Rogue MPPT, 490W and charging mysteries

Almot wrote:
Now that we were finally all in one place - me, Rogue 3048 and my rig - it was time to have some fun.

1)Battery: old starter, tested beyond dead, plates above the water. No wonder, 8 months in Mexican heat. Added water and put it on Rogue with 2*245W 24V panels in series. It started happily with 20A at 1pm, there was some shade and clouds this and the next day. Went into Vabs=14.6 after a while, then sun dropped behind the mountains. Next day tried to bring I Abs below 0.4A - guestimated it around 40 Ah. Starter battery only has cryptic Cold crank 700A, crank 840A, Reserve Capacity 110 min. Rogue allows minimum I abs=1A, T Abs=4 hours max, timer overrides Iabs. Tried 2*4hours, barely went down to 1A.

Then tried to equalize - since it's dying, why not?, set up Rogue to V Equalize =15.5.
Surprise #1, it can't bring V up to more than 15V. Panels output 63V, current - don't remember. Battery was full, I wonder if this was the reason. Well, truck starts, battery is losing charge fast, but alternator brings it back to life, so let it be.

2)Battery: AGM 100 AH by UPG aka Universal Battery. I have 3 of them, they survived Mexican heat, losing 25% in 8 months, Voc=12.45, put one on charging. Shortly after hooking up it went into Abs, so much for 490W system. I set I abs=1A min, since it's 100AH, and Abs time to 4 hours - pure charging, no loads. Some clouds on the first day, current never went over 7A, - well, it's Abs. Had to reset the Abs timer a few times, and by the end of the NEXT day it was still at 1.5A. So I gave up and put darn AGM on 8A load - 12V 100W bulb.

3) Testing AGM 100 AH. Like I said, it spend more than 8 hours in Abs. Next day battery Voc=13.05. Surprise #3: V on load = 12.45. This is 83%. What the heck? It was 75% before 2 days of charging. Alright, let the real SOC test commence. V load dropped from 12.45 to 12.0 (=50% SOC under load) after 4.75 hours. This is 38 AH. So it was 76% full after it has been charged to 1.5A min.

So, it was 75% SOC before charging, 83% right after many-many hours of Absorption on 490w system, and load test revealed that it was not even 83%, but ~76%.

4) Maybe will make a separate tread out of this. Hooked up remaining 2*100AH AGM to same 490W in series +Rogue. Voc on rested battery 12.45 as before. No clouds, some shade, set V abs to 14.6 - and it went into Abs at 14.4. Set V abs to 14.8, it went up to 14.6 for a few seconds, then again 14.4. Time to test the Rogue ? ;)

A couple of questions:

Regarding the equalize attempt: it would be good to know how much current the controller was pushing into the battery. Should have no problem getting a small battery to 15.5v with 490w. Have you tried equalizing a battery that's not on the verge of being put on the scrap heap? Does the percent counter start counting up, or does it just stay at 0%?

Secondly, is the battery temp sensor connected? If so, it may be altering the absorb setpoint if the batteries are warmer than 25C.

If you're operating without the sensor, you may need to adjust the VTRIM setpoint a little to correct the error you're seeing. Bump it up a little (by +4 to +8 or thereabouts) and that should fine-tune the setpoint (there's a section in the manual that details the procedure if you want to make it more accurate). Not sure why it's trying to do 14.4v at *both* 14.6 and 14.8, though.