I reworked my low volt cutout for buck-puck.. i have photos online here
I have a detailed writeup in this post
a picture of the circuit is here:
Anyhow.. the reason for posting.. i see entirely too little discussion of how people protect (meaning.. likely they don't). their NIMH and far more important LION cells from over-discharge.. fortunately at least a lot more LION cells are like PILA and have the low-voltage cutout built right in.. but more and more i read about people making NIMH or RAW LION solutions that use boost or buck circuits like fatman or buck-puck and they don't include a provision for low-voltage cutout.
You absolutely 100% can not rely on visual feedback (i.e. light dimming) to know when the batteries are dead.. if you try this.. the very first time you see dimming you just permanently damaged your battery pack.
So.. for my first big flashlight mod. over 3 years ago.. the megasonic i immediately recognized the need and built a LVC (low volt cutout) circuit..
Well just yesterday i finished re-working my brother's tri-lux drill-lantern 9W light.. it use 3x Lux3.. it actually probably is closer to 10-11W at the emitters from overdrive.. and i used the low-volt-cutout chip that i now use for the hotdriver (in-fact i cut a hotdriver board down to use as many of the traces and pads as i could)..
In any event.. i know this is something that modders should be clamoring for but i don't hear much about it... are people just wrecking their batteries w/o realizing it or are they using protected LiONs, or just 'living on the edge' and trying to recharge enough they don't hit the 'just hurt my batteries forever' limits of NIMH or LION?
I'm considering making a tiny little circuit like the one shown above.. it would be easily adjustable to monitor *any* battery voltage above 3-cell NIMH or 1cell LION (this example is a 20-cell NICD).. i would be able to sell them for $10 i think.. (not meant for 'making money'.. but as a help to the modding community to make safer, better flashlights.
Under moddest or high power.. NIMH cells are kaput at 1.1V.. and LION are kaput at 3.45V.. most factory cutout for LION is about 2.5V which is the absolutely lowest recommendation.. and NOT good for longevity of the cells.. a much nicer guideline for shutdown is 3.0V for LION and 1.0V for NIMH or NICD.. (though NICD are tougher to deal with low-votlage.. it's said they can handle being discharged to zero).. I don't use NICD, ironically this particular circuit was made for a NICD powered device.. I don't believe in discharging NICD to zero especially when in series and especially when TWENTY CELLS..
So.. any interest in such a device? if i get even 10-15 interested parties i could rationalize making a run of the chips.. There is a $50 surcharge on 'tiny boards'.. and the boards would probably only cost like $1.50 each... if i buy 200-300 of them.. but maybe $2.50-300 each at 100 qty.. so i do need to see some interest before i can make a batch... For now i can reproduce the hack i just did without too much difficulty.
I would make the circuit capable of applying either a TTL high or TTL low to a circuit when low-voltage is reached on the battery.. you can use that ouput to control the likes of fatman (has a shutdown-pin).. or buck-puck.. has a high-volt = dim 'control pin'.. most switcher chips including the one in downboy, etc. have a control pin that could be activated (usually they are jumpered 'on' unlike fatman which has an actual connection on the board for it!).
The circut would be a bit bigger than mine shown above.. but still on the order of 1/4 x 1/2 inch.. to include the extra parts required to do the optional Vhigh for low-volt.
Thanks for your feedback.