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

[sun_of_a...]

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!

 

[zanydroid]

What do you mean by 4s4p? 48v usually means 16s in LFP. As such your post is pretty confusing

16s @ 100ah already exceeds what I would consider mobile/portable in mass. Unless you are breaking the pack into modules that you move individually.

 

[timselectric]

I believe they are talking about 12v batteries in series.
Not recommended at all.
I'll just say, good luck.

 

[Dagoth Ur Does Solar]

I could be wrong about this, but I think most people who run multiple, totally separate battery banks end up simply doing DC to DC charging between the banks? At least, I've seen many people do this when they have, say, a bank of older AGM batteries hooked up to a system and want to expand by adding some LFP batteries.

Also, rather than going with a 4S4P setup with the 230Ah packs, is there a reason you didn't consider just going with a 48V rack setup? I would think the way to have less "togetherness" is to buy less batteries- just get bigger ones.

What do you mean by 4s4p? 48v usually means 16s in LFP. As such your post is pretty confusing

16s @ 100ah already exceeds what I would consider mobile/portable in mass. Unless you are breaking the pack into modules that you move individually.

Fairly certain he is referring to LiTime's 230Ah 12v batteries (I have one). They claim the max their BMS supports is having 4S4P- thus, 16 batteries totaling 48V. Someone smarter than me can correct me, but I'm pretty sure they're just making that up- to my knowledge there's no way the individual BMS have any idea how many batteries are paralleled. I would guess it's just to prevent people from paralleling a ton of them and having a bunch of SoC imbalances across the bank.

 

[sun_of_a...]

What do you mean by 4s4p? 48v usually means 16s in LFP. As such your post is pretty confusing

16s @ 100ah already exceeds what I would consider mobile/portable in mass. Unless you are breaking the pack into modules that you move individually.

All these smaller LFP batteries say a 48 volt battery bank size is maxed out at 16 batteries: 4 in series x 4, the strings are paralleled. Jeez, have I got that wrong!

Yes, sixteen 12 volt batteries to a battery bank.

 

[sun_of_a...]

I believe they are talking about 12v batteries in series.
Not recommended at all.
I'll just say, good luck.

Could you say more? It's okay, if I F'd up buying those batteries, oh well, break it to me please.

 

[sun_of_a...]

IAlso, rather than going with a 4S4P setup with the 230Ah packs, is there a reason you didn't consider just going with a 48V rack setup?

Cost of batteries. Weight. Modularity.

 

[sun_of_a...]

Thanks for the reply. Regarding

I could be wrong about this, but I think most people who run multiple, totally separate battery banks end up simply doing DC to DC charging between the banks? At least, I've seen many people do this when they have, say, a bank of older AGM batteries hooked up to a system and want to expand by adding some LFP batteries.

Thanks for the reply Dagoth. I wonder if this is safe or good for batteries?

 

[Dooug]

The 4s part is the biggest problem, you'll need a balancer test keep all 4 the same voltage.
The cheaper batteries already struggle to balance internally and it just takes one runner cell to kick a 12v out and you lose your 4s function.

With 1 bms running 16 230 ah cells you only have one brain running the show instead of 4 that don't talk to each other.

I'll be running 24 volts with 2s aolithium batteries temporarily, have purchased a balancer to keep things in check. I'm not happy about it, but need power and not ready to order a pallet of cells for the camper and off-grid house.

 

[Dagoth Ur Does Solar]

Thanks for the reply. Regarding

Thanks for the reply Dagoth. I wonder if this is safe or good for batteries?

It's not something I've done and someone more knowledgeable would have to give you some input- it's much more commonly used when people want to transfer energy between two banks of different voltages.

There are threads here asking about what you'd like to do, but it looks like most people just ended up giving up on trying to do it.

 

[sun_of_a...]

The 4s part is the biggest problem, you'll need a balancer test keep all 4 the same voltage.
The cheaper batteries already struggle to balance internally and it just takes one runner cell to kick a 12v out and you lose your 4s function.

With 1 bms running 16 230 ah cells you only have one brain running the show instead of 4 that don't talk to each other.

I'll be running 24 volts with 2s aolithium batteries temporarily, have purchased a balancer to keep things in check. I'm not happy about it, but need power and not ready to order a pallet of cells for the camper and off-grid house.

Thanks Dooug, really. So I should go with 48 volt batteries, that is each battery is 48 volt? I can use these others for the trailers. I wanted the trailers to be 48 v systems, but I could do 24v systems in them. Is 24volt ( ie 2s 12v batts) less problematic to balance than 4s? How many 48v of these 230ah batteries can go to a bank, and how wired together? Thanks.

 

[sun_of_a...]

There are threads here asking about what you'd like to do, but it looks like most people just ended up giving up on trying to do it.

And they do what instead? for really big battery banks, they just buy huge 48v batteries and wire them in parallel? Thanks.

edit: it makes it hard to put on yachts. So maybe that's what these batts I already got will be for. My research so far says that for rough water multiple 100 or 200 ah batteries are what you want cause the big one fail soon under the stress.

 

[zanydroid]

They claim the max their BMS supports is having 4S4P- thus, 16 batteries totaling 48V.

That’s still 12V

 

[sun_of_a...]

That’s still 12V

Cryptic. I kinda feel like I'm in the twilight zone, what little I thought I was starting to learn about this stuff seems to be evaporating... Is this stuff knowable?

 

[zanydroid]

4s = 4 in series

4p = 4 in parallel

Reading from right to left corresponds to inside to out in the schematic.

Either way 4p4s and 4s4p , while wired differently, totals to 12v

 

[zanydroid]

Exchanging power between batteries using a charger is the safest way to do it. I don’t think people are regularly connecting batteries in parallel since there’s little reason they would be close enough in voltage to avoid a very high current when they connect.

You can lookup some EV build videos or general battery build videos to see how careful people are with this, when working with batteries with as much power output potential as lithium.

 

[Dooug]

4s = 4 in series

4p = 4 in parallel

Reading from right to left corresponds to inside to out in the schematic.

Either way 4p4s and 4s4p , while wired differently, totals to 12v

If using 4 3.2v cells then yes 12v. I believe the original comment are around using 12v battery assemblies in 4s4p for 48v total.

With proper bus bars and cabling you should be able to stack many 48v batteries in parallel. SOK has a rack for ten...really it's the bus Bars that would limit paralleling. Not sure why the 12v Lithiums max out at 4 parallel, maybe they assume the batteries are directly wired, terminal to terminal rather than battery to bus Bar, with equal length cables.

 

[zanydroid]

I don’t know why LiTime wants to call it 4p4s instead of 4p4s4s

 

[sun_of_a...]

So, my original question about being using multiple battery banks with some kind of automatic battery bank selector/switcher which switches automatically to another bank as the current bank gets discharged to a certain level went unaddressed for two reasons maybe. 1. Wiring 4 12v lithiums in series to get 48 volts seems to be a bad idea cause it's a balancing nightmare, and dangerous? Would a battery balancer or a single BMS for these 16 230ah LiTime12v batteries allow them to be properly wired in series and parallel 48v (4p4s4s)??? Or is the problem inherent? Is the balancing problem reduced by half by going to a 24v system? And eliminated if I stick with a 12v system for these 12v batteries?

2. connecting one battery bank to another appears to be bad idea. So, again, the automatic switcher?

So, the answer is to just have one battery bank w/ real 48 v batteries and wire as many as you want in parallel using proper wiring and bus bars, that's the answer? No batteries in series?

edited

Thank you Zany and everyone for the help.

 

[zanydroid]

I think the original post was a little too long and hard to parse.

Why would you do automatic battery bank switching vs permanently wiring parallel banks in place? You do need some mechanism to allow you to safely swap parallel banks in and out, and you need some scheme to deal with non-matching voltages while switching. If you parallel two banks together - nonmatching voltage, high current. If you switch out a bank, and then another one, not letting them touch, there will be non-matching voltage between the input capacitors on the inverter and the new battery bank. Perhaps you could rig up a multi-position switch so that you always proceed through a precharge resistor + some kind of current meter, and only proceed past the precharge position once the voltages have converged.

Where would you put the fuses/breakers with all this switching?

If you stick with 12V there is no balancing issue. The internal balancer on the 4s BMS will take care of it. If you go to 24V, the amount of time you can get away with not balancing goes up, since the combinatorics are more favorable (you need at least one 12V to be out of balance relative to the rest for there to be capacity loss, and if you work out the math the more you have in series the higher the probability)

When you commission a battery bank, you need to balance (either top or bottom) to bring them to the same voltage, after which you can connect without a burst of current. When you permanently stick parallel battery banks together, they should from that point onward be self balancing provided there are no problems with the wiring causing asymmetric discharge / charging.