Unprotected LiCo cells.

peter yetman

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I probably don't want to hear the answer to this this question, but here goes.
I have about a dozen AW 18650 2600mah cells qhich I've been using for a few years.
The protection circuits have failed on a number of them so I removed the cicuit, rewrapped and carried on using them. Since then I've removed the boards on all of them to avoid getting caught out in the dark.
I'm treating them with care, as I would an IMR cell, as regards over discharge over charge etc.
My worry is, are the LiCo cells inrinsically less safe than IMR cells?
Shpuld I dump them before they dump me?
Thanks for looking.
P
 

Dr. Mario

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As long as you use it in the flashlight with Low Voltage Protection with the cutoff of about 3.0 - 3.5 Volts. The game is to NEVER let them go below 3.0 Volts, and doing so preserves the Lithium Cobalt battery lifespan, as they're quite sensitive to everything. You don't have to dump them, so long they never have went under 3 Volts - but if one of them have gone under 3 Volts, discard them - not worth having one blow up in the charger. Yes, Lithium Cobalt batteries are much more dangerous than IMR ones, but as long as you use the common sense, they won't go nuke - some tolerate abuses better than the others, especially Panasonic ones.

I also hope you have decent charger (ie. not a dumb charger as Lithium Cobalt batteries just go KA-BOOM when overcharged, which is also a common sight in RC hobby).
 

peter yetman

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Thanks Doc, that's reassuring, and yes I have a decent charger.
I will now ask a supplementary question...
My main light is a Direct Drive XM-L2 which runs fine on the 18650 LiCos. It draws about 2.5 amps. If I use a High Drain IMR it draws 3.5amps, enough to burn out the emitter.
Presumably the industry is going to go over to High Drain cells sooner than later, what unprotected cells will I be able to use that will restrict the current?
For this light I don't want a driver, it's my minimalist, super simple, nothing to go wrong light.
Thanks all.
P
 

magellan

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I agree with pretty much everything said here, but I think the most interesting thing is how you modified them yourself. :)
 

archimedes

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Hey P, with direct drive, to drop the current, you'll just need a resistor

( I'm sure there must be a diagram of this around here somewhere :D ... )
 
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Dr. Mario

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Well, sometimes simple can be a bad thing. Why? Lithium Cobalt cells are quite fussy so LED driver with battery low voltage cutoff is mandatory with LiCo cells for obvious safety reasons. If you like to play with fire while remaining safe, you will need to have DMM, that way you don't accidentally run it down so low.

For direct drive LED flashlight, I'd recommend to stick with LiFePO4 or IMR cells for obvious reasons.
 
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peter yetman

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For direct drive LED flashlight said:
Which bring up my supplementary question, are there any IMRs which restrict the current delivery to around 2.5 amps?
Thanks for all this help, I do appreciate it.
P
 
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Dr. Mario

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It's a bit tricky, as it depends on a few things. First, any Lithium-ion batteries don't really restrict current; Ohm's Law determines the resultant current. However, it also depends on the state of charge of the given cell at the moment as the LED forward voltage affects the total current consumption owing to internal resistance of both the LED and the battery in use, sans the wiring resistance (which is of course unavoidable).

Second, LED also affect the current consumption at given temperature, as the LEDs and almost any high performance diodes act like Negative Temperature Coefficient (NTC) thermistor, meaning the warmer they get, the lower the semiconductor junction resistance will be. Hence it's recommended to use the resistor to keep things manageable.

But, if you're really confident in attempting direct drive (there's such software-defined direct drive LED drivers that exist anyhow), I'd recommend to have the direct-drive LED in a well-heatsunk LED flashlight host such as Convoy L2 to keep the resistance of LED manageable so you don't accidentally cook the whole thing.
 

peter yetman

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Thanks Doc,
I guess I'll see what happens, I'll carry on using my DD module with the LiCos and when they start dying I can rebuild it with a resistor or something else may have come along by then.
Thanks for the chat.
P
 
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