I have a 90ah DIY (4x3.2v) lifepo4 battery that I've assembled. It's comprised of used cells that are somewhat old, so I've done a lot of testing indoors with charging and discharging to see what I can comfortably utilize and calculate my needs. Running 712 BMV, 65a battery protect, 75/15 SmartSolar MPPT.
I'm basically set on treating this battery as having 60ah usable capacity and have done several charge/discharges like this, recharging with an RC hobby charger. If I charge to RESTING 13.34v at terminals (or 13.29 on BMV) I can consistently pull 60ah out of the pack @ 75w continuous draw. With the BMV set to 60ah capacity, I reach zero percent and about 10 minutes later my Battery Protect cuts off (set to 12.55 cut off, rebounds after 75w load is cut to 12.8 or there about). This is perfect for my needs and then some.
So today I decided to do a real world solar test, using the 75/15 MPPT (receiving temp and voltage info from BMV via network). My controller settings are Absorption Voltage: 13.29v (measured at terminals its 13.4). My float voltage is set to 13.25 (measured at terminals 13.28-ish). My charge current is set to 15A to let the max of my 200w series'd panels do their thing.
What I'm observing, is that even though my battery is at 20% capacity as measured by the BMV, the MPPT is only allowing in 45w and is floating - no load. Panels @ 40.78v. It's peak sun right now and not a cloud in the sky, and if I adjust the absorption and float way up, it'll go from 45w to 150+w.
So the charge controller is throttling charging to the battery because the voltage it's reading while charging, and my settings for float/absorption voltage. But the battery only has 20% of my configured capacity in it.
I'd like to charge at a much higher rate in cases like this, since I'm at 20% of my capacity and in the real-real world, throttling my charge current when I'm at a low SOC will surely bite me in the butt if it gets cloudy the second half of the afternoon. What value(s) can I change to achieve this while ensuring that I never exceed a resting voltage of 13.29 @ BMV (13.4 @ terminals). I'm OK if the voltage goes up to 13.7v when charging at 10+a, this was observed when charging with a hobby charger nearing full (and settled off-charge to 13.29@BMV)- and is right about the point when my 6a active balancer board starts to lose control of one cell in particular. But I don't ever want the battery to get charged to 13.7v resting.
Thanks, sorry for wall of text - it probably could have been condensed in to something much shorter but I didn't want to skimp on detail!