Beginners Guide to Processing 18650 Cells | Cell Database


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Canuck RV Battery
#1
Hi All,

I am currently working on a replacement for 2 Flooded lead Acid batteries I have out at camp with 18650's

What I've got

 - Cheap 20A PWM charger controller but has been good for the lead acids last year.   
 - around 100 x 18650's so far about 1/3 above 2000mah the rest between 1500-2000
 - 3d printed cell holders from a nice customizable CAD file from thiniverse.com
 - Going to start with a Bank of about 20Ah @ 7s to be charged from 4 panels (2 40W and 2 60W in 2s2p) 
 - Fusing both sides of each cell and I am going to run a BMS just not sure which one as of yet.  Or arduino Based
 - 24V to 12V buck converter to run my camper as I only use 12V out there and I have zero need for AC.
 - Charging the cells for testing with a bank of 8 TP4056's and Discharging with a Hyperion RC battery charger/Discharger  - this allows me to Discharge @ 10A for my 20Ah packs in a more real world application

I hope to keep this as cheap as I can but still having a safe Pack build

I'll post picks as I go but just playing with the little time I have (3 kids lol)
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#2
Sounds pretty good and you thought things out pretty decently. I was starting to wonder what voltage you needed, then I got to point 6 Tongue

Not sure of efficiency purposes, but could you use a 1:1 transformer with a center tap on the 2nd coil to get your 12volts? You'd have two hot's and a common negative. I havn't really asked this question in any other forum. But would it work? Would it have better/worse efficiency over a buck converter?


Are you going to use a casing similar to the LA design, or are you going for a completely different layout? Just wondering because of where you may be putting the Li-Packs. Are they going into the same storage area as where the LA's where at?

You probably wouldn't need to do the extra work of fusing "both" sides. I know some on here have done that, but many more only fuse the one side. I personally would fuse the Positive end as if it's blows, there's no more contact anywhere. As noted by AverageJoe and others, when a cell starts to short, it's not 'that' cell that's going to blow the fuse. It's going to be all the 'other' cells dumping into that one cell. That's what blows the fuse. So, my theory imho, is if you have 2 fuses, more power can be dumped into the dieing cell before it's cut off from the rest. As the current is being shared between two wires, effectively. One wire I would assume would blow faster than the two.

I like the idea of being able to discharge at a real world of 10A controlled to really see how the pack responds. I'll have to remember to do that when I set mine up.

Waiting for those pics Smile
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
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#3
Hey Thanks,   Yea I want a 24V so the PWM charger will charge and discharge within a acceptable tolerance to not over charge and over discharge.  I watched all of Adam Welches (sp?) videos on this and it looks promising

Here are some picks of my setup.   I have a small number of cells right now but still takes a bunch of time to go through them.    

The cells I have in packs now are in the 11-12 Ah range Tested on my Discharger with the home made white battery holder on the right is in parallel the one on the left is for individual testing.   Again coroplas and got glue with house wire for the connections.   Real Cheap!

I'm not looking to maintain a certain size just experimenting on using these cells for energy storage.   Once I get more cells I will be making more cells in the same Ah size.  My thoughts are to slowly grow the capacity and be able to play with packs without too much mass of cells.   Eventually once tested and proven I'd look at combining banks together.   

I have been double testing the batteries as I have found even back to back capacity tests have shown up to 100mah of difference so I have been averaging the numbers.    

I'm waiting on some fuse wire and going to be doing my own testing like averageJoe did as my bank is going to be Away from my camper but still would like to avoid a fire.  

Cheers
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#4
LOL love your cell holders on your charger!! Brilliant! Wink

Nice setup and load out. Looking forward to more
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
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#5
Thanks. The chargers I have from racing RC cars and the Charging board is just a low cost way to hold batteries to charge with the tp4056's
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#6
Good stuff, is that a PC power supply you've repurposed?
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#7
Yea I had it setup to power my rc chargers on the 12V rail but I have s more powerfull one for them now so I changed to the 5V rail. that PS will do 40A at 5V which is nice. Once i get some of the dischargers they will go beside the tp4056 on the board.
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#8
I got 4 Packs wired All except the fuses (5A) but for testing I have some thin guage stranded wire as standins.   3 of the packs Discharge to 23 Ah (+ -) 100mAh 

 Last one still charging before I run the discharge test on it.  My goal is to have each pack within 500mAh of each other so I'm off to a good start.   

As I get more cells I will be adding banks in 7p increments in the same Capacity range


So comparing to my Lead Acid batteries I should be within 5% of the effective capacity once I get by buck converter installed with this pack  (23Ah @ 24v) taking the voltage down to 12V @ ~40Ah
Korishan likes this post
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#9
Alright I have all 7 packs assembled and tested at 22-23Ah packs

I am just waiting on my fuse wire which should be here next week.   Uuug waiting for stuff from china is brutal in canada!!

I am now thinking about mounting my packs and have come up with 2 designs in sketchup to hole my cells.   one is a side holder one is a back holder which grabs both cell holders.  Here are some pic

Here is how I think it will work
Andreas Kvernes, Korishan, BlueSwordM like this post
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#10
That looks like a fantastic design!
http://www.hbpowerwall.com for a full video diary of my project.... 
https://www.amazon.com/shop/hbpowerwall to buy stuff I use Smile 
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