Battle Born LFP impressions

[PNjunction]

Forgot to mention another mind-blowing aspect, although we've talked about it somewhere along the line..fuel savings with a genny.

So you have a genny onboard to take care of those times when you need to bring your lead-acid up to a full charge. Multiple rainy days - what have you. Typically that is started in the morning up to about 80% SOC, and you let a small solar system take care of that last 20%, because the cost of fuel to run a genny in the CV stage where current is naturally tapering is ridiculously expensive. It takes time. So the small solar setup finishes the job instead.

But with LFP, the charge acceptance is so great, that running the genny up to 95 or even full, (if you've set your CV voltage high enough) can actually be done solely with a genny. CV doesn't take that long, so you aren't incurring a lot of fuel-expense, or perhaps 95% SOC is just fine.

So that's another feather in LFP's hat from a system standpoint. If you do have to use a genny, some of that extra upfront expense is offset by very efficient use of the genny to reach even 100% - which one would never do with lead-acid unless they just want to waste fuel/cash.

I don't want to sound like a marketer trying to keep LFP upfront prices high, but it's just another observation I encountered.

[Mike90250]

The Li BMS does nothing regarding the internal resistance of the cells. New cells = lower IR. So when adding new to the old bank, the new cells take over the brunt of the work, till they are as worn ( Internal Resistance ) as the older cells. No voltage measurement needed, nothing the BMS can do about it.

[PNjunction]

You said it best Mike!

Using batteries with different usage patterns, even if they are the same make/model/capacity, is just not the thing to do.

But people are going to do it anyway and learn the hard way. Or not learn, and just go about putting things together lego-like on a whim. Costly in the long run.

This is why I rail against "one-off" systems built from scraps or other funky DIY methods - they make the poorest choice for making any sort of observations or learning anything truly useful when transitioning to a commercial quality unit.

[tom rickard]

The Li BMS does nothing regarding the internal resistance of the cells. New cells = lower IR. So when adding new to the old bank, the new cells take over the brunt of the work, till they are as worn ( Internal Resistance ) as the older cells. No voltage measurement needed, nothing the BMS can do about it.

I’m not sure how much time you’ve spent measuring the internal resistance of a LiFePO4 cell set.

Your statement sounds good in theory, but i’ve got a $4500 battery analyser that says the internal impedence of a LiFePO4 cell changes with it’s SOCand especially temperature, but doesn’t change with age.

I’d be keen to hear from others, as my cells are only eight years old, so when they start to age things might change..

[Mike90250]

I’m not sure how much time you’ve spent measuring the internal resistance of a LiFePO4 cell set.

Your statement sounds good in theory, but i’ve got a $4500 battery analyser that says the internal impedence of a LiFePO4 cell changes with it’s SOCand especially temperature, but doesn’t change with age.

I’d be keen to hear from others, as my cells are only eight years old, so when they start to age things might change..

Your experience beats my book learning from industry sites. So the user can decide what they want to do (they always do anyway !! ).

[Ampster]

I think that sheds some light on why Lithium is more tolerant of being in parallel.