Correct way to build a 12v 560ah Lifep04 battery bank?

jjrox

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Dec 1, 2021
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Hoping to get some sage advice from the pros on this site.
I want to build a new 12v lifepo4 battery bank for my Class A motor home. I need about 400ah of use per day. I was thinking to build a 560ah bank using 8- 280ah cells. I plan on depleting the bank around 80% / day and that would give me some leeway on my daily amp draw and still allow the batteries to have longer life.
My first question is this a sound plan?
Second question is should I build two separate 280ah bank batteries each with it’s own BMS that would run in parallel, or one large bank with one BMS?
Third question is what would be the best BMS to use?
Fourth question is I was going to buy my lifepo4 cells on Amazon. Right now they have a bank of 4 grade A for $599. by Kimo. They also have whats advertised a 4 new grade A cells for $849. by Ninthcit. Any one have experience with these?
Thanks,
JJ
 
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What is the maximum continuous draw that you plan for?
Usually this is determined by the inverter selected.
Example: 2000 watt inverter...
2000 ac watts / .85 conversion factor / 12 volts low cutoff = 196.078431373 service amps
196.078431373 service amps / .8 fuse headroom = 245.098039216 fault amps.
That means a BMS(s) that can handle ~200 amps continuous.
If you have any significant pure dc loads those should also be factored.
 

Bob B

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1. It kinda depends on how you plan to charge the batteries. If you are using solar, you may have to size larger to get you thru days with little sun. What voltage are you planning to use?
2. Depends on what you expect your max charge and load currents to be. The single BMS would need to be able to handle that ..... If you do a 2P4S configuration, you would want to make sure you have well matched cells.
3. What will your max charge and load current and voltage be?
4. Not familiar with that seller .... there hasn't been a very good track record for cells bought from Amazon ... they would most likely be commodity grade B cells.
 
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Dzl

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Hoping to get some sage advice from the pros on this site.
I want to build a new 12v lifepo4 battery bank for my Class A motor home. I need about 400ah of use per day. I was thinking to build a 560ah bank using 8- 280ah cells. I plan on depleting the bank around 80% / day and that would give me some leeway on my daily amp draw and still allow the batteries to have longer life.
When you say 80% are you saying you plan to use 80% of the 400AH you planned to have per day, or 80% of 560Ah
My first question is this a sound plan?
Depends on the type of travel you do, your usage patterns, and your available charge sources. If you design the system for 80% DoD on an average day, that gives you not much breathing room for higher than average consumption, let alone any additional days of autonomy. Of course, if you have a generator or usually have shorepower available, maybe sizing the system for 1 day of autonomy is the sweet spot (allowing you to minimize or time shift generator use, without breaking the bank).

Second question is should I build two separate 280ah bank batteries each with it’s own BMS that would run in parallel, or one large bank with one BMS?
There are different views on this, people here generally recommend separate packs connected in parallel over the one large bank approach. But there are smart people on both sides of that conversation. Advantages of separate packs in parallel (if you do it right) are redundancy and true per cell monitoring.

Third question is what would be the best BMS to use?
There isn't a best BMS, and the ones that contend for that title tend to be above what most value-oriented DIYers can justify paying ~$500-1500.

Two of the most popular options in the budget/value-oriented category are the Daly BMS (simple, basic, relatively cheap, high current models available) or the JBD BMS (smart BMS, bluetooth, relatively cheap, a bit fuller featured, harder to find high current models).

Some fuller featured higher quality offerings include: REC, Orion, Batrium, SBMS0, 123smartBMS, Zeva and others.

If you are a beginner, overwhelmed, and just want a simple reccomendation, I would reccomend buying one of the JBD smart BMS's from the seller Overkill Solar. They can be found on Amazon or on their website. This seller offers good service/support, wrote a beginner friendly manual for the BMS, and has a good return policy. The main limitation is the highest current model they sell for a 12V BMS is 120A.

Fourth question is I was going to buy my lifepo4 cells on Amazon. Right now they have a bank of 4 grade A for $599. by Kimo. They also have whats advertised a 4 new grade A cells for $849. by Ninthcit. Any one have experience with these?
Never heard of either company, every grey market reseller calls their cells grade A, its not really predictive of whether they are or are not.
There are currently a few sources popular on the forum that people seem to trust/have mostly good experiences with. One has been around a while and has a mostly positive track record, the other is somewhat new but receiving good feedback so far and has a US warehouse. Your own due diligence is a must though, even with sellers others choose to trust, bear in mind, most people make at most one or two purchases, and most people don't do much pre-purchase vetting or post-purchase testing, so take individual positive and negative reviews with a grain of salt.

I would avoid random sellers on amazon/ebay/aliexpress for cells.
 

Rocketman

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Sep 27, 2020
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I don’t know how sage I am…


This is my story of my MotorHome batteries and BMS. I gotta say - right now I love my batteries and bms.

As for cells… I got mine from Michael Caro - before the big blowup. Right now I think the Chinese company that has USA stock in Houston, is probably the one I would look at… but I really don’t know.
 

Cajunwolf

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I don’t know how sage I am…


This is my story of my MotorHome batteries and BMS. I gotta say - right now I love my batteries and bms.

As for cells… I got mine from Michael Caro - before the big blowup. Right now I think the Chinese company that has USA stock in Houston, is probably the one I would look at… but I really don’t know.
Which Chinese company, I live in Houston and in the market for batteries.
 

Rocketman

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Now you know everything I know…

Good luck!
 
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