Fortune 300A System

[Wapst]

Hi ,

Read will's book, but wanted to clarify a question about building my own battery for a CamperVan

I want to build a 300-400A Battery with fortune cells. Can i do this with 12 to 16 fortune 100 Cells - wired to a single BMS
or is the 1 BMS per 100AH the better strategy?

I see the 4s BMS strategy that is recommended --- but some of the newer videos had me curious.

I saw this BMS on the site linked by Will - https://www.electriccarpartscompany.com/BMS-48V-Lithium-Battery-Packs-Choice

is that a better choice for a 300-400AH battery or just flashier with the LCD readouts?

Thanks in advance

 

[tictag]

Can i do this with 12 to 16 fortune 100 Cells - wired to a single BMS
or is the 1 BMS per 100AH the better strategy?

You can buy BMS's up to around 32S, should be no problem getting a 16S BMS.

is that a better choice for a 300-400AH battery or just flashier with the LCD readouts?

Definitely has 'go faster' stripes on it! There are many BMS's on the market (just search this forum). This is just one of many.

In general it's best to have a BMS per 'battery', defined as a collection of cells. If your battery is 16S, then get a 16S BMS. If you are connecting two 8S batteries in parallel to make a higher current battery bank, get two 8S BMS'.

 

[HRTKD]

Technically, you could get to 400 Ah with a 4s BMS. The battery arrangement would be 4p4s and would give you 400 Ah at 12v.

Each lead from the BMS would connect to one of the batteries in each of the 4p collections.

Unless you had perfectly balanced cells that stayed balanced, I would be reluctant to run a 4p4s arrangement. It's just a lot of battery cells without enough granularity of observation. One cell in a 4p collection could be bad or less than optimal and the other three cells may carry the load and you don't know about it.

 

[Wapst]

Technically, you could get to 400 Ah with a 4s BMS. The battery arrangement would be 4p4s and would give you 400 Ah at 12v.

Each lead from the BMS would connect to one of the batteries in each of the 4p collections.

Unless you had perfectly balanced cells that stayed balanced, I would be reluctant to run a 4p4s arrangement. It's just a lot of battery cells without enough granularity of observation. One cell in a 4p collection could be bad or less than optimal and the other three cells may carry the load and you don't know about it.

Thank you! Is there a "rule of thumb" with how much granularity in the cells is usually good, so 2p4s x 2 for 400ah good? or would you go even deeper down to the cell level? 4s x 4?

Assuming a battery such as this: https://www.electriccarpartscompany.com/Fortune-100Ah-Aluminum-Encased-Battery

 

[tictag]

Personally, my rule of thumb is one balance lead, one cell. Other opinions are available!

 

[HRTKD]

Wapst, if you have the room to create multiple 4s batteries and then parallel them into a common busbar, that's probably the better way to go. It certainly has the finest granularity of cell observation and balancing. I'm planning to do 2p4s for reasons of space. It can certainly be argued that 2(4s) and 2p4s takes the same amount of space for the cells. But I have to also take into account an extra set of cables, cable lengths, perhaps a larger busbar and space for a second BMS. That said, the folks that have more experience may convince me to not go the 2p4s route.

 

[Steve_S]

TESTING, there is an error in posting responses. disregard is this is seen.

 

[upnorthandpersonal]

The below text is by @Steve_S - there were some issues posting a reply...

TBH, I am one who recommends no paralleling of these LFP Cells. Mostly because when you Parallel cells you are effectively ghosting them and there is no fine monitoring or management as a result. Partly this is an issue because these LFP Prismatic Cells have a LOT of AHr storage compared to say the small 18650 Li-Ion cells, the bigger the cell the more it can vary during the operational cycle. The larger the cell capacity the more potential for variance between the cells.

Example:
Take 4 cells in parallel, Cell 1=2.50V, Cell 2=3.00V, Cell 3=3.20V, Cell 4=4.0V The aggregate average which is what the BMS would see for this "set" is 3.175V BUT in this example, you have Cell-1 @ 0% SOC and Cell-4 in Overcharge @ 4.0V and you'd have no way of knowing and the BMS could not balance / correct for this (provided the BMS has balancing capabilities). A good BMS will monitor each cell and if one or more goes out of spec during charge/discharge it should disconnect the pack to prevent damage to the cells and protect the pack as a whole. A BMS cannot do that if it cannot see the status of each cell and therefore the potential of harm to the pack remains (and that can affect your wallet too).

NB: This is common with Pre-Built battery packs available from some vendors who are using dubious cells to begin with such as ShunBin, where they install used cells and ghost bad ones with good ones to build packs that they flog. Not only myself but others have fallen prey to that tactic and was a "very expensive" lesson that others should avoid.

The LFP Game "sorta" because of the large capacity the cells can have the importance of balancing and keeping them balanced is key to ensure that everything continues to work for the long term. When buying Premium Cells which are Voltage & Resistance Matched "properly" you will pay a premium (about double) as it is a time-consuming exercise, as well as a costly one as cells, are sorted & categorized into sets and the elimination of those "out of spec" get binned. The majority of the vendors will Voltage Match as that is simple and cheap but not Resistance Match cells. The result is the cells can "wander" more within their specs and therefore need some more attention in regards to managing - balancing.

Hope that Helps, Good Luck.

 

[Wapst]

in this video from will -- he has a battery monitor with the BMS

using a Daly BMS such as - https://www.aliexpress.com/item/32921412658.html?spm=a2g0o.cart.0.0.4ce73c0074l5Mn&mp=1

do you get the ability to see the health of the cells on UI or do you need a separate device?

Thanks!

 

[tictag]

AFAIK, the 'typical' Daly BMS's (the one used in Will's video) do not have any method of controlling parameters or reading data - you have to buy the right one for your application. They do, however, offer a range of Smart BMS's, which do.