Probably a simple answer.

Re: Probably a simple answer.

Well if you don't have any maker's specs for it, you'll have to test for it.

You've got a 1380 Watt array on a 12 Volt system, yes? Should be able to make 88 Amps which is above the FM80 rating. Regardless, 80 Amps on a 900 Amp hour bank is a good 8+% rate.

So set the Absorb time limit to its maximum. Use the batteries; cycle them down 25% or so. Then begin the recharging next morning. When it gets to Absorb, watch the current and time. See how long it takes to drop down to about 2% of capacity: 18 Amps with no load draw. Round that time up to the nearest for maximum Absorb time.

Then program the End Amps to accommodate this current level, plus an allowance for any constant loads that would be on about the time Absorb takes place. These two factors together should do it. It won't be perfect and you'll want to watch the system for awhile to look for inconsistencies, but it's about the best you can do under the circumstances.

Re: Probably a simple answer.

Well ...
Set the maximum Absorb time to 4 hours.
Let the system recharge after normal use, without any loads on if at all possible. When Bulk switches to Absorb, keep track of the time passing and the current going down. When the current reaches about 2% of the battery capacity it probably isn't going to go down much further; the battery is fully charged.

Now say it took 2:15 to do that. You reset the maximum Absorb time to 3 hours, so it won't try to run Absorb beyond that. And you set the End Amps function to that 2% rating, plus an allowance for load draws. This could be 18 Amps or 20 Amps. That way whenever it reaches that current plateau, regardless of the amount of time (up to 3 hours) it takes it will switch from Absorb to Float based on charge current level.