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Discussion Starter #1
I'm looking to make a storage battery for a camper. Lithium is a better value for the money than lead IMO.

I want a 12v 400AH lithium pack as simple as can be. Fewer cells is better, isn't it? So, that's four 400AH cells I need plus a BMS.

I've heard prices are as low as $0.85/ AH if not in a hurry. Is that correct? Suggestion or comments?

Thanks!
-John
 

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Fewer cells sounds better, but in practice I don't think that you will be able to get cells that large, at least at a reasonable price. I suggest just parallelling enough cells at the lowest level to reach your desired 400 Ah capacity, then stacking four of those sets in series to get a suitable voltage.

The cheapest source of lithium cells is probably salvaged EV battery packs; however, they may not be the desired chemistry. For RV applications LiFePO4 is often preferred, but it is not commonly used in EVs.

I have considered using Nissan Leaf modules for an RV or travel trailer. A challenge is that they are 2s2p in configuration (33 Ah per cell in the first generation, so 66 Ah and 7.5 volts per module), so they can't be combined in parallel at the cell level unless you also parallel the BMS terminals, and ensure the any current imbalance is not excessive for those smaller terminals. Only two modules would be needed for "12 volts", but a dozen modules would be needed for about the desired capacity - if they were all stacked together that would be a stack sized
11.9" (303 mm) x 8.8" (223 mm) x 16.5" (420 mm)
and 101 lbs (45.6 kgs)

Any of the pouch cell EV batteries using larger modules will be difficult to reconfigure for the desired voltage. The prismatic cells of the German brands should be easier to work with, especially the Sanyo 25 Ah cells originally used in the VW e-Golf (which has since changed to Samsung SDI) because those Samsung cells have threaded terminals (easy to build jumpers and cables). Of course with 25 Ah cells you would need (400/25)x4=64 of them.

Keep in mind that the normal operating voltage of a series set of four lithium cells - even LiFePO4 but especially automotive chemistries - is very high for the nominally 12 volt systems of an RV, and the charging voltage is even higher. You might consider a DC-to-DC regulated power supply (set for no more than 13.2 volts) for at least the more sensitive equipment. I find that furnaces make a lot of noise and may have problems even at common lead-acid charging voltage.
 

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I would not recommend EV packs or second-hand cylindricals etc, in fact any chemistry but LFP for House bank usage in a mobile living space.

New quality large LFP prismatics go for $7-9 /AH before shipping, in the US market.

Do not go Alibaba direct from China, if NG you gonna pay to ship them back? Lotsa scammers out there.

Cheapest quality deep cycle **FLA** is $1 / AH.
 

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I would not recommend EV packs or second-hand cylindricals etc, in fact any chemistry but LFP for House bank usage in a mobile living space.
Few RVs put the battery in the living space. they're usually on the tongue of a travel trailer, or under the floor of a motorhome. "Camper" could mean just about anything; if it means a slide-in unit carried by a pickup truck... then those have the battery within the coach body, but they should still be externally vented and sealed from the living space.

As I said, LiFePO4 (a.k.a. LFP) are commonly preferred for RVs. I think there are multiple reasons for this, including:
  • lack of any thermal management
  • low importance of power density
  • better voltage match to 6-cell lead-acid
 

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New quality large LFP prismatics go for $7-9 /AH before shipping, in the US market.
Are CALB cells of the quality that you're describing? They're well under $2/AH per cell, which would be less than $7-9 /AH for 4 cells in series.

That's a couple thousand dollars, before shipping, interconnections, BMS, and housing.

Cheapest quality deep cycle **FLA** is $1 / AH.
That would be at 12 volts, not single-cell, right? I assume that the expected $0.85/ AH is for a single cell (or parallel group of cells), not for a stack of them to reach 12 volts.
 

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Discussion Starter #6
I should have clarified the lithium type upfront. I am looking at LFP (lifepo4) cells. I have experience building HV packs for golf carts using leaf modules. They are not conducive to 12v usage because of their 2p2s module.

Also, the "expected" $0.85/ AH is for a single cell, not the desired whole pack. With just quick searches, I found 400AH LFP cells between $1/ AH and $1.30/ AH. I don't know shipping for just four cells, it could be high.

I won't use FLA, although cheap they are. I don't want to build a sealed enclosure for the gassing smell and they take up a lot of space.

I considered AGM. No gassing problem and they can be side mounted but space is still needed. If you compare usable AH from AGM to LFP, the LFP wins easily.

Drop-in 12v lithium batteries (battleborn, etc,...) are still very expensive. I bet I can build a LFP pack much cheaper.

Use will be a house battery for a campervan conversion. Sort of RV I guess. Think of a DIY Class B RV. I want power abailable and a 12v 400AH pack would do nicely. 600AH would be even better but it's even more money and cells.
 

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Discussion Starter #8 (Edited)
I'd need eight CALB 180's and it would be short of 400AH. :)

The cells I'm looking at are LFP 400AH made by GBSystem. About $1/ AH plus shipping.

I am in Savannah, GA
 

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Drop-in 12v lithium batteries (battleborn, etc,...) are still very expensive. I bet I can build a LFP pack much cheaper.
I agree. These off-the-shelf batteries incorporate an internal BMS, and combining four of them (100 Ah @ "12V" is typical) results in an excessively complex BMS and housings. Also, they are marketed to people who have no clue what is inside, just want a drop-in replacement for common 12 V lead-acid batteries, and are willing to pay a lot for increased performance.

Use will be a house battery for a campervan conversion. Sort of RV I guess. Think of a DIY Class B RV. I want power abailable and a 12v 400AH pack would do nicely. 600AH would be even better but it's even more money and cells.
Any RV conversion of a van is a Class B. 400 Ah (@ "12V") is huge capacity for Class B (similar to four "golf cart" batteries), but some people do it, especially if they are planning for refrigeration and cooking to be done electrically. RoadTrek offers even larger in their optional EcoTrek systems.

In a larger motorhome the battery can go under the floor, but in a van it will likely end up on top of the floor, under the bed. Please enclose and vent it appropriately.
 

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Discussion Starter #11 (Edited)
It’s only Class B of built by a RV manufacture and titled Class B. Self conversions are still just vans. 😁

Yes 400AH is large, I can afford it and the power will be used. Heck, one day I may add another 400AH in parallel for super power.

CALB 400AH look to be around $500 each. The GBSystem 400AH are $400 each. Much better deal for same capacity and similar specs. Anyone seen 400AH cells for a better price?
 

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Discussion Starter #12
In a larger motorhome the battery can go under the floor, but in a van it will likely end up on top of the floor, under the bed. Please enclose and vent it appropriately.
I am converting a small van, under 21 feet length. I still will probably install house battery under the floor. Really depends on the house battery I end up getting.
 

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I am converting a small van, under 21 feet length. I still will probably install house battery under the floor. Really depends on the house battery I end up getting.
Great if you can do it, but good luck with that. The traditional rear-wheel-drive vans fill much of the underfloor space with propeller shaft, fuel tank, and exhaust system... and the remaining space is broken up by the frame and body structure. In what's left, you would ideally want to mount the fresh water tank, grey waste tank, possibly black waste tank, maybe generator, perhaps furnace and/or water heater... and the battery. The Ram ProMaster (Fiat Ducato) is front-wheel-drive and puts the fuel tank under the front seats, so it's a bit better for usable space underneath. What van are you planning to use?

It's easier to build fluid tanks (fresh and waste water) to conform to the available spaces under the floor than to package large rigid blocks of cells to fit.
 

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It’s only Class B of built by a RV manufacture and titled Class B. Self conversions are still just vans.
No, the classes are just descriptions of recreational vehicle configurations. Lots of people have built Class C motorhomes, and they're still Class C motorhomes, not just trucks. But it's yours, so I suppose that you can call it what you want. :)

By the way, the most impressive home-built Class C that I've seen is shachagra.
 

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Discussion Starter #15
Great if you can do it, but good luck with that. The traditional rear-wheel-drive vans fill much of the underfloor space with propeller shaft, fuel tank, and exhaust system... and the remaining space is broken up by the frame and body structure. In what's left, you would ideally want to mount the fresh water tank, grey waste tank, possibly black waste tank, maybe generator, perhaps furnace and/or water heater... and the battery. The Ram ProMaster (Fiat Ducato) is front-wheel-drive and puts the fuel tank under the front seats, so it's a bit better for usable space underneath. What van are you planning to use?

It's easier to build fluid tanks (fresh and waste water) to conform to the available spaces under the floor than to package large rigid blocks of cells to fit.
You are making a lot of assumptions in my van build. Let's stick to creating a 400AH lifepo4 house battery for this forum.

I'm still looking for the best deal source, most likely direct from China. I can wait months for the house battery as I know it's long lead time due to surface shipping, slow boat from China saying is real this time. I'm still scanning Alibaba and Aliexpress for a distributor that would deal in low quantity orders.
 

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Two strings give redundancy without buying a spare cell
Are you suggesting paired cells, four pairs in series, or two four-cell strings in parallel? Two strings would double the BMS complexity.

RVs rarely have battery redundancy, although lithium cells without widespread availability might make that wise. sportcoupe was explicitly looking for the minimum number of cells.
 

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Discussion Starter #18
Correct, four 400Ah cells in series. Simple. If I used eight 200AH cells (4S2P), it's not redundant, it's just more wiring and additional BMS. If 400AH cells are available, that's what I'll use unless there is a spectacular deal on 200AH cells.

To be redundant, I'd have to add a second house battery that came on line when the first one was drained. I don't know why you'd do that.
 
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