Lifepo4 charge discrepancy.

[Pickuptrck]

Hello. Relatively new to The forum but not necessarily new to solar, just LFP batteries. I've gone through many of Will's YouTube videos, and I found a few disparities on recommended charging profiles and wanted to set the record straight.

YouTube MPP inverter video 1:
C4 (bulk) 58v
Fl4 (float) 57v
Big battery modules (possibly li-ion??)

YouTube MPP inverter video 2:
C4 (bulk) 56.4v
Fl4 (float) 55v
Battleborn modules

Which is right? Both appear to be using lfp batteries and inverters from the same company, though different models.

My main concern is with about 30-50a avg typical of charge, at night my battery resting voltage is around 52.5 to 53.2. The inverter has shut off a couple of times (48v) with an extremely small load of some RV lights and an RV fridge. I would like to boost the power and have intentions on tripling the battery size from 13 kW to close to 40 when the house is built later this year

My system:
16s 280ah raw cells /13kw
Dally BMS 200a charge 100a load, non-bluetooth
MPP LV6048
3s3p 355w JA solar in PV1 about 5yrs old
3s4p 260w REC into PV2 about 7yrs old
Fully off-grid.

Future plans (about 8 months)
20kw of 400w panels, full swap of current panels
26kw more battery
additional LV6048 in parallel/12kw total
240v 9kw backup generator

Full house load calc may change some of the above, working on picking appliances in March.

 

[sunshine_eggo]

Hello. Relatively new to The forum but not necessarily new to solar, just LFP batteries. I've gone through many of Will's YouTube videos, and I found a few disparities on recommended charging profiles and wanted to set the record straight.

YouTube MPP inverter video 1:
C4 (bulk) 58v
Fl4 (float) 57v
Big battery modules (possibly li-ion??)

YouTube MPP inverter video 2:
C4 (bulk) 56.4v
Fl4 (float) 55v
Battleborn modules

Which is right? Both appear to be using lfp batteries and inverters from the same company, though different models.

My main concern is with about 30-50a avg typical of charge, at night my battery resting voltage is around 52.5 to 53.2. The inverter has shut off a couple of times (48v) with an extremely small load of some RV lights and an RV fridge. I would like to boost the power and have intentions on tripling the battery size from 13 kW to close to 40 when the house is built later this year

My system:
16s 280ah raw cells /13kw
Dally BMS 200a charge 100a load, non-bluetooth
MPP LV6048
3s3p 355w JA solar in PV1 about 5yrs old
3s4p 260w REC into PV2 about 7yrs old
Fully off-grid.

Future plans (about 8 months)
20kw of 400w panels, full swap of current panels
26kw more battery
additional LV6048 in parallel/12kw total
240v 9kw backup generator

Full house load calc may change some of the above, working on picking appliances in March.

For fast charging (generator):
56.8 Absorption (3.55V/cell)
54.4 Float (3.4V/cell)

For slow charging with a long absorption time and potential increased cycle life (solar/grid):
55.2V Absorption (3.45V/cell)
54.4 Float

 

[Pickuptrck]

Thank you. I thought 57v and 58v seemed unreasonably high. Maybe the Big Battery units function better bouncing off the limiter or internally defuel the voltage?

 

[sunshine_eggo]

Thank you. I thought 57v and 58v seemed unreasonably high. Maybe the Big Battery units function better bouncing off the limiter or internally defuel the voltage?

IMHO, Big Battery has their head up their butts. They make recommendations based on LFP generalizations rather than what is best for the cells they use and what is sensible for the end user.

 

[Pickuptrck]

Gottcha, thanks for the info. I'm having a ?BMS? Battery imbalance issue, I'll post it separately tomorrow with some specs. Im regretting not checking the BMS was smart to make the battery easier to monitor.. live and learn.

 

[sunshine_eggo]

Gottcha, thanks for the info. I'm having a ?BMS? Battery imbalance issue, I'll post it separately tomorrow with some specs. Im regretting not checking the BMS was smart to make the battery easier to monitor.. live and learn.

Not uncommon with Big Battery units. The slow charging settings I mentioned above may help restore balance sooner and help you avoid high voltage disconnects.