“Break free of 4S4P” w/ Multiple Battery Banks?

[sun_of_a...]

Thank you Zany.

 

[Brucey]

Hello, Happy New Year! Thanks so much for the forum and please check my thinking on this plan.

Apparently too much “togetherness” in DC circuits, as perhaps in life, is problematic. Is some kind of automatic battery bank switch/switcher the answer?

Please just assume for a moment someone wants to go with small LiPo batteries (100ah and 230ah) rather than larger (For ease of moving the batteries around for different applications, Eg, from the main home to a vacation home, or to a yacht to power electric engines. Also, smaller amp hour cells are said to be much better for marine) 4S4P seems a serious limitation.

So, let’s say that person envisions 3 separate 48 volt battery banks, A, B, and C, each 4S4P. “A” is 16 230ah batteries, “B” is 16 100ah batteries, and “C” is also 16 100ah batteries, and “B” and “C” would all be same manufacturer and all made same time (I think, LiTime Trolling Batteries).

Except for occasional balancing, each 4S4P 48 volt bank would always be kept intact (4S4P) for even usage/wear, but the banks may be moved elsewhere to do other things sometimes. But but, especially in summer to run lots of air conditioners at night, all three banks would be at the main house with its a large array or arrays of solar panels. (Let’s say +/- 55 high quality 365 watt panels permanently affixed at the main house. And sometimes a huge cargo trailer with it’s own 8-10 panels on top w/ charger/inverter & batteries inside will be at the main house too. Same goes for a huge 5th wheel trailer. The trailers can contribute AC power to the main house if needed).

Specific question: How to use A, B, and C battery banks “together” at the main house? For safety and long life/health of all the batteries, probably best not to parallel any of the 4S4P battery banks with each other, even not to parallel the identical banks B & C together, is that right? So, how can they all most efficiently work “together” to minimize depth of discharge for all each summer night?

Is the best solution some kind of internal or external automatic battery bank switch/switcher, ie, “A or B or C?” So that when Bank A is discharged to X%, the inverter automatically switches to B until predetermined discharge, then to C?

Or, ugghhh, do I need separate chargers for each battery bank? If I need 3 separate chargers, I guess each battery bank needs a separate solar array? And if so, is it just simpler/cleaner then to have 3 separate inverters too?

The highest priority for this entire plan is ease of use and stability of system. Also being modular and adaptable is high priority.

I have all the new REC panels and 16 new LiTime 230ah batteries so far. I’m strongly leaning towards Victron for almost everything else in light of the recent DIY Solar thread about Victron virtues, but my question is about using multiple battery banks of small batteries with their 4S4P limits. Thank you and Happy New Year!

I think easier to think of each series of four 12V at 48V to be a single battery. And then you are adding a bunch of those batteries in parallel to a power bus of some type.

You can get 48V balancers that connect to each set of four batteries to keep them balanced. To be able to move batteries in 20 lb chunks (Redodo 12V 100Ah mini lfps in my case) is a significant benefit imo. And there are significant savings to be had - four ecoworthy 12V 280Ah or 14kWh of capacity for $520*4. These are heavier than 20lbs but less than a server rack.

 

[Consumerbot3418]

I'm interested in this, as well--I've got 16x 100ah 12V nominal LFP batteries. They were on a 12V Victron split phase, but I've since moved to a 48V inverter, so now they're in 4S4P. I added an active balancer on each 4S string. The cost is significantly lower than, for example, EG4 server rack batteries, and the only DIY required was to wire them in series and add a balancer.

The issue is that all the vendors of these batteries claim to max out at 4S4P config. I'd love to be able to add more capacity, and I'm not really sure I understand why the 4P limit is there. What's the risk of doing a 4S8P setup?

@SupraSPL speculated in another thread "I think the technical reason for limiting how many are in parallel relates to how a fault in one battery or BMS could overwhelm another BMS in the system, potentially leading to an unbelievably powerful short."

My thinking is that too many parallel packs could possibly output more current than the BMS FETs are capable of interrupting, in case of an internal short--and I'd imagine the consequences of that would be catastrophic. I think I'd want to get the batteries out of the garage (maybe build a battery box outdoors) before daring to exceed the 4S4P limit. Then again, that would kinda ruin the value prospect...

 

[sun_of_a...]

My thinking is that too many parallel packs could possibly output more current than the BMS FETs are capable of interrupting, in case of an internal short...

I am a know-nothing novice so I hope others will answer you, but I had a similar question about higher amps and BMSs in the context of exceeding parallel recommendation limit (4) for my new 12V 230Ah LiFePO4s. See thread below.
But in my case, just 12v, no series connection, like you. SupraSPL said to me, "I don't think the extra battery capacity will make it hard for the BMS to balance although you may spend less time in the balance voltage range (above 13.6V)."

https://diysolarforum.com/threads/h...ilt-in-bms-of-12v-lifepo4s-in-parallel.76296/

Best of luck.