Is There a Point to Float with LA/Liveaboard/Solar

[CatNewBee]

Originally Posted by noelex 77

The amps going into the batteries is very important, but the Victron does not know this number.

The amps leaving the solar controller is not a great deal of help. 50A leaving the controller could be 50A going into the batteries or 50A going towards powering the microwave, with a net discharge of the batteries.

The Victron does have a “tail amp” termination of the absorption phase. I think the amps needed for this vary with the controller size. On my model it is 1A. So if the Victron is only putting out 1A and the battery set points are being maintained the absorption phase will be terminated (there is also an unspecified time delay).

If Victron are listening it would be great if the software included the option to disable this function because in some situations it causes problems.

Hopefully Victron are listening.

The tail current is only measured / taken into account IF the solar controller has started pulsing / limiting the output because of reached absorption voltage. If you draw more than the controller provides, 1.) the voltage drops below absorption, 2.) controller waits a threshold of time and goes then back to bulk. The tail current is the current the system takes from the charger unde the condition the charger is at ABSORPTION (voltage) and the current is less than maximum current available (charger is regulating).

So in your situation with the microwave, it will wait for some time and go back to bulk.

Next issue is if you have multiple solar controller installed ( per panel, ore more strings ), than voltage and tail currents are shared between the controllers and each of them makes its own estimations. ( Tail current = SUM(current1, current2,...currentn), Voltage almost equal on all controllers because of different cable length, sizes, currents).

[noelex 77]

Originally Posted by john61ct

example?

With multiple controllers there will often be a slight voltage imbalance where one controller will be contributing less than the others. If the tail amps level is reached by one controller, that controller will prematurely terminate the absorption cycle and drop to float.

If the other controllers can maintain the appropriate voltage set point, the batteries will still be happy, but if the solar conditions deteriorate, or an extra load is added, the controller that has become disabled by the “tail amp” setting (Victron call it the “tail current cut off”) will not contribute any current unless the voltage drops below the float voltage.

It should be easy to add a software option to terminate this feature in the same way the temperature compensation be can turned off. It would be a major improvement, as the Victron controllers are very popular for multiple controller installation and the “feature” can be a real nuisance.

[a64pilot]

Obviously the other issue of tailing amps being used to terminate charging is the unknown number of amps that the boats house load is.
So do you set the terminate amperage including average house load? If so what about when the fridge cycles off, won’t it prematurely terminate charging?
I don’t care what you do, what kind of algorithm there is etc, if you allow the charger to decide to terminate charging, it will do so prematurely. They are all or at least all that I have seen are conservative, very conservative. At some point it was decided that close enough to fully charged was better than slight overcharging.
Perhaps they have to take into account the guy who installs and forgets the thing, which I guess is smart, cause I have yet to meet a cruiser who actually babysits their bank, understands what the definition of fully charged is and checks.
However in truth battery charging almost never comes up as a topic of conversation. About as often I guess as how frequently do you change oil, which is a conversation I don’t ever remember having.

Until someone comes up with a way like Magnum did and will actually measure amps only going into the bank and terminate based on that, I will continue to leave mine in absorption and terminate manually if and when on those rare occasions they bank actually, really gets to 100% SOC.
I’ve not had that happen yet, but as have not been cruising during Summer months either, so maybe that is why.
I recognize there is a significant difference in usable Solar in Feb as opposed to July.

Now those of you with flooded banks, don’t have to be as concerned with well and truly fully charged as us with AGM banks, so I guess for you close enough, is well, close enough.

[noelex 77]

Originally Posted by a64pilot

So do you set the terminate amperage including average house load? If so what about when the fridge cycles off, won’t it prematurely terminate charging?

The tail amp termination on the Victron controller is not adjustable. It is not a “feature” (or a nuisance) on many controllers, and when it is included it is often adjustable, which solves the nuisance problem.

Where it is included, and is also adjustable, it would be inappropriate to set the value in the way you have indicated because of the problems you have outlined.

Undercharging is more common on boats than overcharging, but I think you are underestimating the effects of overcharging on the batteries’ lifespan. Unfortunately, it is difficult to quantify these effects, but with modern equipment and specifying the correct charge parameters, hitting the ideal charge (neither under or over charging) or reasonably close to this mark, is achievable especially if you understand the battery charging processs.

In your case if you never, or very rarely hit the point where a drop down to float is needed leaving the battery permanently in bulk/absorption will not cause any problems, but this is not the case for many installations.

[noelex 77]

Originally Posted by a64pilot

I don’t care what you do, what kind of algorithm there is etc, if you allow the charger to decide to terminate charging, it will do so prematurely.

Any (or almost any) charger with adjustable parameters can be set to excessively overcharge (providing the solar panels can produce enough power to do this) or to excessively undercharge the batteries.

There is normally enough adjustment to configure the battery set points way wrong both ways.