Changing the absorb time interval on FM80.

softdownsoftdown Solar Expert Posts: 3,137 ✭✭✭✭
The default time frame is two hours. BB recently advised that duration should be greatly enhanced with AGM batteries. I have 270 Ah FullRiver AGM batteries. The manufacturers generally feel they can be treated similar to lead acd batteries - taking higher voltages including Equalizing procedures. 

Just spent a couple hours trying to do that. The manual shows it can be done in Advanced Mode. But I was not able to access that window in spite of giving myself the heebie jeebies scrolling through windows. After pushing that many buttons, the FM80 may decide it is a vampire at 2am on Friday the 13th. 
First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries


  • BB.BB. Super Moderators, Administrators Posts: 30,497 admin
    Actually, relaying Marc Kurth's vast experience. And another poster here (CoachDad) who has seen multiple updates of the Concorde/Lifeline battery manuals around charging:



    First: I will categorically state that almost every early Concorde battery failure that we see is from undercharging. Undercharging is the enemy and always has been forever. Undercharging can include too low of an Absorb voltage, too short of an Absorb time, too low of a charge rate and not reaching 100%  SOC often enough. Way behind undercharging on the list is high temperature. Overcharging is rare to the point of being almost non-existent.

    Second: It is MY opinion that Concorde has gradually ratcheted up their support of “conditioning” because customers are so afraid of “over charging” their batteries, that they undercharge them. MOST people do not read (or perhaps ignore) the fact that Concorde batteries must be charged at the Absorb voltage until they are only drawing one half of one percent of the battery bank C/20 rating. Simply put, 0.50 amps per 100 AH of battery capacity.

    Dropping to Float before reaching this point is a form of undercharging and will cause sulfation. Their manual also provides suggested Absorb time settings to be used as a starting point to fine tune. Two hours is minimum for very shallow cycling and four hours for deeper cycling.  Remember that “end amps” is the key and that lots of Float time brings strings into balance.  We often read the internet megaphone about overcharging AGM’s.  Think about a typical 1200 ah bank. At 100% SOC, the entire group of 24 batteries is only drawing 6 amps!  I assure you that it will take a very long time to cook them. Especially when the sun goes down with great regularity.

    There is much, much more to discuss, but I will say that if our battery banks are charged per the manufacturer’s instructions, equalizing is not required for the first 5-7 years. Yes, it is a slightly destructive process, but less so than sulfation! 

    OK that was wordy! But go ahead tell me what I missed!

    I found the thread where CoachDad had issues with the rolling manual revisions:

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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