Charging external battery
What are the pro/cons/concerns? I want to charge my trolling (marine semi-deep cycle) battery (80 AH) using solar in the afternoon after its been discharged 30-50%. House batt SOC would be 90% or ...
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I tried solar direct on a pair of T-1275s which were at 90+% SOC at the time from my 230w panel (37 Voc) aimed south-westerly at the late afternoon sun. Sort of like the OP's situation.
As expected the amps were a bit less than panel Isc of 8.3a, ISTR I got about 7a due to the sun being down some. Battery voltage climbed steadily but not sharply from 14s to 15s but the rate of climb slowed as voltage got higher till it stalled out at under 16v, forget exact number.
I think this was from a combination of the panel output declining slowly in amps as the sun got lower plus the natural stalling out you get with any charger that reaches what limit it has to get the battery voltage any higher.
Anyway, nothing broke and I got the batts to a higher SOC than they would have reached that day if left on the controller.
( That controller was on Float at that high an SOC going in, and its adjustable Float voltage only goes to 14.5v, so that's why I tried the solar direct trick. It will go to 15.5 in Absorb, but once it gets to Float you can't use the Absorb until batt voltage drops to 13.2ish. Here is where it would be handy to have a controller with an adjustable voltage that goes to 16v whenever you want it to)
As expected the amps were a bit less than panel Isc of 8.3a, ISTR I got about 7a due to the sun being down some. Battery voltage climbed steadily but not sharply from 14s to 15s but the rate of climb slowed as voltage got higher till it stalled out at under 16v, forget exact number.
I think this was from a combination of the panel output declining slowly in amps as the sun got lower plus the natural stalling out you get with any charger that reaches what limit it has to get the battery voltage any higher.
Anyway, nothing broke and I got the batts to a higher SOC than they would have reached that day if left on the controller.
( That controller was on Float at that high an SOC going in, and its adjustable Float voltage only goes to 14.5v, so that's why I tried the solar direct trick. It will go to 15.5 in Absorb, but once it gets to Float you can't use the Absorb until batt voltage drops to 13.2ish. Here is where it would be handy to have a controller with an adjustable voltage that goes to 16v whenever you want it to)
