Lithium-Ion power pack prototype

[laban93]

Hi!
I'm trying to make a battery pack for a 5v screen with a peak current og 8A and a average powerconsumption of about 2-300mA. The system is also going to be powered from a 150W solar panel with 22V out max @ 8A.
My plan was to use 8 18650 cells. 2 in parallel and 4 in series. the cells are unprotected.

Does anyone have some good reccomendations to get started at this? I know they have to be over and under current and voltage protected. I guess also that they have to be balance charged.
Do you know of any boards to use in this application? The form-factor has to be as small as possible, as the battery back is going to be mounted in a square tube, and the powersupply can be either inside the tube, or flat behind the screen. Is there a CE compliant multipurpose, Charging, MPPT regulator, buck conterter unit for this?
Sorry for my rusty english spelling!
-Simon

[soubitos]

Charging current per specs is Standard charge: 1075mA Rapid charge : 2150mA. a 4S2P pack would require twice as much so in real life terms 2-4Amps MAX.

You can find plenty of CC-CV modules around in step-down step-up or step-up/down configurations which you could use with the solar cell mentioned but it is quite a big one and perhaps you need to use a smaller one instead... or make a 4S4P pack instead or even larger... (I recommend a module based on LTC3780 step-up/down 10a max for under 10$)
Then you need a suitable BMS which again, there are plenty around....

[ocset]

I  would just shove a voltage sense on each cell.....soon as any cell goes overvoltage...stop charging  them.
When you stop charging them, have switches (or fets)  to disconnect them from each other so one cells leakage doesnt overcharge another cell.

[nctnico]

You need a BMS circuit to charge Li-ion cells safely. TI has chips for this purpose and (AFAIK) some are complete solutions which don't need an additional microcontroller. Still I think you will be much better of with a readily made pack which also adheres to the UN38.3 battery safety regulations. Without the UN38.3 certification you won't be allowed to transport your battery pack. Li-ion cells (especially the unprotected ones) are not something to toy with. They can easely push out hundreds of Ampere and cause a fire instantly. I have dealt with Li-ion pack design quite a lot in the past and the approval agency banished battery testing to cheap temporary buildings because testing is too unsafe to do in the main building.