Questions about 100AH build.

alex_1978

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Dec 21, 2018
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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 andin the night without problems for 5-6 hrs together with3 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 coursei 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!

image_xkvbih.jpg
 
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 postpicture if the problem is the position (sXp)of the cells or that i didsoldering 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!


image_wimsrr.jpg
 
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....


image_pykmuv.jpg
 
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 identicalcells to start my experiment : should i connect in parallel or series?
And about safety , i should solder this BMS controllerand 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?
 
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.
 
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.
 
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.
 
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.
 
Can someone please confirm that my diagram is correct to start building the pack?
This will be my 1st 4s7p pack and then i plan to create more packs like this in parallel to keep the same voltage.

Thanks!

image_idfrfl.jpg
 
Considering it's been over 24hrs, I figured someone else would reply.

I think it looks right. It took me a little bit to work out the way you were wiring things because of the angle you have your packs. Maybe if you had them in isometric view instead of orthographic it would of been easier to identify. But that's just me.
Also different color wires for each one would of been good ;)

But, I think that's right.
 
Thank you very much for your reply.
Can i put fuse wires on this pack connecting the cells for more safety?Cause i've seen lot of people doing this on YT but they use parallel packs, i wonder how to do in series.

About the BMS wiring, does it have to be a sequence or should i be aware of something else?Or is it ok like i plan to do:B1,B2 on the bottom on the middle that there are 2 series and B3 on the top on the last series on the center.
 
alex_1978 said:
Can someone please confirm that my diagram is correct to start building the pack?

no, you seem to have b2 and b3 mixed up.

and polarity to the charge controller is reversed.


Hope That Helps.
 
DCkiwi said:
alex_1978 said:
Can someone please confirm that my diagram is correct to start building the pack?

no, you seem to have b2 and b3 mixed up.

and polarity to the charge controller is reversed.


Hope That Helps.

yes, correct. Thnx DCkiwi. They are reversed.

alex_1978 said:
Can i put fuse wires on this pack connecting the cells for more safety?Cause i've seen lot of people doing this on YT but they use parallel packs, i wonder how to do in series.

About the BMS wiring, does it have to be a sequence or should i be aware of something else?Or is it ok like i plan to do:B1,B2 on the bottom on the middle that there are 2 series and B3 on the top on the last series on the center.

I wouldn't put fuses between series connections. There's no need to put fuses between each pack, it serves no purpose at all. Especially since 1 fuse at the end of the string between string|charger and string|inverter is all that is needed.
You "must" connect them in the proper order, B-, B1, B2, B3, otherwise you will get to high of a voltage on the bms and possible blow it up. Like DCkiwi mentioned, B2 and B3 is backwards. Best case is the bms just won't turn on. Worst case is it blows up releasing the magic smoke.
 
DCkiwi you are right polarity on the charge controller! was just a mistake on the diagram and for sure i wouldn't do when connecting.
Can you please explain about the BMS wiring what is wrong?
Thanks!
 
get friendly with your voltmeter.

seriously!
 
DCkiwi said:
get friendly with your voltmeter.

seriously!

Voltometer and i are very good friends but before i blow the bms please advice :)
Can you explain me please what is wrong in the bms wiring?
are B- and B+ correct or should i connect somewhere else, cause this looks more normal to me.
B2 and B3 are mixed up, but B1 is correct?
So B2 should be B3 and everything else is ok?
Thanks!


this is what you guysmean?


image_wcglyi.jpg
 
alex_1978 said:
Can you explain me please what is wrong in the bms wiring?

sure ...

alex_1978 said:
B2 and B3 are mixed up, but B1 is correct
So B2 should be B3 and everything else is ok

thats it ...

alex_1978 said:

my pleasure. please call again! ;P


b1 and b3 MAY be reversed -- impossible to tell from your diagram. use voltmeter to check when making balance lead (to connect with BMS).

polarity to charge controller reversed (still).
 
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