Many Ah counters attempt to re-set to 100% at the same point in time your batteries reach full. In theory this is great. In practice, in the real world, this is very often an utter failure.. In regards to auto-sync many Ah counter owners who cruise and PSOC cycle the banks will be far better served to simply program this out or turn this feature off until you return to the dock.. The problems surrounding Ah counters and auto-sync are so problematic the issue has even earned itself a nickname, "The Gotcha Factor".....


To program auto-sync out/off simply plug in parameters that are not possible for the charging system to meet. In this image I have programmed the Vc or “Voltage Charged” to 14.6V. Considering this is for a GEL battery, which never charges above 14.2V, the battery monitor can not “auto-sync" at the wrong time because Charged Voltage will never get to 14.6V. Simple stuff...


Unless you have one single charge source, and you tie to a dock after every use of your boat, or even RV, and leave it there charging for more than 24 hours, you would be wise to not use auto-sync. For boats with multiple charge sources, especially solar & wind, you can spend lots and lots of time trying to get this programming right and still fail to do so.


This quote from Matthijs Vader of Victron sums up how these monitors re-set& sync to your bank.


Quote:
"Synchronization works with simple logic: if the voltage is high, and at the same time there is not a lot of current going into the battery, the battery will have to be full. So the monitor resets its SoC back to 100% and the monitor is accurate again.


Now, all monitors have parameters for this, we called them Charged Voltage and Tail current. SoC is reset to 100% when the voltage is higher then the specified Charged Voltage threshold and the amps going into the battery are below the Tail Current. The lower you set your tail current, the more accurate your battery monitor will be (on a theoretical basis). The battery monitor will reset to 100% when the battery is completely full. The problem is that batteries are seldomly completely topped up, and therefore these parameters are very seldomly met.


The most simple solution is to loosen up the Tail Current setting. For example, set it to 5% of your battery bank capacity (or even a bit higher when necessary in your specific application). This way the battery monitor will synchronize more often. The drawback is that you'll get a SoC that might be a bit optimistic, but hey, it will be much better then the SoC you see at the moment! And, it will be stable."


The key take away here from Matthijs is "Seldomly met". There is also an assumption that every current/charging source can always produce more than the "tail current", which is not the case with solar or wind both of which could trick these monitor into prematurely thinking the bank has met "full parameters". I do not recommend loosening up the "tail current" as you will be technically undercharging the battery and this will lead to sulfation and shorter battery life.


“RC, Isn’t my battery full when the ampere hours on the screen are returned to zero?”


Contrary to popular misconception some Ah counting battery monitors do not reset based on Ah’s returned to the battery going to 0.0 Ah. Instead they use a number of factors such as voltage, time, current and time at both current and voltage to try and determine when the battery is actually full.


Unfortunately with multiple charge sources, and house loads, they can get confused and tricked into prematurely re-setting to 100% SOC prematurely. Some older model Ah counters do require -Ah's to be returned to 0.0 before it resets to 100% but this feature has since been removed by some Ah counter manufacturers for liability reasons as told to me by one of them.


"We don't want a customer with an out of calibration monitor over charging a battery by trying to get back to 0.0 Ah's because this could pose a potentially dangerous situation."


These are the parameters the many Ah counters use to determine “full”.


Charged Voltage – This is the voltage the battery monitor looks for in order to qualify for a “full charge” reset. Voltage above XX.XX volts = CHECK


Tail Current – Tail Current is the amount of charge current the charge source needs to be below in order to qualify for a “full charge” auto-sync reset. Current below X.XX amps = CHECK


Charged Detection Time – The monitor looks at Charged Voltage and Tail Current and applies a min Time Factor at those levels. If the time for voltage and amperage meet the minimum time applied factor this = Auto-Sync Reset to 100% SOC


The "Gotcha" Conundrum:


Now let’s look at this in a real world scenario. Your boat has a solar array and it’s early to mid morning. The batteries are still in bulk charge mode, and the solar is just barely able to get them to your Charged Voltage setting of 13.2V. Because of the low current supplied by the solar array, due to it being early in the day, all the PV system can muster is 13.2V, and at a current below your Tail Current. If the system proceeds like this for longer than the Charged Detection Time, regardless of where you are in the SOC range, the monitor resets to 100% SOC.


System loads on your boat, such as water makers, refrigeration etc. can also pull charging voltage and net charge current below the charged detection parameters, if your charge source is not able to muster it all. This house load can also indirectly cause the monitor to reset on voltage, tail current and charged detection time.


There are many scenarios we can paint that can cause these monitors to reset falsely & prematurely thus creating bad counting errors.


For the average cruising boater, away from the dock, simply turn off or program out auto-sync and sync the monitor manually.


***WARNING*** Programming out auto-sync reduces the ability of a monitor to calculate a charge efficiency factor for you, if it has this feature. You may need to manually allow the unit to occasionally complete a reset on its own when tied to a shore charger in order to arrive at the best CEF.


For the die hard electrically minded individuals out there it is possible to program auto-sync to still work, but this is a recipe you'll need to figure out for your own system and your system only. There are far too many variables to give a cookie-cutter recipe for auto-sync especially when we start mixing in solar or wind etc.. If your monitor is an automatic calibrating CEF unit I recommend carefully setting your "full" parameters and letting the monitor re-sync on its own.


I set foot on far too many boats with battery monitors reading 100% SOC where I fire up the motor and the alternator is pumping 20-40A plus into the batteries. These are not 100% SOC batteries. A full & healthy battery will accept less than 1% of its Ah raring at absorption voltage. A Manual Sync current of 1.5% - 2%, of Ah capacity, is a safe number for a cruising reset target.


For cruising/PSOC use disable the "auto-sync" feature and use manual "known-full" re-sets.


“Come on RC, what the heck is a known-full reset?”


Know Full reset:

#1 Turn all DC loads OFF

#2 Fire up battery charger or engine & allow to run 4-5 minutes

#3 Voltage should be at ABSORPTION level or 14.4V+ = CHECK (GEL 14.1V)

#4 Net accepted charge current less than 1.5% -2% of Ah capacity = CHECK

#5 Okay to MANUALLY reset to 100% SOC


NOTE: Battery voltage should be at absorption voltage not float voltage, unless it has been floating in excess of 24 hours.


A known-full reset takes but a few seconds once the charge source has run for a few minutes. Easy and known accurate.


You can use 2% as your known-full current threshold but 1% or 1.5% is a fuller and healthier battery. For example most AGM batteries are not even considered full until they hit 0.3% - 0.5% of their capacity in net charge current at absorption voltage. This is 0.3A - 0.5A at absorption voltage on a 100Ah battery.


For a 1% reset with non-GEL lead acid batteries:

100Ah Battery = <14.4V+ and >1.0A

200Ah Battery = <14.4V+ and >2.0A

300Ah Battery = <14.4V+ and >3.0A

400Ah Battery = <14.4V+ and >4.0A

500Ah Battery = <14.4V+ and >5.0A

Etc. etc.


By using a known-full manual re-set you are not guessing when your battery is full, you know when they are full. Resetting a your Ah counter to known-full regularly helps keep it in better synchronization with your bank.


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