MrM1
I'm Here, But I'm Not All There
I had been asking in a different thread I did not start so decided to start my own thread
I have narrowed my new LifePo4 bank size down to either an 8s 272 ah bank OR an 8s2p 564ah bank (8s 272 paralleled). I need 200 amp discharge and so picking a reliable yet affordable permanent install BMS has proven the most difficult part. I have a 2565w solar array of 9 REC 285w panels in 3S3P (95.7 vmp / 89.1 charging amps), 24v Conext SW 4024 24v 4000w inverter, Midnite solar Classic 150 CC and 4 225ah 6v Trojan T105s (too small) for my daily 23hr 3200wh need off grid.
If I go the 8s2p bank, @FilterGuy gave me some interesting things to think about back in this thread.
My 3 biggest concerns:
Here is what I am considering:
Either An 8s 24v 272ah bank with 2 Overkill Solar 24v 100amp BMS system in parallel (I know not recommended but has been done)
Or an 8s2p 24v 564ah bank in this configuration:
Which as I understand from @FilterGuy ... using two 24v 100amp OKS BMS systems would give me 200amp service. As I am seeing things now, this might not be bad. I did list some limitations if one of the two BMS systems shut down 1/2 the bank and I did not know it, but as I understand things right now, the BMS system is actually the 2nd layer of defense and that the Inverter LVC and the CC charge cut off is the primary (?). In other words, the BMS system really should not be shutting things off UNLESS there is a PROBLEM. So it appear this setup would work. Others (@Ampster and @Mac6792 ) listed a few other considerations.
My idea is to order 8 272ah cells now, and test my loads and the system with 2 OKS BMS's in parallel for my loads (I actually might try it with only one BMS and really see if I ever exceed 2400 watts except in surges like well pump startups). ...
BUT then if i discover that an 8s bank of 272ah is just not large enough and I am discharging too much each day (down to 20-25% dod) I would order 8 more cells (say in 6 months) and build up the 8s2p bank.
What am I missing?
I have narrowed my new LifePo4 bank size down to either an 8s 272 ah bank OR an 8s2p 564ah bank (8s 272 paralleled). I need 200 amp discharge and so picking a reliable yet affordable permanent install BMS has proven the most difficult part. I have a 2565w solar array of 9 REC 285w panels in 3S3P (95.7 vmp / 89.1 charging amps), 24v Conext SW 4024 24v 4000w inverter, Midnite solar Classic 150 CC and 4 225ah 6v Trojan T105s (too small) for my daily 23hr 3200wh need off grid.
If I go the 8s2p bank, @FilterGuy gave me some interesting things to think about back in this thread.
My 3 biggest concerns:
- That I have a large enough bank to supply my needs for about a 24hr period at 3200wh per day
- That I have a BMS that can handle a 240v 7amp pump starting up (my inverter can but it can do 4000watts)
- So it would seem I need a BMS that can possibly match my Inverter output although I seldom if ever average more than 2400 watts
Here is what I am considering:
Either An 8s 24v 272ah bank with 2 Overkill Solar 24v 100amp BMS system in parallel (I know not recommended but has been done)
Or an 8s2p 24v 564ah bank in this configuration:
Which as I understand from @FilterGuy ... using two 24v 100amp OKS BMS systems would give me 200amp service. As I am seeing things now, this might not be bad. I did list some limitations if one of the two BMS systems shut down 1/2 the bank and I did not know it, but as I understand things right now, the BMS system is actually the 2nd layer of defense and that the Inverter LVC and the CC charge cut off is the primary (?). In other words, the BMS system really should not be shutting things off UNLESS there is a PROBLEM. So it appear this setup would work. Others (@Ampster and @Mac6792 ) listed a few other considerations.
My idea is to order 8 272ah cells now, and test my loads and the system with 2 OKS BMS's in parallel for my loads (I actually might try it with only one BMS and really see if I ever exceed 2400 watts except in surges like well pump startups). ...
BUT then if i discover that an 8s bank of 272ah is just not large enough and I am discharging too much each day (down to 20-25% dod) I would order 8 more cells (say in 6 months) and build up the 8s2p bank.
What am I missing?
- What problems and limitations am I (in my very novice brain) not seeing?
- Can 8 cells ins series be added for 2 parallel strings in say 6 months later to an LFP bank if needed for extra capacity with out issue?
- Would my existing Array of 2565w 285w panels in 3S3P (95.7 vmp / 89.1 charging amps) be large enough to recharge the 8s2p 564ah bank in a day in NE FL USA? (4.3 average hours of solar sun daily)
- Based on all above, does it just make sense to go ahead and order 16 cells for the 8s2p bank from the start?
Thanks in advance for your help. And thank you for letting me post in this new to me forum.
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