect them?? Would you set your float charge to equal 90%SOC??

2. "Single 3.2V prismatic LiFePO4 cells can nowadays be obtained in huge capacity, as high as 10000Ah. Commonly available cells range between 40Ah and maybe 1000Ah. It should be pointed out that the larger sizes are intended for stationary applications where no accelerations, vibrations or shocks are ever experienced.
A sales manager at Sinopoly I was talking to was adamant about using 100Ah or 200Ah cells only for assembling marine battery banks, with 100Ah being preferred and 200Ah acceptable. Large cells simply don’t have the structural strength-to-weight ratio required to be taken to sea on board small crafts and would exhibit shortened life due to internal mechanical damage arising from on-going vessel motion. It is common sense: as a cell becomes larger, its internal weight increases much faster than the rigidity and surface area of the casing and the casing is all what holds the plates together in a prismatic cell.
Failures have been reported on vessels equipped with 700Ah cells following ocean passages: some cells were suddenly found to be losing charge inexplicably, rendering the battery bank completely unmanageable and the matter ended in a complete write-off. All big-brand commercial marine lithium battery packs on the market today are built from cells no larger than 200Ah."

So is it not a good Idea to use 272AH cells in a build for an RV?
 

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Welcome to the forum.

#1) kinda true. LFP should be stored for longer periods of time at lower states of charge.

HOWEVER, even shallow cycling counts. Furthermore, I'm almost willing to bet you what you'll figure out you have more capacity and you'll use it accordingly. :)

If you care a lot, you can alter your charge profile to only charge to a ~80-90% SoC. Prior to storage, you can discharge them to ~50%.

#2) The Eve/Lishen, etc. cells recommend compressing/clamping them for maximum life. Suitably clamped, protected from abrasion with some effort to minimize shock should minimize any vibration related issues.

Many use 272/280Ah cells in RV installations.

@HRTKD basically has your setup in his 5th wheel.
 
Well good idea or not - I am going to try it. First, RV’s move much less than marine. RV’s only move when being driven, and even the worst roads are not as bad as the waves. Boats move most of the time and on passage move LOTS!

Second, I am planning on the same batteries you are - eight 272ah lishen’s - hooked up into one large battery. My plans will be to have my water heater automatically run on electric if the State of charge is above 50%. Also if above 50% run the fridge on electric rather than propane. Those two changes will mean keeping the batteries off of 100% full most of the time. When not living in RV drain batteries to 50% then shut everything down.
 
Welcome to the forum.

#1) kinda true. LFP should be stored for longer periods of time at lower states of charge.

HOWEVER, even shallow cycling counts. Furthermore, I'm almost willing to bet you what you'll figure out you have more capacity and you'll use it accordingly. :)

If you care a lot, you can alter your charge profile to only charge to a ~80-90% SoC. Prior to storage, you can discharge them to ~50%.

#2) The Eve/Lishen, etc. cells recommend compressing/clamping them for maximum life. Suitably clamped, protected from abrasion with some effort to minimize shock should minimize any vibration related issues.

Many use 272/280Ah cells in RV installations.

@HRTKD basically has your setup in his 5th wheel.
Saw this post of yours earlier in another thread and I would like your opinion on what size BMS I will need “Depends on your needed load. The current limit of the BMS will be the ultimate limit on battery performance. 3000W/12V = 250A”

Looking to build a LifePo4 battery for an RV and ordered 8-271AH CATL on the group buy. Would like to build cells for 2-12v 271ah in parallel for 542AH@12V total. What size bms do you recommend? Like the ones from overkillsolar.com?
 
(Inverter power) / 12V = needed current.

If you build 2X 12V w/120A Overkill, that's 240A

240A * 12V = 2880W
 
I built an oversized pack and just set the charge limits very conservatively. In general, I know when I will likely need more power and simply charge to a higher SOC when needed - which is not too often so far. I like having the option. I would say I am generally cycling between 30% and 80%.

On a recent long road trip, I knew it was going to be difficult to charge for about 3 days so I topped it off to about 95% to give myself a solid shot at making the 3 days solely on battery.
 
Welcome to the forum.

#1) kinda true. LFP should be stored for longer periods of time at lower states of charge.

HOWEVER, even shallow cycling counts. Furthermore, I'm almost willing to bet you what you'll figure out you have more capacity and you'll use it accordingly. :)

If you care a lot, you can alter your charge profile to only charge to a ~80-90% SoC. Prior to storage, you can discharge them to ~50%.

#2) The Eve/Lishen, etc. cells recommend compressing/clamping them for maximum life. Suitably clamped, protected from abrasion with some effort to minimize shock should minimize any vibration related issues.

Many use 272/280Ah cells in RV installations.

@HRTKD basically has your setup in his 5th wheel.
Read you can use the nylon banding material to clamp the batteries?? What do you recommend?
 
The term “RV” is becoming more and more common these days, but for some, myself included, was wondering what RV stands for? RV really stands for adventure. It offers the flexibility and freedom to enjoy life's greatest pleasures that only Mother Nature can provide. I was able to take my family, including my beloved pets, on adventures and create many wonderful memories along the way.
RV = Recreational Vehicle
 
I've studied decision problems in the face of uncertainty, and the decision problems posted on this forum are as difficult as they get. :(

As a first step you should make up a Consequences Matrix.
 
The term “RV” is becoming more and more common these days, but for some, myself included, was wondering what RV stands for? RV really stands for adventure. It offers the flexibility and freedom to enjoy life's greatest pleasures that only Mother Nature can provide. I was able to take my family, including my beloved pets, on adventures and create many wonderful memories along the way.
An RV is a "R"ecreational "V"ehicle. Some units sit in a park for months or forever, some of them move every day or two. One persons adventure is another person nightmare. Even the recreation part is meaningless as more are living in the units, either from choice or need.

SUV is supposed to be Sport Utility Vehicle but most have never had their tires off the pavement :)
 
I've studied decision problems in the face of uncertainty, and the decision problems posted on this forum are as difficult as they get. :(

As a first step you should make up a Consequences Matrix.
Or just quit with the paralysis by analysis and just build a system. If it's wrong then change it. LOL

For further info see the Cell Clamping thread
 
Or just quit with the paralysis by analysis and just build a system. If it's wrong then change it. LOL

For further info see the Cell Clamping thread
I'm a cheapskate! :(

But now I have money but not much time so I'm wary of chasing wild geese.

If it:
-works on paper it still may not work in the real world.
-doesn't work on paper it will not work in the real world.
 
I'm a cheapskate! :(

But now I have money but not much time so I'm wary of chasing wild geese.

If it:
-works on paper it still may not work in the real world.
-doesn't work on paper it will not work in the real world.
Just boil it down to some basics:

- determine avg usage (not peak, live with less on cloudy days)
- if you're really cheap with a short view for the system then use FLA
- for an RV a 2kw inverter is usually plenty and provides equivalent to a 15A outlet with some headroom
- 300Ah of Li is pretty good
- Ah * 2 = watts of panels
- use your existing DC converter to charge when needed, even a non-Li unit is fine just monitor the battery voltage
- cheaper h/w works fine, not everyone needs to drink the Victron or Battleborn KoolAid
- lots of charts will provide DC ampacity to size cables, just keep them short and neat

That's my take on it all. I started 7 yrs ago with FullRiver 6v AGMs, 320w panels, 2kw Xantrex and EPSolar MPPT. Now I have 560Ah self-built Li, 640w of panels, 3kw Renogy and Renogy Rover MPPT. Still using the onboard non-Li DC converter. Also I sold the AGMs last summer for 25% of what I paid for them 7 yrs ago
 
The term “RV” is becoming more and more common these days, but for some, myself included, was wondering what RV stands for? RV really stands for adventure. It offers the flexibility and freedom to enjoy life's greatest pleasures that only Mother Nature can provide. I was able to take my family, including my beloved pets, on adventures and create many wonderful memories along the way.
What is commonly called a 'necro-post'. New post on a thread over a year old. [shrug]
 
I'm a cheapskate! :(
In a lot of cases the least expensive option is doing it right the first time.
I think a lot of folks end up doing it twice.
Cheap stuff the first time and not so cheap the second time.

Take your time, read voraciously and ask questions.
There are lots of people here who can give you the benefit of there experience.

As others have said, a successful project starts with defining requirements.
 
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