Overcharging Concerns

[willh]

Have been deep diving into charge settings and lithium charging information. At this point I wish I had just set the Victron recommended profile or the same thing the off grid garage guy uses and continued life blissfully unaware of all the potential details. I must say I am thoroughly confused about what my best approach to charging is at this point.

My greatest anxieties are formed through reading this article:

Charging Marine Lithium Battery Banks | Nordkyn Design

nordkyndesign.com

Given the information in this article it is quite likely I could frequently be overcharging my battery. I have a 230ah 48v battery to be charged with 920w of solar. In the event my charge current is below 3.22amps during the constant current phase my battery would already be overcharged by the time it hits 3.45v based on this article. Seems to be a very likely scenario in any solar setup. Either way even on a great solar day with this setup the battery will be very near full upon reaching 3.45v, which leads me to believe I should take away absorbtion time all together/set lowest limit. That creates it's own problem as now the cells won't have a chance to balance.

As a test I set my multiplus to charge at 7amps max (simulation of my solar array generating 380ish watts of the 930w theoretically possible), absorb voltage 3.45/cell. Upon reaching 3.45v the charger switched into absorb and it took only a few minutes for current to drop down to 0.014c (3.22amps) as described in this article.

My cells never required balance staying below 10mv delta on jk bms. Currently set for balance above 3.45v, not sure if the cells will eventually go out of balance in this charging regime but if they do the bms isn't likely to have enough time to balance them anyways. Initially I thought maybe I'd set cv stage to 3.5v but that only exsasperates the low c charging issue. Am I overthinking this? What am I missing?

 

[sunshine_eggo]

Have been deep diving into charge settings and lithium charging information. At this point I wish I had just set the Victron recommended profile or the same thing the off grid garage guy uses and continued life blissfully unaware of all the potential details. I must say I am thoroughly confused about what my best approach to charging is at this point.

My greatest anxieties are formed through reading this article:

Charging Marine Lithium Battery Banks | Nordkyn Design

nordkyndesign.com

Given the information in this article it is quite likely I could frequently be overcharging my battery. I have a 230ah 48v battery to be charged with 920w of solar. In the event my charge current is below 3.22amps during the constant current phase my battery would already be overcharged by the time it hits 3.45v based on this article. Seems to be a very likely scenario in any solar setup. Either way even on a great solar day with this setup the battery will be very near full upon reaching 3.45v, which leads me to believe I should take away absorbtion time all together/set lowest limit. That creates it's own problem as now the cells won't have a chance to balance.

As a test I set my multiplus to charge at 7amps max (simulation of my solar array generating 380ish watts of the 930w theoretically possible), absorb voltage 3.45/cell. Upon reaching 3.45v the charger switched into absorb and it took only a few minutes for current to drop down to 0.014c (3.22amps) as described in this article.

You are right to be concerned. This condition might shorten your battery cycle life by 864,000 seconds.

My cells never required balance staying below 10mv delta on jk bms.

Cells in the operating range are rarely more than 10mV delta even when actually significantly out of balance.

Currently set for balance above 3.45v,

JBD balance current is anemic. Set to 3.40V.

not sure if the cells will eventually go out of balance in this charging regime but if they do the bms isn't likely to have enough time to balance them anyways. Initially I thought maybe I'd set cv stage to 3.5v but that only exsasperates the low c charging issue. Am I overthinking this? What am I missing?

To a clinically paranoid degree inspired by an alarmist article.

If you truly care, set the tail current on your MPPT to the appropriate amps.

If you with to minimize cell stress, charge to 3.45V/cell and tailor your absorption time/tail current to reflect something sensible.

 

[willh]

So what you're saying is don't worry about it haha. To me there is so much information and different opinions out there that it's nearly impossible to reach a consensus. I have seen that website tossed around on this forum as good information by others, never referred to as alarmist but I get what you're saying with reference to this article. It would be awesome if I could confirm you were correct about 864000 seconds, I'd be okay shaving off 10 days of cycle life. Lol. Fact remains there are more opinions and guesses than concrete info. Would be nice to have a thread where people describe their system and how long they have been using it/what settings. And only people with cells in service over 5 or something years could post lol. That way I may start to gather a better understanding of what works.

 

[sunshine_eggo]

864000 seconds was a joke.

What the article doesn't consider is calendar aging. These things degrade as they age, no matter what you do. Sure, you may thing you're going to get 15 years of cycle life, but aging is going to shave more off than your choice of tail currents.

Hunt around and you'll find folks with 8-10 years on their system. Here's an account of a system that lasted 8.5 years until they killed it due to improper storage.

 

[Substrate]

I wouldn't call his article alarmist, but it is on a whole different application concern level, where this can mean the difference when you are out in the middle of the Pacific, and can't get Amazon to do a 2-day drop shipment via helicopter of a budget clone replacement when you've been using it for 6 years and desire more life.

Usually these days many of these concerns are gone with the boater utilizing battery systems from the likes of Mastervolt, Lithionics, and Victron.

So as sunshine_eggo intimates, there's practical generic care that will serve us well that has to be balanced against the recommendations from labs, boating, and other applications. Many of which don't take into account that our power source gets turned off nightly whether we like it or not.

 

[willh]

864000 seconds was a joke.

What the article doesn't consider is calendar aging. These things degrade as they age, no matter what you do. Sure, you may thing you're going to get 15 years of cycle life, but aging is going to shave more off than your choice of tail currents.

Hunt around and you'll find folks with 8-10 years on their system. Here's an account of a system that lasted 8.5 years until they killed it due to improper storage.

Great video and their blog goes into more details, exactly the type of information I'm looking for. 8.5yrs is great and likely would have got more! The info in their blog about how they lost roughly 30% capacity is pretty crazy. I'm assuming temperature was the biggest factor.

While I understand this system won't be relied upon on a boat in the middle of the pacific I'm still interested in getting max life. While calendar aging for this system probably makes my concern invalid it is still a problem to solve. You say to select 3.45 and a sensible tail current when the article I referenced shows that in low c charge scenarios tail current can be irrelevant and the battery will overcharge. How can I be sure that this won't result in a 30% capacity loss in a relatively short time just like these folks?

The only way I can think of minimizing such occurrence is to avoid absorb all together (still a possibility of overcharge but far less likely). Maybe do a balance charge every couple months with the generator at higher voltage and c rate. How frequently do cells need to be balanced anyways/what could go wrong?

 

[willh]

Also, of course 864000 seconds was a joke. I'm really not that stunned. Lol. Just really into this at the moment.

 

[Substrate]

I had those same GBS batteries back during that timeframe. About 8.5 years was the same for me, and I was going "commando", with no bms, no bleeder boards, and only a pack-level LVD and my charger serving as the HVD. A 6v incandescent backup bulb was used for my occasional balance on an individual cell.

Maybe more info when I charge the laptop back up. And hopefully no coffee so I don't go into a 7-page discertation like I usually do.

 

[Substrate]

Ok, if you want to chase the exact tail-current end-point, you'll want to start counting current in/out with a coulomb meter. Since LFP is super efficient, (unlike lead acid), you basically put back what you take out.

Measure the capacity of your battery. When you recharge from your desired LVD point (be it bms disconnect or preferably a little higher) at whatever current and CV voltage you desire, watch your coulombs to tell you when to stop. This may be more accurate than any tail-current guidelines. Of course you can now conveniently calculate any percentage less than 100% if you want to stop sooner.

Something like the Victron BMV-712 battery monitor will do fine. Cheaper alternatives are out there, but will you be paranoid enough like me to trust them after 4 years of use? Likewise, when you measure voltages, use a good quality FLUKE multimeter, not the one in the bms app to tell you the voltage at the terminals. That kind of thing.

Truthfully, unless your application requires this kind of precision, and no way to prove you are extending life by not having an identical setup treated with different parameters, you'll get on with life using more generalized procedures that avoid the extremes of operation.

Whew - you almost dragged me into a 7 page story about LFP, especially from back in the 2007-2011 timeframe, when it was the wild west with specifications, and most consumers only being used to li-cobalt type batteries. Yeah, that knowledge didn't transfer well.