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john61ct · 09-10-2018, 04:44

Quote:

Originally Posted by 200MPH

the battery supplier also supplied the LFP specific chargers, which more or less match the info printed on the side of the batteries

yes the vendor / industry spec'd voltages are **always** too high wrt optimizing for longevity. That is not their priority goal.

jkleins · 09-10-2018, 06:34

Quote:

Originally Posted by john61ct

yes the vendor / industry spec'd voltages are **always** too high wrt optimizing for longevity. That is not their priority goal.

So what is their goal? Why would a vendor/industry spec a voltage that was clearly detrimental to their product unless they had some other purpose like performance, utility, what?

john61ct · 09-10-2018, 06:55

Quote:

Originally Posted by Delfin

Your words are not being misrepresented

I have actually edited my summary boilerplate text on that sub-topic several times, what you quoted above is from an older version. But in reality, the only change is greater precision in the caveats.

________
Store at a low SoC. "Not over 50-60%" say most, to compensate for self-discharge, if not getting topped up regularly (I would at least monthly).

"Lower the better" say many more recently, as long as you take **zero chances** letting self-discharge drop below 10-20% SoC, certainly not below 3Vpc.

Isolated from everything including your BMS and cooler the better.

john61ct · 09-10-2018, 07:02

Quote:

Originally Posted by jkleins

So what is their goal? Why would a vendor/industry spec a voltage that was clearly detrimental to their product unless they had some other purpose like performance, utility, what?

Well obviously their **primary** goal is to maximize their profits, selling lots of batteries means simplifying things so people think it's OK to use their existing infrastructure designed for lead.

Also smart vendors think long term, and how smart would it be to teach your customers how to make your product last for many decades?

The auto industry could easily have developed utilitarian cars and*parts*supply chains, so that consumers could routinely drive them for 50-100 years. For purely rational free-market economic reasons, that has never happened.

But setting such "conspiracy" ideas aside, the vendors' focus is on their 99.999% main customers, the military and EV propulsion, where range/per-use capacity is everything and expected lifespan is short anyway.

EV's high C-rate usage is **very** different from our much gentler House bank cycling. Note also that most EV people talking "lithium-ion", mean other chemistries not as safe as LFP, much shorter lifetimes, and with completely different setpoints and behaviors.

Gentler House bank*storage*use cases are .001% of the cell manufacturer's market, so therefore no testing / different specs are developed for that use case; that has been left to the end users, and the more objective/technical vendors like*Maine*Sail.

So, following those vendor charge specs is fine **if** you only want the cycle lifetimes they advertise.

You can however, get **much** longer life by "avoiding the shoulders": look at the SoC vs Voltage chart, and avoid the "shoulders" at both ends, stay in the smooth parts of the curve.

Delfin · 09-10-2018, 07:19

Quote:

Originally Posted by jkleins

So what is their goal? Why would a vendor/industry spec a voltage that was clearly detrimental to their product unless they had some other purpose like performance, utility, what?

I believe the theory is that LFP manufacturers have discovered a novel way to increase profits - disappoint their customers so they will come back to be disappointed again. Same reason why Japanese and German car manufacturers couldn't take market share with superior, longer lasting products than the crap being produced in America in the 70s, and why restaurants that serve lousy food at high prices prosper, while those serving great food cheaper all go out of business. Clear?

GaryBode · 14-10-2018, 12:34

Look at the self-discharge rate of the LFP battery. You don't need to float. Do whatever the manufacturer recommends.

tanglewood · 14-10-2018, 13:22

Quote:

Originally Posted by GaryBode

Look at the self-discharge rate of the LFP battery. You don't need to float. Do whatever the manufacturer recommends.

It's not about maintaining the battery's charge level, but rather about powering loads with the shore charger or solar when available. Programming the "float" function in a charger to match the battery's resting voltage accomplishes this without continuing to charge the battery. It's an alternative to disconnecting LFP.

travellerw · 14-10-2018, 13:32

Quote:

Originally Posted by tanglewood

It's not about maintaining the battery's charge level, but rather about powering loads with the shore charger or solar when available. Programming the "float" function in a charger to match the battery's resting voltage accomplishes this without continuing to charge the battery. It's an alternative to disconnecting LFP.

Careful with responding to this user.. His last few posts seem very strange.