Thought I knew a lot about batteries and charging
systems (grew up and still in automotive industry).
Recently outfitted boat for long range extended time on the hook
900 a/hr bat bank, solar
, inverter/125a charger
No sweat everything working great but bat voltage down to 12.4 in the am after 120 a/hr draw overnight. (Victron meter)
Read 75% SOC right? Should be 86.7 SOC
Problem is over time the bank goes down and not starting w/100% charge.
alternators set @ 13.7v
780 watts but not enough sun on cloudy days to over come usage and have a net amperage to bring the bank up to 14.8v absorption long enough.
So let's start the gen.
reads the 13.7 volts and thinks the bank is fully charged so goes into float.
Long days run? Victron reads fill charge (I've tried to reset this, save for another topic),
After running for 6-8 hours bank should be charged right? NOT, only reaches 13.7 volts (alternator setting) not enough voltage to bring the bank to 100%. And if you plug
into shore power
at the Marina after a long run you figure I'm OK I've got the charger on, WRONG charger reads 13.7 so it goes to float!
Solar you say, if there is not enough sunlight and wattage output it will never reach absorption stage long enough to reach full charge even though you have replaced the a/hrs used.
At home dock
no power usage (Everything shut down not living on board right now), 1 day solar back to 1% amperage charge of bank size
I.E. 9 amps @14.8v
Used 120 a/hrs last night (test run with inverter
running and fans etc, to run down to 88% charge and VIOLA 12.6v in AM
So I emailed the charger co (magnum ms2800) and they told me yes! To fool the charger so it goes into absorption, turn every thing off for 2 min and wait for voltage to go below 12.7 (which may require loading batt bank, and Viola goes into absorption mode.
Moral of the story is when your net amps into the bank are 1%-2% of total a/hr capacity at the rated absorption voltage your 100%
Unless you are sulfated (check specific gravity with a GOOD tester not one of those el chepos)
Hope this helps someone, took me months to figure it out, I'm sure most of the more experienced cruisers out there already know this.
Thanks for listening