Anyone mix 280K with 280-non-K cells in a 48v pack?

[Steve_S]

I dunno about suppliers in USA, gotta take your chances searching Amazon/EBay etc...
I'm in Canada and get "some" materials from here, few things from the US but mostly direct from China and when small/light enough by Airfreight express if I need it fast.

 

[GuyG]

You don’t really need it.

When your new cells arrive, measure the voltages. Then use your inverter to charge (or discharge) your existing battery so that the newer cells in it are at least in the neighborhood of the cells you’re buying. Then swap out the old cells from your battery for the new cells you just bought. Let your charge controller/inverter get the battery charged, and let the JK do its active balancing thing. Should be fine.

 

[OffGridIdaho]

You don’t really need it.

When your new cells arrive, measure the voltages. Then use your inverter to charge (or discharge) your existing battery so that the newer cells in it are at least in the neighborhood of the cells you’re buying. Then swap out the old cells from your battery for the new cells you just bought. Let your charge controller/inverter get the battery charged, and let the JK do its active balancing thing. Should be fine.

Rodger that. I will give it a try. If I can find a usa charger I guess its always good to have one just in case. Or if I upgrade again to 2p=1s 48v

Its a shame SS sent me a New Old Stock older serial number Multiplus 2 with a bad motherboard (25Hz PWM fan rattle). Now I have to deal with a second problem.

 

[OffGridIdaho]

Well, found usa stock just in case anyone else needs one.

https://www.docanpower.com/index.php?route=product/product&product_id=550

 

[GuyG]

That’s a good price. But be aware that item is NOT designed as a charger. It’s designed to test individual cells. Sure, it will charge one prismatic cell at a time, but since it tops out at 5 volts it will NOT charge even a six-volt pack much less a 48-volt.

 

[Steve_S]

Well, found usa stock just in case anyone else needs one.

https://www.docanpower.com/index.php?route=product/product&product_id=550

OK, a LOT of folks here use THAT EBC 40 & EBC 20 for testing & TOP Charging Balancing sets and have done so since they came to market about 3 years ago or so.

Top Charging cells means taking 1, 4, 8 or even 16 cells in Parallel up to 3.650V MAX !
That EBC is NOT intended to charge a 12V/24V or 48V pack.

PARALLEL: Meaning connect the Cells are all connected + to + to + and - to - to -

 

[OffGridIdaho]

OK, a LOT of folks here use THAT EBC 40 & EBC 20 for testing & TOP Charging Balancing sets and have done so since they came to market about 3 years ago or so.

Top Charging cells means taking 1, 4, 8 or even 16 cells in Parallel up to 3.650V MAX !
That EBC is NOT intended to charge a 12V/24V or 48V pack.

PARALLEL: Meaning connect the Cells are all connected + to + to + and - to - to -

I was just about to say that.

I am watching my cells as they charge at 15a-solar this am. They were balanced to .010 until 3.35v and then they started drifting. The new cells are climbing away in voltage. v2=3.35 and v3=3.45 .116 delta now and it will go higher until it hits parameters.

 

[Steve_S]

I just drew this up quickly to help. Pictures are so much simpler eh.

 

[740GLE]

With a JK BMS and 2 amp balancing Id let it charge up how ever your charging it and keep any eye on the cells over a couple weeks or so.

 

[OffGridIdaho]

I just drew this up quickly to help. Pictures are so much simpler eh.

View attachment 226293

OK thanks,
What is your mppt charger set to for 48v?

Absorb
Float
re-bulk offset
absorb duration (adaptive or fixed)
Maximum absorb time
Max charge current

 

[Steve_S]

I run 24V.
Here's something in one of my threads that I give out all the time. It's "Moderate" profiles that work pretty well for most everyone who uses them.

SETTING	V per cell	12V	24V	48V	notes
Bulk / Absorb: (boost)	3.437	13.74	27.5	55.0	Absorb < 60min Transitions to Float
Equalize:	0				NOT for Lithium Based Batteries
Float	3.425	13.70	27.4	54.8	allows cells to balance internally
Min Volts:	2.650	10.6	21.2	42.4	Never allow to drop too low. Safe Buffer
Max Volts:	3.575	14.3	28.6	57.2
Rebulk Voltage:	3.200	12.8	25.6	51.2
End Amps / Tail-Current:					formula: 100AH X 0.05 = 5A

(*1): End Amps is calculated: (100AH X 0.05 = 5A or 280AH X 0.05 = 14A.
EndAmps = TailCurrent
Coulumbic Efficiency / Battery Status Meter Efficiency for LFP = 99%.
This gets the bank charged to full with high amps (Constant Current Constant Voltage) and then float (Constant Voltage, Variable Current) tops off so the cells are at 3.437Vpc. I
! Do Not forget to adjust for Voltage Offsets between Actual Voltage @ Battery Terminal & at Solar Controller.

BMS With Active Balancing should be set to start Active Balancing at 3.420V or possibly lower to 3.410 so that the cells can balance out at the top and not affect the charging process.

 

[OffGridIdaho]

OK so more info......

I carefully watched the batteries when it was charging. I think I know why things got so out of balance. After 4 days they were balanced in the AM. So I watched them charge the whole morning. I lowered the mppt incoming amps to 12a. I watched what the V3 and V2 did during charge. They held fairly close during the first part. Got a tiny bit out during second part (.010). Then all of the sudden the old pack just shot to the roof.

I think the old pack was full and the V shot up like a full battery. The new pack stayed low as it was still charging. So today I lowered my absorb and float settings by 1v. It went smoothly until the end and then the old pack climbed. I lowered the V by another .3 and that seemed to stabilize the pack.

So the old pack is just filling up before the new. Well, the new batteries will solve that issue.

Cell delta in the AM before sun hit panels was .003..