Questions on building a lithium battery pack with pcb? Answered
I have to build a pack to run my portable N64. I have some experience building with NiMh and NiCad, but I havent built a li-ion yet. Ive done my research but would like some feedback before I start building.
18650's - 3.7V 3600mAh ea
7.4V PCM for 18650 Li-Ion/ LiPo
7.4V Li-ion/LiPo charger at 1.2 Ah
Either to build a 2S2P pack or a 2S4P pack. Currently the N64, 7" TFT LCD, Controller, and Audio amp w/ 2x 8Ohm speakers is consuming just over 1A from what i can tell. its running off of a perfboard w/ regulator and rail, thats hooked up to a universal transformer that is set to 7.5V 1A. Everything works but when I turn the volume up it cuts off and then powers back on. I dont know any other way to find out the over all power consumption. I cant just look up all the specs because the LCD is from china and i dont have any specs.
Anyway, back to my plan. obviousely I want as much run time as i can get out of it with out compromising weight and space. all componants of the portable can run off of 7.4V or lower, to include the lcd even though its rated at 12V. it can run as loas 6.5V.
I have been debating between the 2S2P which should yeild 7.4V 7.2 Ah, and give me a runtime, some where in the ball park of 4 hours.
or a 2S4P which should yield 7.4V 14.4 Ah. It would only be slightly more space and provide approximately 8 Hours+
Thats if I am even calculating everything right
Ok, Regardless of whether i run a 2S2P or 2S4P the connections to the Protection Circuit will be the same, Right?
Pos --> B+
Neg --> B-
+ to - ( Between Series connection) --> B1 or BM
I understand that Li-Ion are safer when it comes to balancing then LiPo, but is this right? having 2 parallel cells or 4 parallel cells connected with the only balance connection between the series. I just want it to be safe.
Next is the charging. I bought a cheap smart charger for 7.4V 1.2A output. Will it matter whether i build the 2S2P or 2S4P, or will it work for both. I know it will obviousely take twice as much time to charge with the bigger pack, but is their a max number of individual cells that a PCB can handle, or does it only matter the overall voltage?
I also Included in my diagrahm a setup for a DPDT switch to change between pack powered, wall powered and battery charging. I want it to have an "ON" and "OFF" setting. while off, pack is disconnected and if wall charger is plugged in, it will charge the pack. while in the "ON" position, pack will power the device, but if wall charger is plugged in, then it will run off that.
Can I even use a wall charger for the Li-Ion pack to power the device, or will it not work.??