What about an 8s 4p 24V configuration?

Svalbard

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What about an 8s 4p 24V configuration?

First I was planning a 16s 48V system in my boat and was thinking 2 x 16s in parallel. Now I have changed my mind and want to go for a 24V system. Then I read that it is not good practice to connect more than two lifepo4 batteries in parallel.

What if I buy 32 brand new cells from same production batch hopefully with same internally resistance?

The reason for 24V vs 48V is the alternator. I cannot get a 48V alternator for my engine. Balmar has a powerful 24V alternator that fits my engine. Together with an external regulator.

In any case I assume I need one separately BMS for each 24V battery. I am thinking of DALY 250A w fan. BT and UART. Would prefer no fan, but want to be able to charge fast. Both with the alternator and generator via a Victron Quatro 24/5000 or 8000.
 
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Steve_S

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You can connect as many packs in PARALLEL as you want, Series is NOT a Good Idea and do not exceed 2 packs in Series.
Packs in Parallel increase Amp Hours. Packs in Series increase Voltage.

Bulk/ Commodity cells are NEVER Matched & Batched, at best they are Voltage & IR Matched at the storage Voltage the vendor gets them at. These are mostly end runs, grade-B or at best Grade A- or worse. These are really unsuitable for use cells in Parallel within a Pack.

Fully Matched proper Grade-A Cells come with a Testing Report that shows the IR (Internal Resistance) at different measurement points. PS, It's not some dork sitting there with a handheld metre reading IR, it is a long test process. VERY FEW Vendors carry those as they are more cost (the testing takes a LOT of time & Labour), ONLY Matched & Batched cells are suitable for making battery packs with cells in parallel within.

CHARGING VIA ALTERNATOR is a Royal PAIN and possibly very Dangerous ! The RV & Marine Folks have had to tackle that monster. I am NOT a Mobile person so I cannot address that BUT it IS addressed here in these Docs by Marine Folk who know the score.

This is 4 Packs in Parallel:
1633597633449.png

Cells Assembly for 24V, bottom showing cells in Parallel within a Pack.
1633597787847.jpeg

Hope it helps, Good Luck.
BTW: I know of only ONE Vendor selling Factory Matched & Batched Grade-A cells, and that is Luyuan Tech (Amy Wan) who is a very well Known Good Vendor here... https://szluyuan.en.alibaba.com/productlist.html?spm=a2700.shop_index.88.17.6d601a4dmT6rif
 

Svalbard

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Thanks. I am in contact with Amy. She promise me brand new grade a cells. All from the same production batch. And with test reports.

Charging with alternator is no problem as long as you use a Balmar or a WS 500 regulator.

So what you are saying is the best is to parallel 4 and 4 cells first. Then put those in series?

And only 1 BMS?
I am thinking of 123 smart bms because they can talk with Victron Quatro and probably also the WS 500.
 

Svalbard

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The reason why I ask is that some are saying maximum 2 Lithium packs in parallel. I was planning 8 cells in series to get 24V. Times 4 in parallel to get Ah/ kWh. And one BMS for each pack.

Alternatively I could put 4 and 4 cells in parallel (groups of 3.2V), and series those together in a large 24V battery with only one BMS.

Will there be a problem with the latter since 4 cells are in a group on each BMS cable? The individual cells are then not maintained?
 

Steve_S

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Paralleling Cells inside a Pack is not the same as Paralleling Battery Packs.
Paralleling Cells is NOT a Good Idea with such large capacity cells and most especially if they are NOT Matched & Batched properly.
A Standard 24V/8S configuration with a BMS & Fuse per Pack is the BEST way to go.
8S BMS with 8 Cells = Each cell is watched / monitored and optimal pack health can be maintained.
Paralleling Cells "Ghosts" them, so if 2, 3 or 4 cells are in Parallel they appear as "one" to the BMS.

Packs in Parallel Divide Load & Charge proportionately to the Pack Size.
IF Properly configured, each pack can act as a "Last Man Standing" should the other packs cut off for any reason.
 

Svalbard

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Thanks. That was my plan until I saw Wills YouTube telling more than two lifepo4 packs in parallel is not good? And also other places.

However I will get 32 top brand new grade a from Amy so probably no problem.
 

Steve_S

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Thanks. That was my plan until I saw Wills YouTube telling more than two lifepo4 packs in parallel is not good? And also other places.

However I will get 32 top brand new grade a from Amy so probably no problem.
Please LINK that Vid.
Many people fall over the Series & Parallel and the context the terms are used in.
I run 5 Packs in Parallel we have one member here I know of with 10 48V Packs in Parallel.

Packs in Serious should be obvious.... Imagine have 4x 12V packs to make 48V in Series and one fails. If charging that is instant Overvolt, if discharging that is a full on fail cutoff. Now picture what a 12V BMS will do when 48V hits it.

The Victron and other manuals I refer people to all talk about using batteries in Parallel and proper configs... A few of us have been at this for quite some time.
 

jasonhc73

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I have 4, 48V LiFePO4 batteries in parallel. Working fine for 2 years now.

I don't see any limit at all other than your wallet and space to how many batteries you can parallel any battery, regardless of voltage.
 

Svalbard

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Yes, Victron even has lifepo4 batteries that should not be paralleled?

And now I received an answer from 123 BMS in the Netherlands asking me why I don't parallel 4 and 4 cells and make one large 24 battery. Making me confused...

I just placed an order at Amy. US$ 4000 for 32 EVE 280Ah K Grade A. I arranged shipping myself from my local shipping agent. They will arrange a pickup from their warehouse on Sunday. Then they promise 1 week before I have them here close to the north Pole. Let's see...

I will see if I find the link to the video.
 

jasonhc73

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Yes, Victron even has lifepo4 batteries that should not be paralleled?

And now I received an answer from 123 BMS in the Netherlands asking me why I don't parallel 4 and 4 cells and make one large 24 battery. Making me confused...

I just placed an order at Amy. US$ 4000 for 32 EVE 280Ah K Grade A. I arranged shipping myself from my local shipping agent. They will arrange a pickup from their warehouse on Sunday. Then they promise 1 week before I have them here close to the north Pole. Let's see...

I will see if I find the link to the video.
You confusion is about to get worse.

Anytime you connect any "battery" to another "battery", you just created one new battery.

A typical 12V car battery is 6 2v cells.

You only see the two battery posts on the outside of the big plastic cover.
On the inside of that big plastic cover is 6 smaller 2V batteries wired in series,


Read the Wireing Unlimited book. It's great.
 

Svalbard

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As far as I hear he is saying it is best to parallel the cells first. Then put them in series.... I don't believe. Then the BMS monitoring and maintenance will not be per cell individually.


Screenshot_20211007-195228_Chrome.jpg
 
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Svalbard

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Yes jasonhc73. I know. My question of this topic is very simple. I have ordered the cells. Should I then order 1 8s BMS or 4 8s BMS. After reading your answers I go for 4. Then I create 4 totally separate 24V "batteries" out of 8 cells and one BMS.

Then I parallel them regardless what many says.Screenshot_20211007-185809_Chrome.jpg
 

jasonhc73

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Yes jasonhc73. I know. My question of this topic is very simple. I have ordered the cells. Should I then order 1 8s BMS or 4 8s BMS. After reading your answers I go for 4. Then I create 4 totally separate 24V "batteries" out of 8 cells and one BMS.

Then I parallel them regardless what many says.View attachment 67892
You are making the battery. Do you want to know what 32 cells are doing or 8 cells are doing?

It is your $ you are spending.

If new grade A cells, I'd go 4P8S, resulting in one "battery pack".
If used old cells, I'd go 8S times 4.

New cells made practically at the same time will have very close internal resistance and be essentially identical.

I've used 5 different "BMS's" and have settled on this conclusion;
"Never buy used batteries, again."
"Don't buy a BMS, buy an active cell balancer. Only use the cell balancer during float time."
"Only balance the cells when they are more than 0.35mv out of balance."
"Use a Victron Smart Shunt".
"Use the SCC and Inverter for the top and bottom cut offs"
 

Ampster

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What about an 8s 4p 24V configuration?
I am one of the few on this forum that doesn't have an issue with multiple cells in parallel. However the use case can determine the optimum configuration and many boaters value the redundancy that two packs might offer.
 

Svalbard

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Yes, I will go for 4P8S. Because the cells are new Grade A matched, AND because I have read the manual for 123SmartBMS which is the one I will use for my system. It communicate with Victron Quatro and can be configured also to communicate with the WS500 regulator for the alternator.

Cells are ordered and also alternator. Decisions made :)
 

Mcgivor

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My first build was a 4P 8S pack with 100Ah cells , it's been in service for 3 years without any problems, the cell blocks remain in ballance even when fully charged, which is not done on a regular basis, normally a lower value is used, ~90%, initially top ballanced.

Whilst I understand the logic behind the theroy of not parrallel connecting cells to add capacity, thus losing individual cell protection, the information used during my build suggested that parrallel first was the preferred method, additionally the use of lower capacity cells was recommended due to their physical robustness.

As with anything there are advantages and disadvantages of any topography, along with varying levels of redundancy, individual opinions likewise vary, personally I wouldn't suggest one method over another other than to share my experience.
 
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