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Questions about 100AH build.
#1
Hi all, this is my 1st post on the forum after reading lot of threads i decided to start with the basics cause sounds little complicated. I would be really grateful if you can help.

I have a small solar system. After many years of using AGM or LeadAcidBatteries to charge from my solar panels (3 x 50w connected in parallel) i decided to move on to 18650 lithium batteries and build a small power wall.
My needs are very basic , main plan is to use my 85w laptop all the day with the sun + charge the battery and in the night without problems for 5-6 hrs together with 3 x 4w 12V led lights. For the laptop i have a 300W 220V inverter that is more than enough for what i need and sometimes i might use other small devices like the 40W soldering iron. For mobile etc i charge them via the 5V usb ports of the charge controller or with adapter from 12V car cigarette lighter to USB. 


I plan to use recycled 18650 batteries as already i have plenty of them from old laptops to start from. If i understand correctly the mah to AH conversion i make an hypothetical calculations: let's say that i have 50 x 18650 batteries 2.200mah this would give me a 100AH battery? I understand because of the old cells i would not get that exact number but based on this example is my math correctly and it can be simple as that?

Hopefully you can help me to build my system and get rid of the heavy batteries that i need very often to change (35kg for 100AH lead acid that i must soon change) and is so difficult to carry on hand, i do this for hobby but also is important for living as i do not have electricity in my hut!
So next time i move to the city what should i buy including wires, fuses, bms etc?
Safety is VERY important for this project as i live in the forest so apart that of course i will everyday monitor the system i will have to be secure that will not start fire if i'm not there for 1 day.

I am attaching a picture of my 1st attempt to create a very small battery with 6x 2.200ah cells all of them charging good to 4.2V , can i connect this battery +/- to the solar charge controller (PWM chinese with LCD) and use it as a test on my 12V lights or it my approach is completely wrong?

My soldering skill is not excellent as you will see but i can manage with patience, i used sandpaper and flux before solder the cells, i want to know if my connections are wrong and other suggestions for further expansion of the battery.
Right now i have 24 x 18650 2.2200ah good cells , this would give me about 50AH battery? How should be connected in series or parallel? is 4s 6p correct? (this means 4 series of 6 batteries in parallel?)

thank you so much!
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#2
Your six batteries together are parallel ? then you have still 4 Volts, not 12.
Your red drawing in the right side seems to be nil, you define the connection between cells as plus and minus simultaneously.

Be so kind and look here
https://secondlifestorage.com/t-What-is-...difference
https://secondlifestorage.com/t-What-doe...ric-digits

for some startes.
1 kWp in Test
4 kWh battery target - plus Mobile Home battery
Ultra low cost
Electronics ? No clue. Am machinery engineer.
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#3
Cherry67 thank you very much for your fast reply , at this point any information for me is gold and those threads are very informative, simple and clear.
Can you tell me in my 1st post picture if the problem is the position  (sXp) of the cells or that i did soldering all together?
I guess to solder each cell together is not the correct method? This was an idea for parallel connection but from what i understand i should do parallel together with series? First goal is to make a test with my 24 x 18650 cells.
I made a new diagram for 6 cells again , can you check it and tell me if the soldering is correct or my math for V is wrong?
Thanks!

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#4
Both drawings in the last image are not parallel. They are serial.  Parallel is all Pos ends are connected together, and all Neg ends are connected together. Then  you have 1 large battery with still the same voltage.

And, even assuming the drawing was meant to be in series, the suggested voltage is wrong, at least the right one
6 * 3.7 (nominal) = 22.2V, or a low value 24V system. 7s is usually used for 24V.

Maybe instead of drawing 2D flat top images, perhaps do a 2D side view of your ideas, where you can show which Pos and which Neg are paired together to mean 1 cell. In the above images, we can't really tell if you have 6 cells, or 3 cells.


Here's kinda what I mean....

Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
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#5
Korishan thank you for your reply.
You are right about my diagram it meant to be both in series and you are right also about the calculation i just did a quick math of 3.5V x 6 = 21 so your math is correct about the voltage increase in series.
So to come closer to my goal, let's say that i have 24 good and identical cells to start my experiment : should i connect in parallel or series?
And about safety , i should solder this BMS controller and then from the cells +/- can i connect it through my solar charge controller?
How can i make 12V from 24 x 18650 batteries and so on .. ?
I am not sure about the 12V system but always my AGM or lead acid batteries were 12V, i use lot of 12V devices (LEd lights, laptop charge converter ..) and sometimes i attach to the battery 12V to 220V inverter if i need to use normal AC let's say to charge another laptop that i do not have adapter. I was thinking to stay the same at 12V.

What do you think?
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#6
12 Volt is something to consider:
https://secondlifestorage.com/t-What-lit...V-3s-or-4s

So its either 3 or 4 cells in series.

And there you can parallel a 2nd, 3rd ..... 3(4) s group.

then look again at
https://secondlifestorage.com/t-What-doe...ric-digits

There you see a 4s = 12 Volt 3 parallel group.
Korishan likes this post
1 kWp in Test
4 kWh battery target - plus Mobile Home battery
Ultra low cost
Electronics ? No clue. Am machinery engineer.
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#7
24 2.2 AH cells in a 4s6p would give you a 13.2AH battery. 16.8 v to 12v. You would need 184 2200 mah cells in a 4s46p setup to get your 100AH.
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#8
ONLY if his devices can handle 16.8V. Even a lot of automotive grade devices can't handle over 15.5V. So that would effectively reduce the Ah capacity available with a 4s setup.

It would be far better go with a 7s setup, then use buck converters where needed, and a 24V inverter where AC is required.
bogptrsn likes this post
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
(this chat is not directly affiliated with SecondLifeStorage; VALID email req'd)
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#9
Okay I learned something, "buck converter". Thanks for that.
My first battery will be emergency generator 2 7s25p in parallel. Was wondering how I could tap 12v from it (for jumping the tractor off, ...). Have 400 18650 and looks like 10 more days to capacity check with 3 C4 chargers.

Back to regular programming, don't want to hijack this thread, but wanted to show how a simple post like this thread helps a lot of people.
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#10
Buck converter won't work for jumping a tractor off. Waaay to many amps. You would need something a lot more beefy for that purpose.
Now, you could use a buck converter with 16V super caps. Use the buck converter to charge up the caps, then use the caps to jump the tractor.
oloyeadeniran and BlueSwordM like this post
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
(this chat is not directly affiliated with SecondLifeStorage; VALID email req'd)
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