Parallel "Groups" or Parallel Strings or Neither ?

[eMark]

16s4p was just an example, im jumping upto 17s4p, the batteries iam using right now are 2-14s4p in parallel wired with a removable 14s 25amp bms I use for charging.

Whether 13s, 14s, 17s, etc if only two or four + series runs the length of the pack does not lend itself to positioning the idle 14S balance leads of a BMS or positioning the 14 balance leads for true balance charging. Your wiring description with 8 series strings (4-positive) is less than ideal for fuse wiring and less than ideal for BMS balance leads or balance charging leads. For fuse wiring you need only 2 positive series strings running lengthwise if fuse wires were your only means of pack cell protection (besides the pack fuse).

I play with different battery sizes so my 13s batteries have bms, 14s yes but not when on my bike, 2-15s5p I never balanced charged and after 3000km they were still balanced.

An indication that you aren't abusing your two packs and more likely doing only a 85%-95% charge the majority of time and only a 35%-50% discharge the majority of time. Not sure what you mean by different battery(cell) sizes? Seems like it's just a matter of time before your pack of different battery sizes (mAh capacity) becomes more and more unbalanced with pack cells having different capacities (e.g. possibly as much as + - 50-70mAh high/low variance from the combined 14S4P pack cell mAh average of the 56 cells).

My 14s4p have 4-14g positive wires and 4-14g negative wires coming off the pack/ 1 for each P so I pull current straight through pack. then it all gets soldered into 1 positive and 1 negative

So it sounds like your pack series runs are lengthwise instead of crosswise like this 14S4P pack ... https://i.imgur.com/KPNtKSB.jpg ... https://i.imgur.com/KT4ZbUd.jpg (when i say pack fuse i'm referring to the fuse on the red wire). According to your pack wiring the 4P cells makeup the series strings. That was why i started this thread and as spinningmagnets corrected another member that parallel cells are not always in a "group" but sometimes in a "string". According to your pack description the 4 parallelled strings are connected at the ends making them in affect 4 paralleled series strings. From your description your 4 series runs are lengthwise instead of the 7 series crosswise runs like in those two 14S4P photos? These packs are by EbikeAus ... http://endless-sphere.com/forums/viewtopic.php?f=14&t=93297&sid=27077d11fcc5c01fa46ffc50b82b1240

So when you talk about fusing a battery, what im hearing you say is on a 4p battery you would use two fuses going from 1s to 2s and you would place the fuses in between the 1p and 2p going to the 2s then 3p and 4p going to 2s. and if that is the case I could use only 2 positive wires and 2 negative wires coming off the battery but heavier gauge.

Those two photos should help explain how to run your series strings with the provision for attaching the idle balance leads of a BMS and/or attaching balance leads for true balance charging ... https://i.imgur.com/KPNtKSB.jpg ... https://i.imgur.com/KT4ZbUd.jpg

At first got the impression you were running only two series strings the length of the battery with one P-cell of the 4P on each side of the two strings. That arrangement calls for fuse wiring (IMO) when you don't properly incorporate a BMS or provision for properly running the series runs for attaching either the idle BMS balance leads or the balance leads for true balance charging.

I'm curious how to protect battery pack A from battery pack B(paralleled) without using a bms while on the bike.

If each of your packs has the same cells and each pack when balance charged has the same Ah capacity shouldn't be a problem; especially if each cell is fuse wired for added protection. Being as you say, "I never balanced charged and after 3000km they were still balanced" then why even parallel them together? Just switch over to the other pack when the first one is discharged to (say) 35%. You may even have a watt meter to keep an eye on while riding?

I did what I considered a bottom balance. when these cells were in a 2-14s5p with 2 bms wired I took all cells to 3.0v then I parallel charged both packs through a watt meter for 13 or 14 hours? at 2 amps 58.8 and the watt meter said 27ah. cant really remember exactly maybe the bms burned off 2 ah of the 25r packs but the meter said 27ah.

You bottom balance charging is actually discharging, by balance charging i meant until each cell is the same voltage as the highest cell (e.g. 3.2-3.4v until all cells are at 3.4v). It takes forever with a BMS to idle discharge balance. The primary reason i decided to go with a Vruzend kit is for experimenting with cell arrangement, occasionally using a balance charger (when needed), as well as being able to check individual cell voltages with a DMM when necessary.

So my next build will be 2-17s4p and if I like it ill buy a couple bms. then ill worry about getting new higher quality batteries

If you can get 3000km and your pack(s) have never been bottom balance charged i'd say your previous source for acquiring relatively inexpensive used cells is GOOD ENUF!

 

[methods]

Ok, I found some time to come back to this.

Of course, the only thing I said... is that if you want help from experts... breaking up text with pictures helps. This is because there is a lot of noise and very little signal (at times) on the forums and skimming for pictures is what a lot of folks do.

...

Now, on to the first response.
I see 4 pages after this and I only have 5 minutes.

Don't mean to be disrespectful, but it would be helpful if methods would not make light of this Series/Parallel discussion as if he has all the answers. Perhaps, methods can explain why most all triangular packs have just one Series String; whereas most rectangular packs have two or more paralleled Series Strings (maybe by his third cup of joe), but don't hold your breath :wink: .

Read my post again.
I am an expert in forum posting (that will result in help from experts) even if you believe (for some reason) that I am not an expert in wiring batteries.

The second half of your question is effectively a non sequitur.
What are you even saying?
You either have no idea what you are talking about or you are trying to inflame.

The shape of a pack has absolutely nothing to do with the number of cells in series (which drives sum voltage) and the number of cells in parallel (which drives sum capacity) - and both of those - are well below the topic of discussion which I believed to be the nuance of whether you parallel first, then series those parallel groups or whether you series first, and then parallel those groups.... a topic which... once you understand Ohms Law and battery balancing... becomes a moot point due to the necessity to be able to balance cells individually (where a cell can be 1 pouch or can, or many pouches or cans in parallel, BUT NOT SERIES)

Perhaps method can also expound upon the rationale and further enlighten us on spinningmagnets post ...

This might be a good time to mention something. It has been widely embraced to parallel cells first, and then connect those paralleled cells in series to finalize the pack size and shape. ... I now believe there is less line resistance if the cells are connected in series first. This may cause the pack-building to be more fussy and time-consuming, but it might be worthwhile for some builds...

Nothing he is saying registers as grossly non-factual.
I am far less concerned with inline resistance than with the basic concept... so... we need folks to understand the difference between two cells in series and two cells in parallel

(Which I think you still may not get - hence your shite attitude?)

It works out to Ohms Law and the like.
It is a rule of physics that voltages in parallel MUST be equal
It is a rule of physics that currents in series MUST be equal

By these laws, it becomes apparent, that you can treat multiple cells in parallel as if they were a single cell.

Similarly
You can not treat two cells in series as if they were a single cell. There are many proofs to this, one being, that if the two cells are at a different state of charge, when a charge session begins, then the cell with the higher state of charge will over-charge before the cell at a lower state of charge becomes full.

Another proof is that you can only read the sum of voltages and not the individual voltage, so if the cells are of a slightly different capacity you will fail

Another proof is that it does not scale... if you run 40 cells in series and only look at the top and bottom of the pack you have failed.

... The best lens to view this thru is assuming you are starting with a pack of shit-cells. Random cells at random states of charge with random capacity. In doing this exercise it will quickly become apparent that paralleling first and then running those parallel groups in series ALWAYS WORKS... and that running in Series Only (with no center taps) or running Series and then parallel (with no center taps) introduces single point failure mechanisms which are undetectable.

Anyone who is even marginally competent or experienced knows that for a professional application, cells resting at the same level in the pack, must be electrically paralleled.

... It is acknowledged that myself and others often break this rule with Hobby Packs. This results in random cell fatigue, early failure, and can be considered "Accelerated Aging". ... i.e. A proof to the need for proper pack building and a BMS.

And of course - I sell BMS's

TIME
(and note to self never to answer one of his posts again)

-methods

 

[methods]

The problem with putting series strings together in parallel with only small gauge parallel connections at the cell level is, what happens when one cell in the pack is weak or is dead. ie high current will try to pass through small wires. Other than maybe some of those handmade Chinese packs that so commonly fail, no manufacturer in the world makes battery packs that way...for good reason.

That is a guy with a lot of practical experience.

-methods

 

[methods]

True,
His questions are not making sense because he understands some of it, does not understand some basics, and has a flippant attitude. I am sure he will come around after a few months of reading when it all makes sense.

It is all rules of physics, laws of electricity, calculable facts, and experimental proofs. There are no Opinions in this, unless someone is guessing or projecting... and around here... we have beat all of this to death a thousand times over with field test...

A quick search will show you who has been doing this for years, how they failed, how they had success, what they understand, what they dont.

-methods

You are trying so hard to impress others with your head knowledge that it gets a little old; especially when you have to demean and discredit someone along the way. Lighten up and don't take a little humor once in awhile as a personal attack (e.g. Plz Xpln).

Not at all.

My point is it is impossible to understand your questions

therefore impossible to help you understand how this stuff works

But I'm happy to give up, obviously communication's just not happening same bizarre phrases just getting repeated.

I'm honestly just trying to help.

Best of luck, maybe on other topics things will click.

 

[methods]

https://endless-sphere.com/forums/download/file.php?id=262218

Any idea why three colours are used there, what they are supposed to represent?

Rasta?



-methods

 

[methods]

Yea... that one made my head spin and I ran outside screaming...

and... the talk of "belief" - eh...
In Electrical Engineering there is not debate.

There is Fact and Rational
There are multiple "best ways" and they resolve to the definition of Success.

One person's definition of success is the cheapest pack build
One person's definition of success is the fastest pack build
One person's definition of success is the most reliable pack build
Another person (most people) just build with what they have.

... In logic and proofs
The fact that something has not yet failed, is not a proof that it works.

This is a common misconception on forms. Since forums have many non-scientists, often times, anecdotal data is collected that... for the most part... proves out "true enough" - but - strictly speaking - many times logic that is used is not sound.

... skimming posts and responding

-methods

Note taht I am replying to each of the replies above that has misconceptions, so I can be sure the correct information is being passed along.

There are multiple concepts being discussed in this thread, and some of them are being confused with each other.

So, if the pack is instead built using parallel groups of cells wired in series (the common way to build packs), balancing is easy, only needing one BMS, balancer, or RC charger. Same thing with monitoring LVC.

In other words the preferred build for a triangular pack is with one central Series String being fed by Parallel Groups ... https://endless-sphere.com/forums/download/file.php?id=262218 for making the best use of the smart BMS, for pack safety, performance and cycle life longevity.

No.

There is no "central" string of any kind.

What you have, in any pack, that is built of seriesed sets of parallel cells (necessary if you wish to use a single BMS or other monitoring/protection system), is exactly that: seriesed sets of paralleled cells.

*How* you series them is completely irrelevant to this. (though it may be relevant to how current flows thru the system, if it's high enough)

You're applying one choice in pack building (whether to series parallel groups, or to parallel independent series strings) to a completely different part of pack building (how to series the parallel groups).

 

[methods]

In practice we dont see this much (where dead cells get hooked together with fully charged cells) - but you may be talking about something different. I have personally measured these currents, and if you do the same, using a scope and a Fluke, you may be surprised. It is ... eh... pretty uneventful at low potentials. For cells that are even relatively similar, I don't even think about it. It is like 300mV of potential and the currents that flo will hardly show up on your meter. Proofs can be made even in the absence of metering, but back-calculating any proposed impulse currents that flow at the time of connection. You will find... that hooking a fully charged battery to a half charged battery "for a second" will NOT result in a significant transfer of charge, and therefore, there is not a significant current flowing. ... Whether there are any damages to the electrodes... that is stuff that LFP can talk about. My job is to thrash the batteries, not make them last longer

...

My experience has been that packs are manufactured with new cells of similar charge.
Packs are built up in hard-wired parallel groups, then those are put together into series... look for pics of the Tesla modules
(technically they are all on a sheet - but whatever - the idea is that we dont have a bunch of spaghetti taps running parallel cells together. The only OEM that does this is Zero Motorcycles and it will eventually go away )

Modules are broken down to 60Vish for safety reasons. This is a part of the manufacturing process and avoids a lot of hazard.

So.. in EV's... when you see module breakups... that is driven almost completely by the practicalities of the Manufacturing line.

-methods

I thought I did, sorry if I was unclear.

No need, and just want to focus on the foundation layer first, otherwise more convoluted than necessary.

Those Makita modules' "lowest cell level groups" are not paralleled together, and that is the question at hand.

Can the two "dimensions" of interconnectivity be active at the same time?

Will all the "A's" cross-balance each other as if a single 35P without any active assistance?

And will each "35P A group" usefully get monitored **as if a single cell** by my hypothetical "voltage only BMS"?

Ignoring any other BMS-like functionality for now.

Alright, I'll keep it simple, omitting protection/balancing circuits, just cells and wires.

While it is true that cells do automatically balance their parallel'd neighbors, if they are significantly out of balance, a huge dangerous current can flow between them. Which is why there are no battery systems on the market like that. Modular batteries are "isolated" on the cell level to make them safer.

Simply put, by connecting them at the cell level, you'd be shorting together 2 groups of cells with potentially very different charge levels. For example: 1 parallel group of cells could be fully charged, and the other parallel group could be at 10% charge. A huge current flows from the fully charged cells into the lower ones, and 2 minutes later, you hear a loud FSSSHHHHTTTT and we have a lithium fire.

 

[methods]

Agreed.

Back in the old days we used single pack terminology. Sometimes in an incorrect way.

There is most certainly a difference

If balance taps (or strips or whatever) are used... well... then it does not matter all that much
BUT
Some people literally take two 24S strings and wire them in parallel only at the power taps - and in that case - we most certainly want to now that

-methods

All of those packs have the same S/P:

3S 4P

You can call them 4P 3S if you want. Doesn't matter.

I know people usually put the S value first, but on other DC electrical forums (fora?) it is considered more accurate to put the "lowest level" first.

So 4P3S it is, to be nitpicky.

That is, as long as things are wired "normally", with groups connected in series via one big fat wire each, only.

With this possibility (which I don't yet understand) of both S and P happening at the same time? I guess it truly matters not. . .

 

[methods]

Nice knowledge dump.
This is my favorite: "Do not embed complex assumptions into your question that may or may not be true."

That is some damn good advice.

I have witnessed more arguing in my life because of the above than anything else. It is a form of Logical Fallacy similar to "The Complex Question". Also... the other fallacy which presumes something un-proven to be true -

"so, how long has it been since you stopped beating your wife"?

... The argument occurs due to something true being bound to something false... and... nearly all religious wars and arguments are fundamentally revolving around this fallacy... which I believe... is rooted in people <SNIP>

Every thread has something to teach everyone.
Those who lived before public forums remember... how valuable... it was to talk with folks who have experience.

-methods

I think for simplicity and thread hygiene better to just start a new thread for each question.

Lay out what you actually want to accomplish, as specifically as possible.

Ideally with diagrams.

Do not embed complex assumptions into your question that may or may not be true.

Lay off the jazz analogies, never mind about past errors or your feelings.

Don't bother editing past posts, just let such threads die and start anew phrasing your new topic questions better based on your growing understanding.

______
> What DIY pack size (not powerwall) and its application are best served with the use of parallel fusing?

DIY or not has nothing to do with it.

Size is not really relevant.

Do you mean paralleling multiple packs together? If not, then do you mean paralleling cells to form the 1S groups at the lowest level of a pack?

Again a drawing would help understand your use case.

Most packs only put fuses (if any) on the main power wire.

Internally I've seen fusible links as with Tesla packs, but those are used on a per-cell basis.

______
> Should DIY pack S/P negative cell end connections be sized differently than positive end connections?

In general, my answer is no.

I would phrase it: Why does this example testing rig have different sizing for positive vs negative?

 

[methods]

This is the sort of punk attitude that results in getting flamed.

Those who seek honest help from good people should avoid this behavior.

Somehow the poster is mixing up Engineering Correction coming from Experienced Members with his personal feelings or ... eh ... I dont know. ... But it is no good and it is the sort of ridiculous fighting that gets threads shut down.

Something is either TRUE or UNTRUE
A Test is worth a thousand opinions
It is always best to come back with a PROOF than to defend using prose.

-methods

Dearest John,

In case you hadn't noticed it wasn't you who started this S/P thread. Besides i already believe i know the answer to my two relatedf S/P questions and was curious to see how either you or amberwolf might reply.

Actually our reply is no surprise and to be expected as you've never wanted to answer one of my questions, but rather rebuke/demean me in one way or another. Like previously mentioned you as much to discredit yourself as discrediting me. Not by what you know or don't know, but rather by your bad notes.

Amberwolf you'd better digest john's post and not reply to either of my latest two S/P related questions as this S/P thread has apparently run it's course. So PLEASE don't further this thread by replying to any more of my stupid questions. Frankly, i doubt john will ever get it as he's so into himself.

With all the time john spends posting on ES threads with his frequent posts and his DIY expertise why is it he's not a moderator at ES

Yours truly,
Chalk

 

[methods]

Deleting this thread from my Email pings.

Sorry for the splash of responses, I dont have time to interact in "real time" as much as I used to. Maybe later.

-methods

 

[john61ct]

Yes at a certain point best to just cut your losses

 

[eMark]

my 14s4p have 4-14g positive wires and 4-14g negative wires coming off the pack/ 1 for each P so I pull current straight through pack. then it all gets soldered into 1 positive and 1 negative

Happy Trails in 2020 to you and your parallel "groups"