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

[Dsanduril]

Thanks everyone for the input and the opinions. I'm actually surprised by the number of folks who said this is how they run their systems.

Our solar controller manages absorption by time, I've been running it with the time set to 6 hours for several months and have been happy so far. However, I probably didn't do enough research before going down this road, so posted to see what information people had and get a general sense of pros and cons from the real world. Greatly appreciate the feedback.

FWIW, 6 hours of absorption usually means that I run absorption until late in the afternoon when solar production starts to drop to load requirements. At this point I'm usually seeing 1-2A into a 520AH bank, which is really not that far below 0.005C. For the last hour or so before actual sunset I see voltage drop below the absorption level while amps out of the battery are still zero (until the taper gets low enough that voltage drops below about 13.2). Thus 1-2 hours charging below 0.005C at absorption voltage while sun is actually 'up' for 2-4 hours after the same point.

I agree with all the cautions - this really only does apply to LA chemistries, and if I change the usage profile (leave the boat for a long time) then it's on me to remember to go back and set a shorter absorption time and drop back to float.

Thanks again for all of the input, very much appreciated.

[conachair]

Originally Posted by Adelie

Conachair: Was that meant to be funny or was that a serious question that inadvertently mixed the circumstances of my analogy with the details of the actual question asked?

Not inadvertently, just using a more fun metaphor with a technical point - is it better to keep at absorption rather than risk not getting charged.

100% SOC defined by having charging amps drop to about 0.5%C.

Is it? On an email from trojan technical they said best way to check for fully charged is to watch the SG. Isn't 0.5% just a handy rough guide as SG isn't easy to measure remotely?

Back to the question - with solar on a boat is it better to keep the batteries at absorption voltage rather than drop to float? AFAICS no one knows, there's no data available other than snippits on various RE/off grid forums and the like. At a guess most boats that say they're fully charged by lunch probably aren't if they watched SG.
I'll stick to absorption guessing that an hour or two gassing a little will cause less damage in corrosion than risking not getting charged regularly.

Millions of cars and vans don't seem to do too badly?

[john61ct]

Originally Posted by conachair

best way to check for fully charged is to watch the SG. Isn't 0.5% just a handy rough guide as SG isn't easy to measure remotely?

Back to the question - with solar on a boat is it better to keep the batteries at absorption voltage rather than drop to float? AFAICS no one knows

Not at all, and in fact amazed that anyone could see the wealth of correct information conveyed above in that light

The answer to that question **depends on the context**, the owner must know what is going on with V & A in the current situation, and can make a completely rational decision based on that objective information.

If the chemistry is FLA then the answer is yes much more frequently. Just keep them watered.

AGM is much more susceptible to damage from persistent overcharging.

GEL even more so.

If your usage pattern is such that your bank is only getting to 100% Full* a couple hours before sunset, then no problem, no matter the chemistry.

But with AGM or GEL, you need to keep an eye on your pattern.

And in all cases make sure you don't keep Float=Absorb when you stop cycling.

SG can only be measured with FLA.

*For measuring 100% accurately,

declining amps reaching endAmps spec'd by the mfg, or

stopping declining for an hour

are the canonical definition of Full, not just easier to measure.

But with FLA, useful to cross-reference with SG if you want, just be aware as with voltage, accurate SG only comes after a resting period, up to 72 hours isolated.

[john61ct]

And as a global generalization, within the above provisos

Yes, better to err on the side of sometimes overcharging a couple of hours

rather than failing to get to endAmps at least a few times a week

[Jim Cate]

rather than failing to get to endAmps at least a few times a week

You keep making this statement, and for all I know it may be true...

But, "a few times a week" is pretty much every day, or at least every other day, and that is not a realistic goal for most non-plugged in cruisers, at least in areas with frequent overcast days and on boats with less than huge solar arrays.

We need realistic guide lines for folks who don't have gen sets or very long shore power leads. Here I agree that occasional overcharging (ie staying at absorption voltage past nominal full charge) will not be harmful IF electrolyte levels are monitored. The brutal truth is that few of us will often reach that state, at least in winter.

Jim

[john61ct]

If you don't realize how much PSOC abuse shortens your bank lifespan, you may not even try.

Once a month is better than never, once a week better than that.

If you can't you can't, but it should remain known as a goal.

And you need to know whether or not you're getting there, and that 99% is not 100%.

Just ignoring the issue does no one any good.

And many can do it, without even buying much new gear, there are many ways to get there.

[Dsanduril]

In line with Jim's comments, I do find this discussion of the last 2-5% of SOC (and I started it) interesting. When I started cruising (a very long time ago) every single boat had FLA batteries - there were no other options. And 90% had the engine spinning an alternator as the only charging source. The folks with generators were the 'gold platers'. The really serious energy users upgraded the stock 35A alternator to a 60A AC Delco unit.

For boats with no refrigeration the typical profile was to run the engine an hour a day to charge the batteries. For boats with cold it was frequently an hour in the morning and an hour in the evening to pull down the holding plates and charge the batteries. Under that scenario those batteries never saw anything above 95% SOC and that was a very rare occurrence, more like 90% at best. When the amps started to drop from the engine you shut it down.

Those systems ran at PSOC continuously. Discharge overnight, charge for an hour. Start the discharge again. Only if you decided to motor for a long time did you get a full charge - and that was a pretty rare occurrence. Batteries seemed to last about 4 years under that regime (ballpark average). Which is about 1400 cycles from 90% SOC down to 50/60/70% and back up.

Now that we have renewables and can charge at lower currents for longer times we argue about the last 5% of SOC. It is nice to get the longest life out of our 'stuff', and we certainly put more demands on our systems than in the 'good old days', but there were an awful lot of cruising boats with FLA systems that essentially never saw a full charge (or maybe once a year in the boatyard - from a crappy ferro-resonant charger) once the batteries were installed and they still managed to do OK, keep the running lights and autopilot on, etc.

Don't get me wrong, I love my modern conveniences, and a I do want to get the longest life out of the LA batteries I currently have (courtesy of the PO, otherwise I think I would change chemistries), so I want to use the 'best' charging practices, but PSOC operation does work if you have to, and you just accept replacing the batteries a little more frequently (and of course exactly how much more frequently is the quibble).

[john61ct]

And too many variables to quantify IRL.

But well coddled, a good quality FLA bank can easily go well over a decade, seen 14-15 years but likely pushing well past 70% SoH there.

Your bank your call, just make conscious choices not ignorance.

[Captain Bill]

I killed a pair of 6 year old Concorde lifelines this spring by overcharging with a solar charger. I replaced my old 300 watt Solar panels with 640 watts and a new mppt controller. My old controller used a shunt to determine absorption amps whereas my new one uses time. In the dead of winter it took until nearly 4:00 to get them to 2.1 amps (420ah bank), but by mid march in the Bahamas I was getting there at about 2:00-2:30 even after going to DST. I unfortunately did not understand that my new controller had a feature that allows it to skip going to float the next day if the voltage drops below a set number overnight. It was supposed to be set to 11.5 V at the factory, but my unit was set to 12.5. It was never going into float so I was doing the equivalent of having my float voltage and absorption set the same. It was difficult to troubleshoot the issue from the Bahamas, so it did not get fixed. About the middle of April the bank fell off a cliff. Instead of being at 12.4 under load (refrigeration about 5a) it was down to 10.1. I got it back up, by the end of the day but the next morning I was below 10. In the states this would have been a problem, but in the Exumas it was nearly a feaking disaster. I bought the only FLA of any size that they had just to limp home. Of the 3 on the shelf two showed 0 volts and the one I bought showed 12.27. It was not a very good battery but it got me back to the states. Before putting in my new bank I had a long phone call with the controller support people and they finally identified the problem setting. I also had a long conversation with a tech at Concorde which confirmed my suspicions about overcharging and provided me with a new tidbit of information I had never heard before and that is that as AGMs and specifically Lifeline AGMs age then the amperage at which they are considered 100% charged goes up. So while 2.1 amps is the recommended absorption amperage for a new battery, on ones the age of mine I should have been stopping at 4.2-4.5 amps. I was overcharging these batteries every day, even if I had stopped at 2.1 amps. I confirmed that the typical failure mode due to age is a slow steady loss of capacity. Batteries falling off a cliff like mine did is a symptom of electrolyte depletion caused by overcharging. This may not be an issue for FLAs where you can add water, but it is deadly to AGMs even with recombination.

[CatNewBee]

... Same for GEL & SMF.
Just do not boil them. It is sufficient to charge once a week to 100%.
When in storage, no need to run on float all the time. You can charge them every couple of weeks for a day or two to full and then turn off the charger and give them a rest.

Doi g too much is as bad as doing nothing.

[john61ct]

My first two posts here #6 & #8 pointed to this

Originally Posted by john61ct

And the key qualifier is, using what batteries?

Reinforces the fact only those with a compelling reason should be using AGM or GEL.

FLA is much better value, cheaper both up front and over time, more robust and longer-lived, easier to care for, harder to damage.

Obviously you **can** get very long life out of fussier chemistries, but people here keep emphasizing they don't want to pay so much attention to their batteries.

[Captain Bill]

Originally Posted by john61ct

My first two posts here #6 & #8 pointed to this



Reinforces the fact only those with a compelling reason should be using AGM or GEL.

FLA is much better value, cheaper both up front and over time, more robust and longer-lived, easier to care for, harder to damage.

Obviously you **can** get very long life out of fussier chemistries, but people here keep emphasizing they don't want to pay so much attention to their batteries.

I absolutely agree, if my battery compartment was not inside the living space with absolutely no ventilation I would be using FLAs too.

[TreblePlink]

Originally Posted by Captain Bill

I absolutely agree, if my battery compartment was not inside the living space with absolutely no ventilation I would be using FLAs too.

Am I right to be concerned about Hydrogen and Oxygen generation during "topping off" charging? Seems like you would never want FLA batteries to start gassing unless very well ventilated. I have personally witnessed a small building explode due to this ...

[a64pilot]

I think all of our banks are within living space, or at least the majority are anyway.
I have AGM due to size constraints or I would have gone to flooded.
My next bank may be Gel though, I understand they are finicky, but charger technology is way beyond what it was just a decade or two ago.

[noelex 77]

Even if your controller does not measure “end amps” or “battery return amps” (and most do not), the charge algorithm and in particular the absorption time should be set so that on an average cycle the controller is dropping down to float when the end amps have reached an appropriate point.

If set up like this it will normally be dropping to float at the correct time. This is how the controller should be working. If set up correctly there is no advantage and some drawbacks to forcing the battery to effectively stay in absorption.

If you cannot adjust the controller to regulate correctly, an absorption time that is too long is probably better, at least for flooded batteries, than an absorption time that is too short.

I think some of the problem is that the popular and otherwise excellent Victron chargers do not have a normal absorption timer. The very unusual Victron regulation requires a very long absorption time because the absorption timer does not monitor voltage. So the appropriate settings for Victron users will be very different to most controllers.