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Hi to all  Big Grin
My name is Velimir, I'm sysadmin and I love to play with electronics, but unfortunately don't have much time for that hobby  Sad

One year ago I have start to build small solar panel for testing (10cells 5V 47W), but then realize that voltage is to low to start digital voltage/current meter, so I bought 10 solar cells more. When I saw that solar panel is working I was thrilled  Big Grin , so I decide to try to make small 18650 battery pack to power TV. Now I'm working on that  Smile

Plan is to make 3S 12P battery pack from recycled laptop cells and enlarge solar panel to 27 solar cells, that is maximum that I can putt in existing custom made solar panel  Smile
Right now I have harvest 28 cells, so 8 more to go, and a lot of other things to do  Big Grin
Pictures are coming as soon as possible  Smile

I have found very useful information on this forum and on members youtube channels for making Powerwall, so thank you all for that contribution, it really help me to push this project from stand still  Smile
I hope that I will manage to build my own powerwall in combination with solar panels in short time  Smile

Keep in mind that the voltage range for a 3S lithium battery is about 9.0V to 12.6V and that might be a bit low for a 12V system.
(09-13-2017, 10:34 AM)DarkRaven Wrote: [ -> ]Welcome!

Keep in mind that the voltage range for a 3S lithium battery is about 9.0V to 12.6V and that might be a bit low for a 12V system.

Hi Dark :-)
Thanks for the advice, I appreciate that :-)
I was thinking to use 4s or 3s but I decide to try first with 3s and see how will go, and later I can add 12 more cells and make 4s
4s is between 16,8V and 12V, and 12V inverter work from 15,5V maybe 16V to 9,5V when it shuts off. And if I use 4s then voltage will drop to 2.35V and I don't want to damage my battery's   Big Grin 
I can put some protection between battery and inverter so it won't let voltage to drop below 3V but then I will complicated the system.
And if i use 3s voltage will drop to 3,17V, so its close to perfect, in theory  Big Grin
I don't intend to charge them more then 12,3V

Again, thanks for advice, I will keep that in mind and if system doesn't work it will be upgraded to 4s  Smile
Fello sysadmin here as well, nice to meet you Wink
Glad to be of service, but 4S probably isn't a solution either because, as you've said, fully charged the voltage is a bit high. With lithium cells only 7S is suitable, for a 24V system that is, but then you need a different inverter.
If you have the 12V inverter already you could either do 3S with a buck/boost converter (stable 12V output from 9.0V to 12.6V input) or 4S with a buck converter (stable 11V output from 12.0 to 16.8V input).

12V inverters usually work between ~10V and ~15V. 3S will work for a start but you won't be able to use the full capacity of the cells. 10V loaded for 3S could mean, depending on your load, 3.5V or more resting voltage per cell. We're talking about 50% capacity you might not be able to use for 3S. With 4S you can't charge the cells to more than 3,87V, otherwise the battery will be above 15,5V. Same principle, thel cells will like this as it means an easy life for them, but you can't use their full capacity either.

But surely, you can test this yourself and see what the result is. Maybe it fits your needs. The cells won't mind 50% DoD, they will like this.
You could do 4s with just a couple of diodes in front to drop the voltage rather crude.. Note that running 3s.. On a startup or spike the voltage will quickly drop and the inverter shuts of rather early Smile
(09-13-2017, 01:25 PM)zag2me Wrote: [ -> ]Fello sysadmin here as well, nice to meet you Wink

Hehehe  Smile , nice to meet you to Zag Smile
I think that here every member, or every second member is involved with IT stuff  Big Grin

Darkraven and Daromer thanks for advice  Smile 
Right now I'm little short with cells, when I collect some more, project will continue  Smile and then maybe I will open new topic  Smile

It's rely nice to be here and talk with people that have knowledge in this stuff  Big Grin