Lithium batteries - true longitudinal capacity profiles?

[avanti]

Originally Posted by Davydd

You said "above message" not "messages".

As a matter of fact, I didn't:

Originally Posted by avanti

I became confused at least three times in the above messages alone.

my battery manufacture doesn't mention watts nor do most other 12v battery manufacturers

LMGTFY:

First hit:
https://www.lithionbattery.com/wp-co...eet-210623.pdf

which says:

ENERGY -- 1.84 kWh

[emphasis added]

If you care to offer an even more picayune argument, please carry on. I'm out.

[Davydd]

Are you accusing me and most others as being picayune (small and petty) referring to amp hours? If i refer to amp hours, tough. You can do the translation math to understand what I am saying with your new found condescending knowledge even you hadn't expressed in the past. If you are out as you say, try to stick to it.

[GeorgeRa]

To continue Avanti’s point regarding battery description, a single number will not serve all battery calculation needs, it is like describing a car – a thing which has five wheels, practically all do but try to get new tires.

Voltage – necessary to size appliances
Ah – wire sizing, how long can you run appliances at correct voltage
W – a unit of power, oomph, can you run 1000W heater or just 100W PC charger
Wh - unit of energy, how long will your battery last providing power “X” at given voltage

This manufacturer, link from Avanti has many numbers and all are usefull, so driving to a single unit is just senseless.

[booster]

Amp-hours and watt hours aren't exactly interchangeable without the voltage so both can be used if the voltage is given for amp hours, but voltage is still needed to know what is going on with the stated item if given in watt hours. But at least they are both energy terms.



Amps and amp hours aren't interchangeable either, but they also are not terms for same thing so much different and more confusing, especially for normal non techy folks looking at battery systems specs. There is really zero justification in using them interchangeably. The marketing folks just started doing that to make their products look more competitive with total disregard of the how it would affect their customers after the purchase when they discovered they didn't get what they thought they were getting.


At about the same time as Roadtrek started using them interchangeably, they also did less than up and up change to their fresh water capacity spec to not be the standard tank capacity. They started including the water in water heater even though that is unusable water. Same deal as with the batteries and only done to make the system look bigger than it really was.



RV specs are full of stuff like this so it gets really hard for customers to sort through it all unless they are very experienced and knowledgeable. Remember that etrek claims of "run the AC all night and recharge with the engine generator in 20 minutes"?

[avanti]

I agree with everything that George and Booster said. My original point, though, is really a very simple one:
If you want to compare how "powerful" two batteries are (i.e., for example, how many hours you can run your A/C, or how many cups of coffee you can brew), the simplest number that you can use for your comparison is the "watt/hour". It is true that you can also use amp/hour/volt, but that is just another way of saying "watt/hour" but with more numbers.

It is as simple as that. One upfitter may choose to use 12V batteries, another may pick 24V or 48V, and a third may use 6V batteries in series. In comparing such systems, none of this matters--just add up the watt/hours and you can do a direct comparison. The equivalent comparison (across many rigs) using amp/hours would be a nightmare.

As George says, there are many other questions one might ask, but my claim is that "how powerful?" is by far the most common one in casual discussions. For this purpose, the watt/hour is both most correct and most understandable.

Just sayin'...

P.S. -- I should have known better than to raise this in an existing thread. At OP's request, I would be glad to move it all to a separate thread, if she prefers.

[Urlauber]

Sorry, but watt/hour doesn't make sense. It is watt*hour, or watt hours. Maybe you "mean" that, but it's just wrong mathematically and would cause even more confusion. 😏

[avanti]

Originally Posted by Urlauber

Sorry, but watt/hour doesn't make sense. It is watt*hour, or watt hours. Maybe you "mean" that, but it's just wrong mathematically and would cause even more confusion. ��

Fair enough. Obviously, I never intended it to mean "watts divided by hours". The underlying concept is actually "watts per hour" (or at least that is close) and forward-slash is often used to mean "per". But you are right--it is confusing and "watt-hours" (or just Wh) is preferred for that reason.
Won't happen again.

P.S. -- As a fun fact, the watt-hour is actually a measure of energy, but is not actually a sanctioned SI unit. If we wanted to be all sciency, we would use the SI unit "joule" instead of Wh. That wouldn't make anybody happy, though.

[GeorgeRa]

I noticed good progress, not so long ago some of us equated battery capacity in Amps or Amphours. The Amps unit is going away on this forum, that is advancement.

[MsNomer]

"The underlying concept is actually "watts per hour" (or at least that is close)"

No, it's watts times hours.

[Snowy]

Originally Posted by GeorgeRa

Voltage – necessary to size appliances
Ah – wire sizing, how long can you run appliances at correct voltage
W – a unit of power, oomph, can you run 1000W heater or just 100W PC charger
Wh - unit of energy, how long will your battery last providing power “X” at given voltage

I think everyone here kinda understands the physics, that V*A=W. But look at all the confusion we write. As MsNomer writes, it is Wh, not W/h. GeorgeRa wrote that wires are sized by Ah, but that is not true, it is just amps.

There was a time when everything was 12v so using Ah for power was an acceptable and widely used surrogate for power. Many still use it and their lives go on just fine. But things are changing, and higher voltage systems (and subsystems) will become more common because higher voltages have advantages.

But this is a forum where we are trying to convey accurate information in a consistent way. I think the proper units should be, after GeorgeRA:

Voltage (V) – necessary to size components of the system
Amps (A) – wire sizing - more A requires bigger (heavier) wires.
Watts (W) – a unit of power, oomph, can you run 1000W heater or just 100W PC charger
Watt hour (Wh) - unit of energy, how long will your battery last providing power W.

[avanti]

+1 @snowy. Very well put.

[I wish this forum had a "Like" button.]

[booster]

Originally Posted by avanti

+1 @snowy. Very well put.

[I wish this forum had a "Like" button.]

I agree. It would be nice if some parts of this discussion showed up on a sticky so, especially new users, could be referred to it.

[GeorgeRa]

Originally Posted by Snowy

I think everyone here kinda understands the physics, that V*A=W. But look at all the confusion we write. As MsNomer writes, it is Wh, not W/h. GeorgeRa wrote that wires are sized by Ah, but that is not true, it is just amps.

Thank you for your post and thank you for correction, my typo. Indeed, wire conductors must be sized by current measured in Amps. Wire ampacity, current conducting ability, is directly proportional to conductor size.

[InterBlog]

Originally Posted by avanti

…. I should have known better than to raise this in an existing thread. At OP's request, I would be glad to move it all to a separate thread, if she prefers.

In an indirect way, all this could actually be germane to the issue of lithium life loss (we need to name this emerging phenomenon and I’m considering L-cubed or L3).

Not discussed thus far is the extent to which L3 wreaks havoc on the reliability of the output displayed by the BMS that was calibrated to the original nominal capacity. Or perhaps just some BMSs, depending on their programming - I don’t understand the scope of what I’m trying to express just yet, but let me introduce this aspect anyway.

To make a long story short, I don’t want to turn my van into an academic hobby. The whole point is to USE THE VAN, and aside from cursory monitoring, the electrical system is supposed to take care of itself without a lot of mental gymnastics required of me. A good electrical system is mostly “set it and forget it”.

That being the case, I have largely ignored the individual cell voltage measurements and the other avalanche of data that the Electrodacus generates in favor of that one magic number displayed in the biggest, most convenient font - the percent SOC.

L3 destroys the accuracy of the percent SOC readout, and recalibrating it to the reduced effective battery capacity is not as easy as theory suggests. The drift is somehow far larger than what my intuition says it should be, leading to the following maddening result: Right at the point where my reduced battery capacity requires me to monitor the SOC more closely than ever, my ability to do so is thwarted.

So, OK, life sucks and then you die, but until that time, you develop workarounds.

Initially, I stuck a piece of masking tape on the control panel reminding myself to charge to 13.6 irrespective of what SOC the BMS says the battery is at, which I found reminiscent of what astronaut Jack Swigert did during Apollo 13 - a $2 billion spacecraft that, analogous to my battery, did not survive first contact with the enemy that nobody comprehended until it manifested. And so he used a note taped onto his control panel in partial compensation for the failures he was coping with.

But even with that alternate administrative control, I still wasn’t able to recalibrate my feel for SOC because guess what?? There is not a linear correlation between voltage and SOC. I told my husband that a “charge to” reminder was not enough - if the BMS itself cannot give me a feel for the degraded-battery SOC in real time, then I need a cheat sheet, an XY graph that plots voltage against actual SOC to the best of our ability to determine it, because it will be awhile before we can replace this battery to the effect that we will no longer need to worry about eking out power at the margins. He’s in the process of making individual measurements for that right now, and it’s clearly not linear.

All this is to say - HOW SHOULD these things be designed to account for the inevitable L3? Amp hours, watt hours, voltages,… some of these power-related claims reflect marketing obscurations on top of the technical obscurations that every LFP owner is probably going to face sooner or later. I don’t have a feel for any of this yet, for what should happen or how things should be designed to make things easier for the end user. I’m just throwing this bit onto the thread.

[booster]

I think that you could possible do a couple of things to help lifespan based on my, so far, limited testing of our 618ah bank of 3 SOK batteries.


I did all the preliminary "charge the batteries up to equal voltage" so they equally will share load type stuff that they recommend, including taking them to 14.5v to get them to balance the cells.


I installed them and did a capacity test and it was horribly low. When I looked at the cell balance it was horrible also. I had to leave it at 14.5v for a long time with it cycling off the high cell voltage trip in the BMS and doing tiny balancing steps in between. Cell balance was much better and they then met capacity.


The issue was the cell balance and even on new cells it knocked the capacity hard.



There is a very good reason this happens and it is the way the BMSs are designed, although that design may be the only practical way to do it.


The high and low voltage limits, which are the reference points for the capacity test trip, trip off any given cell going above/below them. If the cell voltages are unbalanced the BMS will trip when the highest cell hits the high limit and when the lowest voltage cell hits the low limit, no matter how much capacity is still in the other cells.


It would be interesting to see what your cell balance is as you said, I think, that you have an active balancer on your bank.


If you have a balancer that works well and you still have a bad cell or two, you will lose as much tested capacity as it all the cells were bad.



I think this is the reason we see so many "refurbished" batteries for sale. The batteries got a bad cell or two and got scrapped out but the remaining cells are still good, most likely. The rebuilders sort them out by actual capacity and put them into the refurbished battery. Makes total sense because the cells themselves appear not to be repairable, but many batteries are being repaired.


Battleborn and SOK have the kind of cheesy automatic balancing that they want to do on every charge cycle, but they don't activate it until 14.4v so you have to violate the "don't charge to total full all the time" lithium rule to do it.


Another thing I found was that, contrary to what the literature says, you need to hold the voltage at whatever charge voltage you go to, except total full at 14.7v, to get as much capacity in them as possible at that voltage. Basically, you require the absorption time that the lithium folks tell you isn't needed. I have been charging to 13.8v and the hold time is quite a while, but I haven't measured it accurately. Maybe as much as an hour. According to an academic white paper I read, they call that "saturating" the charge at that voltage and recommended it. They also said that the best way to do that saturation is to stop the charge based on amps getting to near zero. Sounding more and more like AGM every day, huh. My shore charger can charge like that in CC/CV mode and I have it set to kick out at 3 amps for our 618ah bank.



If you aren't holding at 13.6v for a time, you probably won't get get full capacity and perhaps the hold time gets longer as the batteries age. You may want to take a look at the charging amps to the batteries when the it your set 13.6v. Our bank was still accepting over 30 amps when we hit 13.8v.


You may want to turn off the balancer and watch what happens to the cell balance over a couple of cycles. If some cells are reading low all/most of the time, that could be and issue, I think. Also let the batteries sit for a while with the balancer off and see what the cell voltages do.

[@Michael]

Originally Posted by InterBlog

Initially, I stuck a piece of masking tape on the control panel reminding myself to charge to 13.6 irrespective of what SOC the BMS says the battery is at,

Is that voltage high enough to enable the cell balancer in the Electrodacus?

Originally Posted by booster

The issue was the cell balance and even on new cells it knocked the capacity hard.

That's worth looking into in this case. It's possible that there's a bad cell.

If I were in this situation, I'd verify cell balance and try to correct cell balance, and if the pack still had reduced capacity, I'd reset the SOC meter to the measured battery capacity, rather than rely on voltage to infer SOC.

[InterBlog]

Originally Posted by booster

…
…
It would be interesting to see what your cell balance is as you said, I think, that you have an active balancer on your bank.

….

Cell balance is captured by the image in my post above, although I never pointed it out except with tiny red arrows, so I’ve re-emphasized it with white markups in this screenshot below: Four cells all showing voltage consistency to the thousandths decimal place. The BMS home screen provides a numerical read-out in volts but also a handy bar graph that provides a visual short-cut to the right (due to the way the system was wired up, our 4 cells are numbered 1, 2, 7, and 8… this BMS has the capacity for 8 cells but we configured 4).

As far as we can tell, we have never had any laggards. IIRC, cell balancing is supposed to be the thing that the Electrodacus does best. Several years ago when it was developed, the prevailing narrative themes were different and balancing was talked about largely in the safety context, rather than in the longevity context.

[booster]

Originally Posted by InterBlog

Cell balance is captured by the image in my post above, although I never pointed it out except with tiny red arrows, so I’ve re-emphasized it with white markups in this screenshot below: Four cells all showing voltage consistency to the thousandths decimal place. The BMS home screen provides a numerical read-out in volts but also a handy bar graph that provides a visual short-cut to the right (due to the way the system was wired up, our 4 cells are numbered 1, 2, 7, and 8… this BMS has the capacity for 8 cells but we configured 4).

As far as we can tell, we have never had any laggards. IIRC, cell balancing is supposed to be the thing that the Electrodacus does best. Several years ago when it was developed, the prevailing narrative themes were different and balancing was talked about largely in the safety context, rather than in the longevity context.

That balance looks good, but the question would have to be how you got 300ah on 4 cells.


I have to assume you have a parallel then series setup or a series then parallel system?


If you do have more than 4 individual cells, you can easily have cells hidden within them that are bad, but group still looks OK.


If you have access, it would be interesting to measure the individual cell voltages to see what you have on them. You need a .001v resolution meter to do it as the much more common meters can't read that accurately. The bad is that any parallel groups have to be isolated each other and rested before you can do that so it can be a lot of work to do.


I don't know how your BMS works, but it would probably only be able to balance the series strings as it wouldn't be able to see bad cells that are in parallel with good ones most likely.

[avanti]

Originally Posted by InterBlog

To make a long story short, I don’t want to turn my van into an academic hobby. The whole point is to USE THE VAN, and aside from cursory monitoring, the electrical system is supposed to take care of itself without a lot of mental gymnastics required of me. A good electrical system is mostly “set it and forget it”.
[...]
All this is to say - HOW SHOULD these things be designed to account for the inevitable L3?
[...]
I don’t have a feel for any of this yet, for what should happen or how things should be designed to make things easier for the end user.

These comments really resonate with me. I can be pretty passionate about getting things "right", but I am neither well-equipped or very interested in repeatedly following complicated regimens for the sake of some machine.

I also don't have much of a feel yet for the complexities of my new power system. I am happy to learn what it takes to answer your "HOW SHOULD..." question, and am fairly good at it. What I am NOT good at is remembering and following the kind of minutiae that is necessary to do the right thing consistently.

This is why I am so enthusiastic about automation in general and Home Assistant in particular. Some people seem to think I am motivated by the search for a science experiment, but this isn't true. What I get excited about is the prospect of coming to understand best practice, embodying it in detailed automation rules, and then being able to forget about the details.

As a very simple example, I know that lithium batteries are happiest being stored at a mid-level charge. But during a trip, I am happiest with a fully-charged battery. So, I plan to have a "going home" switch on the dash that will tell the system which mode I desire. The presence of the switch will save me from remembering the target SOC and having to monitor it. This is a trivial example, but there are many others. My Victron setup is deeply integrated with Home Assistant--it exposes literally hundreds of parameters, most of which I don't understand and won't remember even when I do. By using these parameters in rules that are more sophisticated than simple SOC rules-of-thumb, and by automatically tracking the drift of parameters as the batteries age, I expect to be able to optimize the system's behavior without turning my vacation into an "academic hobby".

[booster]

Originally Posted by avanti

These comments really resonate with me. I can be pretty passionate about getting things "right", but I am neither well-equipped or very interested in repeatedly following complicated regimens for the sake of some machine.

I also don't have much of a feel yet for the complexities of my new power system. I am happy to learn what it takes to answer your "HOW SHOULD..." question, and am fairly good at it. What I am NOT good at is remembering and following the kind of minutiae that is necessary to do the right thing consistently.

This is why I am so enthusiastic about automation in general and Home Assistant in particular. Some people seem to think I am motivated by the search for a science experiment, but this isn't true. What I get excited about is the prospect of coming to understand best practice, embodying it in detailed automation rules, and then being able to forget about the details.

As a very simple example, I know that lithium batteries are happiest being stored at a mid-level charge. But during a trip, I am happiest with a fully-charged battery. So, I plan to have a "going home" switch on the dash that will tell the system which mode I desire. The presence of the switch will save me from remembering the target SOC and having to monitor it. This is a trivial example, but there are many others. My Victron setup is deeply integrated with Home Assistant--it exposes literally hundreds of parameters, most of which I don't understand and won't remember even when I do. By using these parameters in rules that are more sophisticated than simple SOC rules-of-thumb, and by automatically tracking the drift of parameters as the batteries age, I expect to be able to optimize the system's behavior without turning my vacation into an "academic hobby".

How are you defining "full"? At max charge for lithium at 14.7v rested for a 12v system, or with some % headspace on the charge?