Part 2 of my Dive light build.......the battery!
Going for a 3S5P setup of ~2500mAh 18650's.Could possibly go 3S6P for extra beans?!
What battery protection circuit/s could i use for this setup? Charge balancing?
Will also need to build/buy a charger.
3S is 3-cell, so any 3-cell protection circuit that delivers the amps you need to run your torch. If it's an LED then the amps re reasonably predicable. If it is a HID torch then there's a current draw spike during start-up that could be as high as double the rating of the ballast. Only HIDs will you need to know the max current allowable as all the common PCB will alllow for typical LED draws.
You don't live in the US so I would steer clear of Powerizer/Batteryspace.com. Their international postage is outrageous. Use Batteryjunction.com or Fleabay to source your PCBs.
If you plan on using an 'intelligent' battery balance charger (and I recommend you do) in concert with a driver that monitors voltage and has a programmable cut-off function (like Taskled drivers), and you don't plan to use the battery for any other device, then you can get away with not even needing a PCB. The charger is designed to prevent overcharging, and the driver will prevent over-discharge. Unless it floods the current draw will be fixed by the driver. But, having said that 3S PCBs are cheap as chips and readily available so I recommend you install one regardless.
With high power draws and over time your battery will probably start to become unbalanced. using a smart charger and having individual leads coming off each cell to a JST plug will let you balance while charging. A balanced battery will give you maximum capacity (glow time) potential.