Is an MP7 used with (1) CR123 Safe? or should I only use the 18650?
Well the
specs for the Titanium 123 from battery junction show (picked because it's the first discharge rate google found for me)
Max. Constant Current 1500mAh
Max Pulse Current 3000mAh
PTC High Current Discharge Protection 5AMP
Silverfox did do 2A draws on cells in the 123 shootout including the titanium. He mentions that 123's get hot at 2A. That's one more heat source in a small light. Put it together and I wouldn't want to try and pull 2.8 amps.
Except this module is direct drive and probably can't pull that much. Looking at the P7 spec
sheet typical Vf at 2.8A is 3.6 - more than the cell provides unloaded. Typical Vf at 1.4A is 3.3 - so exceeding safe current also requires more voltage than an unloaded cell provides. Good news.
Voltage will dip under load too. Looking at the
battery shootout it drops just under 2.5 volts with a 1.5 safe amp draw. Typical forward current at 2.5 volts is a big fat zero - no light but no

. At 3 Volts you get forward current that's maybe 400mA. Even at that draw the cell won't maintain 3 volts though. So with a typical Vf you are looking at less than 100ma per die. You would need a very low VF LED to push the max draw limit.
It's
probably safe (I'd check tailcap draw the first time I did it as an indirect check for low Vf). It's probably not going to be as bright as a cheaper M30 with a primary though. A primary might make a backup but I wouldn't buy this to use with one. If you really want a 1x123 form factor with this module think IMR 16340. :thumbsup:
Disclaimer - I assume no liability. Proceed at your own risk. I make no claims of accuracy or actual safety. I am frequently wrong about anything and everything. Anything I think might be safe could actually result in immediate apocalypse. You should investigate reference material on your own and make your own judgement. Red Ryder BB guns will "put your eye out kid."