24V BYD powerwall

[Jerryonthego]

Hi all! New to solar and took a dive in. Have a 700 array 2S2P and an MPP 2424LV setup. Wanted a somewhat simple first setup for solar. My first BYD peer walk was defective and Bigbattery sent a replacement without issue. Was a pain to ship the defective unit back... these things are heavy . Anyway, I can’t seem to charge the unit higher than 26.7 volts. Is that to be expected? I know these are used... but in growing this forums posts in these units.... it seems that 28 volts is the norm to be expected. Any thoughts?
Also what should the low voltage disconnect be set at. Is 23v too low? Would 24v be ideal. Would appreciate some guidance. Thanks in advance. I added a pic of my setup for some thoughts off I am doing something incorrect.

 

[nosys70]

a LFP is standard at 3.2 , so 26.7/8 = 3.3375. that is pretty a 100% SOC value.
the discharge curve is pretty flat, so you should have all the power available between 3.33 and 3.0
you can just make a test, charge to 27, , put a 250W load on an inverter and let it go.
the time will help you calculate how much you get from the battery.
if it is a 2nd hand battery, it is better not to discharge under 2.9 and not to charge over 3.3, except if you are balancing.
My new Xuba 280Ah battery are giving me 90% of power between 3.3 and 3.0
that is the way LFP works. If you use lithium, then the voltage span is a lot higher, you have a 100% SOC at 4.12V and 0% can go deep to at 3.0V

 

[Mtour]

My experience with these used byd's is not to charge them over 27v. I charge mine to 27.2v in bulk and then float at 27v all day. These voltages have been for me, set it and forget it...
Takes about 3-7hrs on float to reach 96% charged. I have charged individual cells after the extended float and they only take additional 4-8amps to get to 3.65v. After 8hrs on 27v no cell is over 3.42v.
I have tried many different bulk voltages over 3.36v per cell and they always end up with a runner, given time. The time at absorbtion voltage over 3.36v to get a runner is dependent on the depth of discharge.

These days I am using 15% of my bank nightly, on float by 10am.. I have been running these voltage for four month now and the byd's have been very stable.. I have the back to grid voltage set at 49v, cells are 20-40mv pretty much the whole time....

 

[Jerryonthego]

Thanks for the insight and feedback. Very helpful!
Still learning

 

[GVSolar]

I have 4 of the the 24v Techdirect/BigBattery pre-assembled units - I rate them at 3kwh per unit. They are wired in parallel to an Schneider Conext SW4024 system and three solar arrays totaling 4.5kw. The units have been in operation continuously for about 4 months - and are operating flawlessly. Totally off-grid. I use conservative charging specs - 27.2 bulk, 26.7 float, 26.4 bulk recharge reset, and have significant loads. One thought: From your photograph, it occurs to me that you might be using so little of the battery's capacity (recharging tools only) that the battery is reading full (based on charger reading minimal charge amperage), or the BMS is cutting out because of one runaway cell. Just a thought. Best.