12 V 200 AH LiFePO4 battery construction? - Page 1
Forum section: electronics / projects

author: Renate
author_rank: Super Contributor
timestamp: January 22, 2021, 01:52:03 pm
content: I've been in the market for a 12 V 200 AH LiFePO4 battery.It seems that everybody and their uncle in China makes them.There are lots of them in the BCI 4D/6D/8D size range. (520 mm x 260 mm x 260 mm, 20.5" x 10.5" x 10.5")I saw one of them disassembled, it was just a trunkful of 18650 (or whatever) cylindrical cells all spot welded together.Are they all like this?I see another style, that is the same capacity but almost half the volume.This comes in "brick" cells that you jumper together.https://www.amazon.com/LiFePO4-Lithium-Phosphate-Off-Grid-Applications/dp/B07PW4R4PSDo the bricks make sense? They are certainly more compact.

author: strawberry
author_rank: Super Contributor
timestamp: January 22, 2021, 04:05:40 pm
content: prismatic cell is low weight less volume and easy to assemblebut less surface area for cooling and case is not as durable as cylindrical cell

author: Renate
author_rank: Super Contributor
timestamp: January 22, 2021, 05:33:55 pm
content: Quote from: strawberry on January 22, 2021, 04:05:40 pmThere seem to be two types of cases for prismatic cells, plastic and aluminum.I learned another good word besides "prismatic" and that is "graphene".All the literature speaks of it highly but it doesn't seem to have permeated the market yet.This offer on ebay looks pretty good, 4 x 3.2 V 272 AH graphene LiFePO4 for $729 US:https://www.ebay.com/itm/4-New-3-2V-272Ah-Graphene-10K-cycle-Lithium-Iron-P-LiFePO4-size-like-280ah/233865918660They speak of 10,000 charge cycles.Still, even 3000 daily cycles is over 8 years.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 22, 2021, 06:27:08 pm
content: There are dozens and dozens of sweat shops manufacturing those plastic-case, prismatic LFP bricks in China, they claim to heavily compete against each other (and generate some drama; see Winston Chung / Thundersky) yet have complete price fixing year after year. No "real" manufacturer does those, at all.They suffer from really low energy density like 90 Wh/kg, this is of course OK for stationary storage.They can give any ratings they want, they show you the specs you want to see, it's not based on actual measurements and there is little quality control.Common strategy is to add random cool techy words and claim their batteries contain that. Winston was claiming they use "Yttrium" for magical properties, apparently someone else got graphene now!

author: strawberry
author_rank: Super Contributor
timestamp: January 22, 2021, 06:45:15 pm
content: https://en.wikipedia.org/wiki/Lithium-titanate_batterycan reach 20k cycles but less energy compared to LiFePO4safty comparisonhttps://www.researchgate.net/figure/Overview-of-main-degradation-mechanisms-in-Li-ion-cells-9_fig5_334842395

author: Renate
author_rank: Super Contributor
timestamp: January 22, 2021, 11:52:11 pm
content: Well, that video taught me a lesson!I'll never put a fire axe through a battery.It seems that this "graphene" in the title of the product offer is not substantantiated in any other way on that web page.Still, looking at other DIY websites it seems that the Lishen 272 AH cells @ $80 US from China is very popular.

author: Renate
author_rank: Super Contributor
timestamp: January 23, 2021, 07:42:15 pm
content: So, just a few other data points FWIW:I used to have a single BCI Group 27 lead/acid battery.That fit in a tray for the battery that is 6-13/16" wide.I decided to replace that 80 AH battery with two 6 V 224 AH GC2 ("golf cart") batteries.So, after a bit of cutting, grinding, bending, welding I had a 7-1/2" wide tray long enough for the two batteries.Now, I'm planning on going over to lithium.The Lishen 272 AH and the EVE 280 AH have a width of 173 mm.That is, 6-13/16"

author: mzzj
author_rank: Super Contributor
timestamp: January 24, 2021, 08:03:05 pm
content: Quote from: Siwastaja on January 22, 2021, 06:27:08 pmLifepo4 energy density is not that bad if you dont need high current capable cells.~280Ah cells that are currently flooding the market are about 140Wh/kg.These are also really attractively priced at about 100usd per cell.(All of these cheapos are possibly B-grade of some sort but more than few sellers have units that have the claimed capacity.)Diysolarforum.com seems like most active forum on these. Probably best to check recommendations and warnings over there for aliexpress/alibaba suppliers.