Should Schneider System be AC or DC Coupled w Lithium Batteries?

[Trygves]

I have a Schneider system consisting of XW+6848, MPPT 80 600, 48 Volt Lithium Batteries. The system allows AC Coupled or DC Coupled and I wonder which of the 2 choices I should use. Schneider has Solution Guide 976-0240-01-01 Rev D which tells me that if I use Lithium batteries I should have a DC Coupled system and I have had it as a AC Coupled system now. Any thoughts from wise men out there using a similar system.

 

[ElectricIslander]

DC coupling is far more common and is a simple solution for off-grid use with batteries.

 

[BentleyJ]

I have a Schneider system consisting of XW+6848, MPPT 80 600, 48 Volt Lithium Batteries. The system allows AC Coupled or DC Coupled and I wonder which of the 2 choices I should use. Schneider has Solution Guide 976-0240-01-01 Rev D which tells me that if I use Lithium batteries I should have a DC Coupled system and I have had it as a AC Coupled system now. Any thoughts from wise men out there using a similar system.

You recently had a fairly lengthy thread regarding a Xanbus communication problem with your 2 charge controllers which seems to have been resolved. So we know your system is DC coupled and apparently AC coupled as well? I'm guessing with an existing grid-tied system. At least this is the most common way most of us end up with AC coupling because we wanted to add battery back up and/or Peak Load Shaving to an existing grid-tie system.

I'm using an XW+ also but with AC coupling only, no charge controllers, and 2 LFP batteries. So far all working quite well. The frequency shift curtailment response is fast and accurate shuts down both grid-tie systems at 60.5Hz well before the batteries get overcharged.

Not sure why the Schneider literature would recommend against AC coupling with LI batteries. Perhaps due to the potential fire hazard associated with Li NMC chemistry. LFP is much safer, that's what I use as do the majority of members here on the forum.

 

[Trygves]

My system was AC Coupled when I had the initial problem. I switched to DC Coupled just recently. Now the battery seems to be charged first before any power goes to the Schneider XW+6848. Every night the battery within a couple of hours goes from 50 volts to about 54 volts max. That during the day it stays but constantly varies around 54 volts. At night it seems to go back to 50 volts. Is that normal?

 

[hwy17]

Everyone keep in mind OP has 15s batteries.

 

[yodamota]

50v is 3.33VPC which seems ok