Tell me why I'm wrong, is this even possible?

[solarnoob22]

I think my logic is wrong and I'm overly optimistic. I'm still new to exploring DIY batteries so don't roast me too hard haha.

If I buy individual cells, EVE 3.2 304ah and parallel them, that's 608ah at 3.2v?
If I do series this combination 8(?) times to reach 24v that's 15,564kwh? (25.6x608ah?)
Would the BMS connect to each individual 608ah 3.2v pair and act accordingly?

I'm sure this has all been asked before, as I haven't seen too many large kwh battery builds, I'm sure there's lots of hurdles I'm unaware of.

 

[upnorthandpersonal]

Yes.

However I prefer to monitor each cell separately instead of parallel cells (and parallel the batteries instead). It adds redundancy, and you don't have to take everything down to do maintenance on one of the packs.

 

[solarnoob22]

Yes.

However I prefer to monitor each cell separately instead of parallel cells (and parallel the batteries instead). It adds redundancy, and you don't have to take everything down to do maintenance on one of the packs.

So this is all incorrect or is it all possible?

 

[upnorthandpersonal]

All correct.

 

[sollap]

In case it wasn't clear, what upnorthandpersonal was recommending is that you build 2 separate 24v/304Ah batteries and parallel those batteries. This requires a second BMS, but it's better than a single 16 cell 24v battery because each individual cell can be separately monitored, balanced, etc. It also allows you to keep your system running on one battery while you work on the other. Your total available AmpHours are the same either way.

 

[MisterSandals]

If I buy individual cells, EVE 3.2 304ah and parallel them, that's 608ah at 3.2v?
If I do series this combination 8(?) times to reach 24v that's 15,564kwh? (25.6x608ah?)

Thats 16 cells x 304Ah x 3.2V nominal = 15,564Wh not kWh

 

[MisterSandals]

If I do series this combination 8(?) times to reach 24v

And, its important to create pairs as equal as possible in capacity to the other pairs.

The rough way would be to pair the strongest cell (highest capacity) with the weakest cell (lowest capacity). Second strongest with second weakest. This strongest with third weakest.

This will give you the best chance at creating a battery that charges in a balanced manner.

 

[upnorthandpersonal]

15,564Wh not kWh

Yeah, we use a ',' to indicate decimals here, so I didn't catch that - but I guess OP knew he wasn't getting 15MWh

 

[fnnwizard]

I think my logic is wrong and I'm overly optimistic. I'm still new to exploring DIY batteries so don't roast me too hard haha.

If I buy individual cells, EVE 3.2 304ah and parallel them, that's 608ah at 3.2v?
If I do series this combination 8(?) times to reach 24v that's 15,564kwh? (25.6x608ah?)
Would the BMS connect to each individual 608ah 3.2v pair and act accordingly?

I'm sure this has all been asked before, as I haven't seen too many large kwh battery builds, I'm sure there's lots of hurdles I'm unaware of.

Doing it your way will require just 1 BMS with caveats:
The balancing resistor will work 2x as hard to keep balance a 608Ah "cell"
you'll have to match the pairs according which means you have to cycle each 1 cell = takes a lot of time.
The connection with each 2P "cell" will be negative of 1 cell and positive of other cell to the next 2P "cell".

With current manufacturing tolerances, if A grade cells, 2P is not a problem if matched first. The weakest 2Pcell in the whole group is what your total pack will be.

Doing it per upnorth would require 2 BMS, but should be better as you get individual cell data and does offer battery level redundancy as well as 2X balancing (same current into 2x bigger cell vs 1p cell) when needed.

 

[time2roll]

I have two 12v batteries configured with pairs of cells to increase capacity. No issues.

Yes 3.2v x 304 ah x 16 = 15.564 kWh. No matter which way they are connected.

 

[solarnoob22]

Thanks everyone for the answers. So ill build two 8s and parallel them together with two separate BMS's. Is there a consensus on the better quality BMS manufacturers? I have an LV2424 that can output around 30 amps, and I believe can charge at 140 amps with utility and solar combined.

 

[MisterSandals]

So ill build two 8s and parallel them together with two separate BMS's.

If you can, put the strongest 8 cells in one battery and the 8 weakest in the other.

It is helpful to have cells of similar capacities in each battery.

 

[robbob2112]

If you can, put the strongest 8 cells in one battery and the 8 weakest in the other.

It is helpful to have cells of similar capacities in each battery.

Order the batteries by internal resistance? Max voltage? What?

 

[fnnwizard]

Thanks everyone for the answers. So ill build two 8s and parallel them together with two separate BMS's. Is there a consensus on the better quality BMS manufacturers? I have an LV2424 that can output around 30 amps, and I believe can charge at 140 amps with utility and solar combined.

for 8S, I find Jk's ( be sure to get the "smart ones) a bit better due to more consistent shunt readings and more parameter config/displays.

Order the batteries by internal resistance? Max voltage? What?

I'm pretty this means actual capacity Ahr,Whr, so would need to cycle them.
What the diy sellers say are grade A cells will typically be 5-10% over rated capacity and should each be within 1% of each other.

 

[MisterSandals]

Order the batteries by internal resistance? Max voltage? What?

Sorry I was not specific! Group highest capacity cells in one battery and lowest in the other.