LFP Operating Voltage

[Scubaseas]

Originally Posted by s/v Jedi

A lot of people are killing their LFP batteries with incorrect charging, without knowing how it should be charged or even looking up manufacturers instructions.

Most don’t even know terms like CC, CV, “termination voltage” etc. and don’t know how to program a battery monitor to accurately show SOC% but then still look at that readout and use it.

Also, talking about voltages while a battery is being charged or discharged is meaningless, as is the measurement itself when it isn’t known what this was measured with and exactly where it was measured.

The only recommendation for these cases is to hire a professional to analyze your installation, fix it where needed and explain it’s use as a completed system. There’s just too much to learn to know internal workings; one would need to study electrical principles first, then how Coulomb counting battery monitors work, how LFP cells charge and the effects of charge rate in relation to termination voltage etc.

And Peukert Effect too.

I don't disagree with you but most marine "professionals" whose work I've run across are the problem not the solution.

[sailorboy1]

My house batteries are never "stored".

I don't see any issue with starting the day with the batteries 60-70% and during the day solar gets the batteries to 95-100%. Maybe this is old lead acid thinking, but is there a issue?

[s/v Jedi]

Originally Posted by Scubaseas

And Peukert Effect too.

I don't disagree with you but most marine "professionals" whose work I've run across are the problem not the solution.

True, most are licensed installers, not capable of system design. But every electrical contractor should have at least one engineer employed exactly for this type of work.

[wholybee]

Originally Posted by sailorboy1

My house batteries are never "stored".

I don't see any issue with starting the day with the batteries 60-70% and during the day solar gets the batteries to 95-100%. Maybe this is old lead acid thinking, but is there a issue?

I don't think there is any issue. It depends on what voltage you stop charging and consider 100%. If you charge to 3.65Vpc everyday, that might be an issue. But from your other posts, I don't think you do that.

[sailorboy1]

Solar does absorption of 14.4 and holds for 30 minute before going to 13.5 float. But it only gets to 14.4 if I motor or run battery charger in morning. But it is getting sunnier and am starting to get more solar each day. I don't see a problem doing this every day really, but of course it wouldn't happen each day.

[s/v Jedi]

Stop looking at termination voltage when you don’t have the manufacturer specified charge rate for that voltage (often 0.5C). This means you must charge with 140A for 280Ah cells. If you go slower, your termination voltage must go lower as well, because you are absorbing before reaching that voltage.

You must first calibrate the battery monitor, then fully charge on shore power. Next you monitor the daily charge cycles and stop charging at >95%. You will find at which voltage that is so then you can tune the charge parameters in the solar controllers.

When the solar controllers switch to float, choose a voltage where the batteries start discharging but solar carries the full load when the batteries have come down to 90% SOC. This avoids wasting solar energy while it relaxes the batteries a lot and you go into sunset at 90%.

[sailorboy1]

am following my manufacturer recommendations

[Maine Sail]

[PaulCrawhorn]

Originally Posted by sailorboy1

am following my manufacturer recommendations

Max voltage is not what the stop-charge voltage should be

if you want good longevity.

A stupidly implemented balancing circuit may "require" holding a voltage over 3.45Vpc

but there is no other useful purpose to doing so wrt the health of the cells themselves you should define that as 100% Full.

And do not let the cells sit for long anywhere near that high,

if possible, only when loads will be drawing SoC down within a few hours