DIY EVE/Lishen Battery

[gmflash88]

I'm thinking of going down the DIY battery path but can't find solid information whether or not I can parallel two completed batteries. I'd like to series connect 4, 280ah cells and then parallel two sets for a total of 560ah capacity.

I ask the question because it seems to me that I had read somewhere that those cells don't "like" being connected that way.

Assuming that's fine, would I connect a BMS to each group or one BMS to the whole array?

Thanks!

[s2mikon]

So you want a 560 amp hour 12 volt battery pack? I think it would be better to parallel 2 cell packs 560 amp hour 3 volt and series those to get to 560ah / 12v pack. 24 v 580 ah would be better. Then there is the question of how many amps do you want to pull and length of cable and over current protection. Did I miss something?

[gmflash88]

Originally Posted by s2mikon

So you want a 560 amp hour 12 volt battery pack? I think it would be better to parallel 2 cell packs 560 amp hour 3 volt and series those to get to 560ah / 12v pack. 24 v 580 ah would be better. Then there is the question of how many amps do you want to pull and length of cable and over current protection. Did I miss something?

I was thinking that I'd get 8 of the 3.2v cells and creating 2, 12v batteries that are 280ah each and then parallel those for 560ah.

As far as 24v...I have no idea. If I open that up I'm sure that'll just be another whole rabbit hole for me to go down.

[s2mikon]

I am of the understanding that these things don't like to be paralleled due to charging level balance. Is there an over riding reason that you can't use 24 volt? 24 volt does make cable sizing smaller with less losses. The biggest question I have is how many amps will you be pulling? What are you trying to run with this?

[gmflash88]

Originally Posted by s2mikon

I am of the understanding that these things don't like to be paralleled due to charging level balance. Is there an over riding reason that you can't use 24 volt? 24 volt does make cable sizing smaller with less losses. The biggest question I have is how many amps will you be pulling? What are you trying to run with this?

Going to feed into an inverter charger then out to the refrigerator. Of course there will be other items, but the fridge would be the only 110v item. Everything else will be 12v (lights, charging ports, water pump, igniter for wh, etc). I'll have a few 110 fed outlets, but nothing that is permanently connected to them.

I suppose I could series all 8 for a 24v, 280ah battery. At the end of the day, I think I'd be accomplishing the same thing which is ultimately just ensuring a longer run time on the fridge.

[BeNimble]

generally it is best to parallel at the cell level, you only have to monitor 4 voltage levels,
the cells 'self-balance'. Inside big ones they are often just parallel cells.

Make two 12v strings would allow you to get 24 volts if needed, and make it easier to add more capacity vs cell level, and could take one string offline and not cut all power, but this isn't usually done, so I'll probably be doing it since many say don't do it, it won't work, you will die, catch fire, kill children, etc.

[john61ct]

It is sub-optimal for sure.

Better to parallel at the 1S level first, then connect in series so you only have one string.

What is your motivation for serial'ing first?

[gmflash88]

Originally Posted by john61ct

It is sub-optimal for sure.

Better to parallel at the 1S level first, then connect in series so you only have one string.

What is your motivation for serial'ing first?

I guess I don't follow. Am I wrong that the 4, 3.2v/280ah cells need to be connected in series to "create" a 12v/280ah battery?

My initial question was can I not create 2 of these 4 cell batteries and then connect those 2 (parallel) to create a 12v/560ah bank vs an 8 cell, 24v/280ah bank?

[joeblack5]

No you are right and you can do that. John is suggesting you connect 2 cells in parallel to create one block of 3.2 volt at 560 ah and then putting 4 of those assembles in series to get to your 12 volt.
The main reason would be that you only need a 4 cell bms.

I have three individual string the way you describe it . Each string has its own bms. And has its own shunt and fuse. I wanted to avoid other cells to discharge over a broken internal shorted cell without fuses being in between.

All have there pro and cons.

Johan

[turf]

i went down that path.

i only got 4 of the cells to make a 12v battery. i made it as a replacement for my 12v battery bank. it runs a 12v house system, no inverter.

if you throw an inverter and a lot bigger loads, the amp/wire size gets stupid @ 12v with that capacity.

if i add an inverter, i will change my system to a 24v.

my caveat about the diy path is the build quality. if i were in an accident, who knows what that battery would do.

[rffffffff]

Originally Posted by turf

i went down that path.

i only got 4 of the cells to make a 12v battery. i made it as a replacement for my 12v battery bank. it runs a 12v house system, no inverter.

if you throw an inverter and a lot bigger loads, the amp/wire size gets stupid @ 12v with that capacity.

if i add an inverter, i will change my system to a 24v.

my caveat about the diy path is the build quality. if i were in an accident, who knows what that battery would do.

wire size is one part and solar charge controllers are another. you can get away with half as much charge controller for a 24v system vs a 12v system.

if it wasn't clear in the above posts, you can make a 12v 560ah battery as you describe but its in the details.. you have to make four 3.2v 560ah batteries by paralleling two cells, then connect those cells in series to make your battery as opposed to making 2 12v batteries and then paralleling them. It's just the wiring configuration that's different, not a big deal.

that all said, 24v is far better in almost every way. I regret buying 12v components when I started but I just though that was what you were supposed to do.

[peterbylt]

I am in the process of building out my Solar system now.

I currently have just a 12 volt 8D Lead acid Battery and a charger that powers the LED lights and the water pump, looking to greatly improve on this setup.

Wanting to have a better capability when Boondocking.

115 volt AC loads, I would like to be able to run the Refrigerator 6.5A all the time, the Mini Split AC 6.8A some of the time, TV some of the time, Microwave on occasion, charge phones.

12 volt loads would be LED lights (unknown amps) and water pump 7.5A intermittently.

I have started purchasing some of this stuff.

I already have the Solar panels and the Inverter/charger, within the next few weeks I will be ordering the Batteries, they say it takes up to 2 months to get the batteries from China.

I will order the Electrodacus equipment about the same time.

I really like the concept of the Electrodacus Equipment.

https://electrodacus.com/

24 volts looks to be the way to go, I was able to acquire an Aims 24 volt 3000 wat inverter/charger at a really good price.

The current plans call for 8 280ah Lifepo4 cells setup as a 24 volt battery.
This is my current design.



Peter

[john61ct]

Better if we keep our different build threads separate

[john61ct]

Cells in parallel are called a group, in that case 2P groups, 2P1S,

but the 1S does not need to be stated, implied if left out.

Cells in series, or groups in series, are called a string.

OP was talking 4S2P, putting two 4S (12V) strings in parallel.

I stated that 2P4S is better, putting 4x 2P groups in series (at 1S voltage), so there is just one string.

Only one BMS, and no imbalance issues that you get from paralleling multiple strings (at the bank-level voltage)

You should have gear % know-how to periodically cap test your cells, anticipate any issues no surprises, better to not need fuses withing your House bank, not just higher overall capacity but greater simplicity means higher reliability, reduce possible points of failure, only have one bank to monitor.

_______
There are **some** advantages to going to 24V or 48V for that matter

but only in some use cases, and you may end up needing 12V circuits anyway, and DCDC conversion adds costs and complexity, so I reco going higher on the whole system only if you know you have compelling reasons.

_______
For living off grid, mostly solar inputs, inverters should be avoided as much as possible, the appliances designed to run on American grid AC power are usually **very** inefficient.

[john61ct]

Originally Posted by gmflash88

I guess I don't follow. Am I wrong that the 4, 3.2v/280ah cells need to be connected in series to "create" a 12v/280ah battery?



My initial question was can I not create 2 of these 4 cell batteries and then connect those 2 (parallel) to create a 12v/560ah bank vs an 8 cell, 24v/280ah bank?

You can, but again, many reasons not to.

Double up your cells at the 1S level, in effect each 560Ah group becomes a bigger 3.2V cell.

Then those groups (pairs in this case) get connected in series to get to 2P4S, a single string at "12V nominal" to create your 560Ah House bank.