LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[CatNewBee]

Originally Posted by Cpt Pat

See https://acronyms.thefreedictionary.com/A%2FH

"A/H" is an accepted typographic convention -- not a mathematical formula. You say to-MAY-doe and I say to-MA-doe. Shall we argue about how many angles can dance on the head of pin? Because this isn't an argument -- it's just contradiction.

Sorry, but multiplication and division are exactmathematical terms, it is not amps per hour but amp hours. This has a complete different meaning.

Ampere is a flow and represents already a speed, it is Coulombs per second. Multiplying by time, you get Coulombs alone, the amount of available charges (electrons or positrons) or simply the Capacity. You dont drive miles per hour per hour, do you?

If you want to know how many miles you drive in 5 hours you simply multiply your miles / hour by 5 hours and get the driven miles. Same with the amps.

Please use the correct units, it really hurts people having a clue about electricity.

And accepted by whom btw? We are talking electricity, not religion or gender sciences, where batteries can identify as A/H because they feel so.

[newhaul]

Originally Posted by Cpt Pat

Ah, yes. The ad hominem attack. The last refuge of the defeated debater.

See https://acronyms.thefreedictionary.com/A%2FH

"A/H" is an accepted typographic convention -- not a mathematical formula. You say to-MAY-doe and I say to-MA-doe. Shall we argue about how many angels can dance on the head of pin? Because this isn't an argument -- it's just contradiction.

paging doctor StuM paging doctor StuM
Its Ah not a/h. There is a real measurable difference . Ah is a measure of capacity a/h is a measure of instantaneous usage . Learning this is the hard part for some

Oh and the answer to how many angels can dance on the head of a pin question is however many want to .

[CatNewBee]

Originally Posted by newhaul

paging doctor StuM paging doctor StuM
Its Ah not a/h. There is a real measurable difference . Ah is a measure of capacity a/h is a measure of instantaneous usage . Learning this is the hard part for some

Oh and the answer to how many angels can dance on the head of a pin question is however many want to .

..measure of usage would be Ah/h,
A/h is simply nonsense, like knots per hour.

[john61ct]

3.45V is plenty high to get to true 100% Full from any practical measure of useable energy.

And if held past endAmps, even 3.40V is high enough, even to overcharge, reduce longevity.

Originally Posted by CatNewBee

full cell has a resting voltage around 3.4...3.43V

Depends on the cell, but IME 3.33-3.35V is resting full, after surface charge has been dissipated.

Obviously charging to anywhere near the stressful mfg maximum spec increases the finished voltage, but over time fully resting, it will settle closer to the above.

And the actual usable capacity stored between those two voltage points is insignificant, maybe best expressed in mAh, literally no positive result gained by going that high.

[john61ct]

That Ah vs A/H distinction is certainly true, but is IMO a pretty petty "purity test" and little reflection on credibility when that's already been well established in past posting history.

I've been reading up on identity-based models of belief, biases and glitches in information processing, based on loyalty to the tribe.

Very interesting and I think relevant here.

[CatNewBee]

The resting voltage of the plates is not the same as the charging voltage. To charge a cell means to separate electrons and ions (break the chemical bindings) and move them to the respective plate, where they are repelled by the other electrons ions of the same kind behind the barriere. The force must be high enough to push them over this barriere, otherwise they would spontanously discharge back.

You need a significant force (voltage) to achieve this, it is much higher than the resting voltage. That is the reason why you cannot charge a cell full at the resting voltage. And this is true for all chemistries.

[john61ct]

Yes of course, but nothing there contradicts the above.

Originally Posted by CatNewBee

> That is the reason why you cannot charge a cell full at the resting voltage.

Straw man, no one is claiming you can.

> You need a significant force (voltage) to achieve this, it is much higher than the resting voltage

Depends on **your** meaning of "significant", to the extent the source voltage setpoint is not much higher than the target, that just reduces the current rate.

In Cpt Pat's case that is already very very low, which is why his setup is in much greater danger of overcharging.

If left active long enough, until amps accepted have trailed down to zero, the source setpoint and resulting resting voltage will be very close.

As repeatedly stated, a 3.45V setpoint is more than enough to reach 3.33-3.35V resting. Even 3.40V is high enough, even to overcharge (reduce longevity), it will just take longer.

[Cpt Pat]

Originally Posted by CatNewBee

..measure of usage would be Ah/h,
A/h is simply nonsense, like knots per hour.

Actually, the correct unit for expressing electron flow (current) over a period of time is the "Coulomb." https://en.wikipedia.org/wiki/Ampere_hour

Would everyone prefer to use 3600 coulombs in place of the ampere hour? I didn't think so.

Please resume quibbling...

[john61ct]

Of course in more usual use cases, where current higher than say 0.05C is available, a higher setpoint voltage will indeed result in a faster charge cycle, and most owners would prefer that, and there is no downside to doing so, up to the 0.3-4C ceiling, depending on temperatures.

With a high enough rate, even 3.6Vpc would be fine for a CC-only profile, or one where the Absorb Hold Time does not result in a resting voltage result much higher than say 3.4V, very little surface charge.

[newhaul]

Originally Posted by john61ct

Of course in more usual use cases, where current higher than say 0.05C is available, a higher setpoint voltage will indeed result in a faster charge cycle, and most owners would prefer that, and there is no downside to doing so, up to the 0.3-4C ceiling, depending on temperatures.

With a high enough rate, even 3.6Vpc would be fine for a CC-only profile, or one where the Absorb Hold Time does not result in a resting voltage result much higher than say 3.4V, very little surface charge.

so let me get this correct you are saying holding a charge of 3.45vpc at a constant daily .1C will be detrimental to an Lfp bank
I have been doing just this well over a year with 0 loss of capacity. On solar
It seems that real world trumps laboratory bench theory.
Will my bank die prematurely who knows . We are all operating in uncharted territory wrt liveaboards using Lfp house banks. What is the life expectancy? Nobody really knows ( wrt our usages)
who really cares if it only lasts 10 years instead of 11 years. By the time I have to replace the bank under this scenario the price will be even lower than the 3 bucks per 12v Ah I spent this time.

[Cpt Pat]

Henceforth, I will use only the term "ampere hour" (sans contentious abbreviations) in this thread to squelch the anal retentives who are generating noise by having nothing better to contribute.

[john61ct]

Originally Posted by newhaul

so let me get this correct you are saying holding a charge of 3.45vpc at a constant daily .1C will be detrimental to an Lfp bank

Not if SoC is regularly being brought below 100%SoC.

And the real danger from lower charge rates really only starts being an issue well below 0.1C

Of course cycles are only lost off the back end of lifespan, the impact of factors like this would not be detectable over a short time period like a year or two.

[john61ct]

Originally Posted by Cpt Pat

contentious abbreviations

AH or Ah are not in any way contentious. I agree that it is silly to treat variations as any more than a convenient label for the standard unit "amp hour"

Certainly nothing to do with maths, any more than "amp-hour" represents subtraction.

[Cpt Pat]

Originally Posted by john61ct

AH or Ah are not in any way contentious. I agree that it is silly to treat variations as any more than a convenient label for the standard unit "amp hour"

Certainly nothing to do with maths, any more than "amp-hour" represents subtraction.

Thanks, John. But there are people here who lack the cognitive ability to distinguish between an abbreviation and a math formula (hint: it depends on context). You and I both know that "amp-hours" doesn't mean: "amperes minus hours." But in the interest of reducing the noise, I'll avoid using any abbreviations for ampere hours -- and I'll restrain myself from pointed out we are all technically wrong for not using "coulombs." "Ampere hours" is a non-scientific term used only by convention.

If I really wanted to be anal about it, I'd reference everything to coulombs.

[john61ct]

These are actually pretty rare units, native metric, apparently no USA-imperial equivalent!