EVE280 high C rates anyone?

[Dzl]

I'm using nominal as a placeholder in the context of this discussion. It cannot ever in my view describe actual capacity, which you summed up correctly as follows:

See that is what you are missing. You are absolutely correct here (but your correctness is illustrating your misunderstanding of the term). As you said "nominal capacity cannot describe actual capacity" The point of the word nominal is literally to make sure its not confused with "actual" or "technical." Its not meant to be used interchangeably with actual capacity, its not meant to be used in place of actual capacity. Its meant precisely to note "I'm referring to the capacity in the name, not the capacity I actually observed"

If you are looking for a technical specification (and you should be), nominal capacity is not what you want. You want one of two specs:
(1) minimum (rated) capacity (defined in the cell datasheet)
(2) actual or tested capacity (not defined anywhere because it varies cell to cell, and can only be derived through testing / use)

But then you add this:

Which is no help to finding out the actual, minimum rated capacity of a battery.

The minimum rated capacity (not the same as actual capacity) is in the datasheet. If you want to determine minimum rated capacity, just look at the datasheet.

I really think you are getting hung up on a non-issue. Technical specifications are in the datasheet. That is where yo u go for tech spec's like minimum capacity. You will not find actual capacity or nominal capacity in the datasheet (because the former cannot be precisely known without testing or a test report and varies cell to cell and because the latter is not a technical specification, it just means 'named capacity' and is by convention the same as minimum capacity. It is not meant to take the place of more technical or more precise spec's

You say its not helpful to know that minimum capacity and nominal capacity tend to be the same in practice, but I disagree, while you should still verify in the datasheet, the knowledge that cell manufacturers base nominal on minimum means that a cell name is a pretty reliable indicator of the minimum rated capacity. So at a glance, you can get a pretty good indication of what a manufacturer defines as minimum capacity even if you don't have access to a datasheet.

Nominal capacity, by definition, cannot have a set value.

Nominal capacity by definition does have a set value, its just somewhat arbitrary. I think what you mean is it cannot be derived from real world observation/testing, if so you are correct (which is part of what I've been trying to explain).

Rated minimum capacity can and should.

Correct (and does)

 

[Dzl]

Is nominal capacity even a thing? RATED capacity is a thing, and it's listed as a minimum on data sheets.

Not as a technical parameter (at least not to my knowledge). It just means capacity 'of/in the name'. And its something we use in practice for simplicity/convenience, not as a substitute for actual tested capacity.

 

[snoobler]

This is bugging me.

"Nominal" is better thought of as an average for all things. Manufacturing has a "nominal" value for a feature upon which a tolerance is applied, frequently ± some symmetrical value.

Nominal battery voltage is the "working" voltage - used for the purposes of calculations though it rarely applies at any given snapshot in time.

Nominal capacity would only apply to a data set of test results. It would be the practical value for capacity when one has tested and matched their cells to ensure that each cell "element" of a battery has the same "nominal" capacity, which might have nothing to do with RATED capacity.

I'll get over this. I promise.

 

[ArthurEld]

You guys seem to think these sells should be the same as cells you would buy from EVE.
I think you have to give up something for the HUGE discount.
But if you get a bunch of cells replaced I'll get mine replaced too.

 

[Sillyputty]

Nominal capacity by definition does have a set value, its just somewhat arbitrary.

This perfectly describes the nonsense of this issue. Arbitrary cannot, by definition, be a set amount. Your desire to make it so does not.

An analogy: If I want to own a cat (or a lifeop4 battery cell) I can get a cat (or a cell). That nominal description of cat (or lifepo4 cell) has no set specific value. However, once I begin specifying what the parameters of my cat/cell are with any specificity, the nominal description no longer accurately describes what I'm getting.

It still describes what I'm getting, just not the specifics.

I want a short hair cat/bare aluminum cell.
I want the hairless cat/bare cell to be female/have a minimum AH capacity
I want an adult cat/grade A cell

I still think this is simply using nominal incorrectly in this instance. It is something that can and should be used only to describe an overarching group or set of things (batteries, cats, whatever) and that is it. ?‍??

 

[Sillyputty]

You guys seem to think these sells should be the same as cells you would buy from EVE.
I think you have to give up something for the HUGE discount.
But if you get a bunch of cells replaced I'll get mine replaced too.

I really do understand that argument, and agree in this instance (and because of the information shared here by you fine folks) that we will be getting batteries that are likely fudged a bit on the capacity - BUT I know that going in and it's an informed decision.

That's completely separate from trying to figure out what the minimum rated capacity is and holding sellers to that number.

Without those minimum numbers at some point, and earlier rather than later, we'll be trying to dance around and find out if we're getting what we pay for in the future.

We need good reliable numbers to make better decisions. It's a very reasonable expectation.

 

[Dzl]

This is bugging me.

"Nominal" is better thought of as an average for all things. Manufacturing has a "nominal" value for a feature upon which a tolerance is applied, frequently ± some symmetrical value.

Nominal battery voltage is the "working" voltage - used for the purposes of calculations though it rarely applies at any given snapshot in time.

Nominal capacity would only apply to a data set of test results. It would be the practical value for capacity when one has tested and matched their cells to ensure that each cell "element" of a battery has the same "nominal" capacity, which might have nothing to do with RATED capacity.

I'll get over this. I promise.

I think you have correctly identified how the term is used in one specific context, I especially like:

Nominal battery voltage is the "working" voltage - used for the purposes of calculations though it rarely applies at any given snapshot in time.

But if you look at the definition of the word or other contexts in which it is used, It will become clear, you are misunderstanding the meaning and overgeneralizing from one specific example. are misinterpreting that specific example as being broadly representative when it is one example that cannot be generalized from.

Nominal just means 'what we call it' or 'of the name',
Calling a battery cell voltage the average of its voltages makes as much sense as anything,
Calling a battery pack voltage by the commonly used 12v, 24v, 48v terminology is convenient,
Calling a battery capacity the minimum rated capacity makes as much sense as anything,
and calling a PV panel (in the pre MPPT days) by the voltage of the system it is designed to work with arguably makes as much sense as anything (or so they say, this one makes me grumble )

In all cases these are 'nominal' values ('in name' not actual, measured values) but in all cases the nominal value was derived differently in a way that was reasonable to whoever it was that started the convention.

I suppose this illustrates the imprecision and limitation of the term.

So circling back to your earlier example. Nominal does not mean 'average of a range' it means that whoever named the cell voltage decided that the average of the working range was a reasonable name (nominal value).

NOMINAL​

Adjective​

• Of, resembling, relating to, or consisting of a name or names.
• Assigned to or bearing a person's name.
• Existing in name only.

 

[snoobler]

I'm just confused why "nominal" is used anywhere in this thread to apply to capacity. It's not appropriate.

 

[Dzl]

This perfectly describes the nonsense of this issue. Arbitrary cannot, by definition, be a set amount. Your desire to make it so does not.

I feel you and I continuing this discussion will not be productive and at the end of the day we are just arguing over language. I am quite confident in my understanding of the definition and the purpose of the term and am quite frustrated because I am pretty sure you and I would not actually disagree on anything if you took a few steps back and took a bit of time to understand a term that I think I recall you just learned two or three days ago and in my opinion still fundamentally misunderstand (but in fairness I am sure you are frustrated by what you view as a misunderstanding on my part).

For that reason (and because we also now disagree on the term arbitrary, something absolutely can be both set and arbitrary (a mandatory minimum prison sentence, a dollar value for a fine, are examples of arbitrarily derived set values) I think its best just to agree to disagree (and hopefully agree to try to understand the other persons POV a little better).

 

[Dzl]

I'm just confused why "nominal" is used anywhere in this thread to apply to capacity. It's not appropriate.

You are right 'minimum rated capacity' would be a more appropriate term in this instance.

In the case of the EVE cells and all other's I am aware of the nominal capacity is the rated minimum capacity (280Ah) so in practice its one and the same (because the cells by convention are called by their rated capacity, a refreshingly logical naming convention). But I fully agree the more precise language for this topic is 'rated' or 'minimum' capacity.

 

[Pyrofx]

This is turning into schrodinger's cat.

 

[Hedges]

"This horse is glue."

 

[Dzl]

That's completely separate from trying to figure out what the minimum rated capacity is and holding sellers to that number.
Without those minimum numbers at some point, and earlier rather than later, we'll be trying to dance around and find out if we're getting what we pay for in the future.
We need good reliable numbers to make better decisions. It's a very reasonable expectation.

I think one thing that fell through the cracks while we obsessed over wording:

The manufacturer HAS clearly defined minimum rated capacity: 280Ah

many of the things you are seeking clarity on are spelled out in detail in the datasheet if you ever have technical questions about a cell the datasheet is the first and often the last place you look.

 

[hankcurt]

If we define words arbitrarily, our ability to communicate will be nominal.

 

[Sillyputty]

Nominal just means 'what we call it' or 'of the name',

Calling a battery cell voltage the average of its voltages makes as much sense as anything,
Calling a battery pack voltage by the commonly used 12v, 24v, 48v terminology is convenient,
Calling a battery capacity the minimum rated capacity makes as much sense as anything,

??This can be true if a specific number is assigned to it and everyone agrees on that number:

"Calling a battery capacity the minimum rated capacity..."

??This cannot -

"makes as much sense as anything"

The minimum rated capacity of anything cannot be convenient, ambiguous, average, commonplace, or just a placeholder in the sense we are talking about here.

 

[hankcurt]

Actually, the word nominal is super frustrating in kind of a funny way.

Some of the possible definitions are:

1. existing or being something in name or form only (ie. "He's the nominal governor, but has no real power')
2. relating to a designated or theoretical size that may vary from the actual (ie. "The actual diameter of a nominal 1/2 inch pipe varies by material")
3. trifling or Insignificant (ie. "The shipping fee was nominal.")
4. being according to plan (ie. "Altitude is 100,000 feet, thrust nominal.")

So the joke is in the James Bond movie "Moonraker", I always get a laugh when they are first boarding the orbiting space station and somebody says "Oxygen level, nominal." and then everyone pulls ff their space suit helmets. What if he had meant another definition of nominal, like insignificant, or existing in name only? The movie would have ended very differently. I think I would double check what the heck he meant before taking off my helmet.?

 

[Dzl]

??This can be true if a specific number is assigned to it and everyone agrees on that number:

Please review the datasheet. I'm just repeating myself (and I'm just repeating information that is in the datasheet). I truly don't mean to be rude, but I feel you are coming into this discussion with a lot of assumptions, but having done very little research.

Minimum capacity is listed on the second line of the manufacturers datasheet (which I have linked to, screenshotted, and quoted in previous posts).

Minimum capacity, is clearly and explicitly defined in the datasheet, by the manufacturer as 280Ah. That is the specific and agreed upon minimum rated capacity value for this cell. That is the value of the datasheets in general. They establish definitively what a cells parameters should be at a minimum.

 

[Sillyputty]

I think one thing that fell through the cracks while we obsessed over wording:

The manufacturer HAS clearly defined minimum rated capacity: 280Ah

many of the things you are seeking clarity on are spelled out in detail in the datasheet if you ever have technical questions about a cell the datasheet is the first and often the last place you look.

My point here entirely and from the beginning is that when buying a battery or cell, it should be advertised UP FRONT and sold with a clear and unambiguous number showing what that minimum rated capacity is.

A buyer should not be required to delve into data sheets (that one has to request or search for in many instances) to get this data.

That this data isn't OPENLY and IMMEDIATELY available right now is also a given and has been since I've began commenting on it.

I feel you are coming into this discussion with a lot of assumptions, but having done very little research.

Statements that I've missed out on the nuances of what nominal means in this context are beside the point entirely and another discussion altogether.

 

[hankcurt]

@Sillyputty Sorry if it seemed I was poking fun at you or anyone else in the thread. I've just found the communication issues a little entertaining as a casual observer.

I think it is a wise policy to never buy batteries from a vendor until they provide a datasheet for what they are selling. Everything else is just words. The datasheet should also state the test conditions that result in the battery meeting specifications. If the vendor says they are selling batteries that meet the spec, it is proper to hold them to it. If the seller tries to avoid being specific about the minimum capacity of the battery they are selling, then it is buyer beware.

 

[Sillyputty]

@Sillyputty Sorry if it seemed I was poking fun at you or anyone else in the thread. I've just found the communication issues a little entertaining as a casual observer.

I think it is a wise policy to never buy batteries from a vendor until they provide a datasheet for what they are selling. Everything else is just words. The datasheet should also state the test conditions that result in the battery meeting specifications. If the vendor says they are selling batteries that meet the spec, it is proper to hold them to it. If the seller tries to avoid being specific about the minimum capacity of the battery they are selling, then it is buyer beware.

No worries at all. This isn't really about mine or @Dzl's feelings - it's about arriving at an agreed upon definition that meets the requirements of what is specifically being discussed: minimum rated capacity.

Reaching agreement with fellow humans on just about anything can be frustrating as hell! Humor helps!