Upgrading from FLA to LifePO4

[bluefin99]

Currently charging a 24v lead acid setup ( 4ea 6V 200 ah wired in series ) from a Renogy Rover 100 amp CC. Will be switching to a 24V LifePO4 set up ( 2 ea. 12v 280 aH ) and wondering if I need to make setting adjustments before connecting CC back to solar again.
according to the dealer, i only need to change two settings:
Bulk 28.8v
Float 27.v
But also read that recommended to disconnect battery temp moniter ( not sure why..)? Is there a place I can determine exactly what I need to adjust for these new batteries ? Renogy isnt exactly easy to get a hold of..

On a related note, I also need to modify my Schneider Conext SW4024 inverter so any guidance there would be helpful.
thx

 

[BentleyJ]

You would be much better off with a single 24V battery. LFP is different than LA. Requires a BMS and cell balancing. With 2 batteries, the BMS will only be connected to 4 cells not all 8. There are balancer modules that can help with separate batteries in parallel but its unnecessary extra equipment.

 

[chrisski]

Will be switching to a 24V LifePO4 set up ( 2 ea. 12v 280 aH ) and wondering if I need to make setting adjustments before connecting CC back to solar again.

I have 280 ah cells in my RV I made a battery out of and was super frustrated that there was no source that told me how to charge. I will tell you what I do #1, and give you to a link for the other batteries I use for my house #3for that has a link for a Schneider inverter. Between that and the data sheet from the cells, along with free advice, you need to choose something. #2 is just more free advice.

1) For 280 ah cells, I charge at 3.475 absorb/bulk. Float I lower that so that the sun still powers my loads, ie, if I have 300 watts of panels and my SCC is pushing 50 watts in the sun, time to up the float voltage.

Bulk/Aborb 27.8.

IMO 28.8 at 3,6 per cell is too high for bulk so if cells are unbalanced could lead to a BMS trip or runaway cell.

2) 2 X 12 volt lithium in series is NOT accepted practice. They can "unbalance from each other." A Battery balancer will prevent this. Sometimes you can't assemble as a single battery. There are threads that show how lithium batteries in series unbalance.

3) This is an Inverter Guide that tells settings for the batteries I use in my house. This has a link for Schneider. Section 4 talks of 48 volt settings, so you could halve those. THere is four sets of settings:

 

[fratermus]

Renogy isnt exactly easy to get a hold of..

Luckily the documentation stays online 24/7.

also read that recommended to disconnect battery temp moniter ( not sure why..)?

Controllers charging lead chemistries use temp to "compensate" (adjust) the actual charging voltage: colder lead needs higher voltage, warmer needs less. Li does not need/want that. If you are using an Li profile it is likely that the controller is not using temp compensation at all. But you can "belt and suspenders" it by setting the compensation to zero. (pg 23 of the manual)

Edited to add: the spec sheet says "0mV / ℃ / 2V; no compensation (Lithium)"

HOWEVER, some Renogy controllers {in Li profiles} use the temp probe to stop charging when the battery is very cold. Dunno if yours does or not. It might be worth testing by using a Li profile and freezing teh temp probe, similar to what Will has demo'ed in most battery teardowns.

If you do test please report back with the firmware version and what you find.

 

[alcook62]

On a related note, I also need to modify my Schneider Conext SW4024 inverter so any guidance there would be helpful.
thx

I have that particular inverter and switched to LiFePO4 three years ago. You can implement a custom battery profile by accessing the "advanced settings" menu and go to "charger settings" and select "custom". From there you can set the parameters you feel are best.