Very Low OCV on Full Batts???
I've been seeing lower than usual resting ocv this winter, compared to last. Figured it was either wear and tear, too high a charging voltage, or a parasitic draw. So I tried throwing a lower vol...
Forum Discussion
Well, I've gone back over my notes, in light of the new info provided by Bend, and here are my conclusions;
My batts were resting at 12.71 - 12.73v, after being charged at sufficient, i.e; temp compensated, voltages. I thought those resting voltages were too low, but in reality, those resting voltages were actually a little higher than they should have been, given the very cold temps. So, those voltages were actually an indication that the surface charge had yet to fully self-discharge; obviously due to slowed self-discharge rates. So after a couple more weeks at such cold temps, they still would have been fully charged, even once the voltage dropped to below 12.7v. So everything was fine, the batts were indeed full, and charging was not necessary. Nevertheless, I did charge them, at that time, and the readings, while charging, indicated they were indeed full. Hence my confusion at the time.
But here's the kicker. When I charged them, I lowered Vabs to 14.6v, in hopes to see better resting voltages, but then the voltages plummeted to 12.54 over the next 6 days. How and Why? Well, for one thing, temps stayed consistent for the next 3 days, but then dropped consistently the following 3 days. When I compared self discharge, resting voltages, and daily temps, they all seem reasonable for the first 3 days. But then (EDIT; it appeared) there was a sudden increase in discharge rate as temps dropped, which does not make sense, and by the 6th day, resting voltages had dropped drastically, to well below what they should have been at 18F.
So, clearly, dropping Vabs results in much lower resting ocv. Fine. But what really confused me was how charging FULL batts at 14.6v for 2 hours could result in lower resting ocv??? Now think about it... that is like fully charging warm batts at the appropriate Vabs (say 14.8v) and having an ocv of say 12.75v a few days later, after surface charge has dissipated, but then throwing a 13.2v float charge on the full batts for a couple of hours, and then having a lower ocv a few days later.
So the question arises, is that normal? IOW, does float charging result in lower resting ocv, than if one was to terminate charging at the end of the abs stage, and not allow the charger to float the batts? OR, is this perhaps a cold temp phenomenon?
My batts were resting at 12.71 - 12.73v, after being charged at sufficient, i.e; temp compensated, voltages. I thought those resting voltages were too low, but in reality, those resting voltages were actually a little higher than they should have been, given the very cold temps. So, those voltages were actually an indication that the surface charge had yet to fully self-discharge; obviously due to slowed self-discharge rates. So after a couple more weeks at such cold temps, they still would have been fully charged, even once the voltage dropped to below 12.7v. So everything was fine, the batts were indeed full, and charging was not necessary. Nevertheless, I did charge them, at that time, and the readings, while charging, indicated they were indeed full. Hence my confusion at the time.
But here's the kicker. When I charged them, I lowered Vabs to 14.6v, in hopes to see better resting voltages, but then the voltages plummeted to 12.54 over the next 6 days. How and Why? Well, for one thing, temps stayed consistent for the next 3 days, but then dropped consistently the following 3 days. When I compared self discharge, resting voltages, and daily temps, they all seem reasonable for the first 3 days. But then (EDIT; it appeared) there was a sudden increase in discharge rate as temps dropped, which does not make sense, and by the 6th day, resting voltages had dropped drastically, to well below what they should have been at 18F.
So, clearly, dropping Vabs results in much lower resting ocv. Fine. But what really confused me was how charging FULL batts at 14.6v for 2 hours could result in lower resting ocv??? Now think about it... that is like fully charging warm batts at the appropriate Vabs (say 14.8v) and having an ocv of say 12.75v a few days later, after surface charge has dissipated, but then throwing a 13.2v float charge on the full batts for a couple of hours, and then having a lower ocv a few days later.
So the question arises, is that normal? IOW, does float charging result in lower resting ocv, than if one was to terminate charging at the end of the abs stage, and not allow the charger to float the batts? OR, is this perhaps a cold temp phenomenon?
