In going through these great postings, I saw something which got me wondering:
Is there a 26650 rechargeable flashlight that will not charge AAA batteries?
I did not even consider this as a safety issue. So, just inquiring.
Most CC/CV chargers (really any of a very few charging ICs) have a maximum voltage of 4.2V.
So if the cell is at 3.0V and max current is 500mA, it’ll apply, say, 3.01V so that the current maxes out at 500mA. Voltage of the cell will rise as it charges.
Once the applied voltage hits 4.2V, it maxes out and stays there, letting the current trickle down and down as the cell’s internal voltage rises to 4.20V.
When the current drops down to about 10% of the charging current, so in this case 50mA, charging stops.
Point being that 3 AAA cells should be 4.5V open circuit, but really dead ones might be only 1V each or 3V total.
3V from a dead Li-ion cell, or 3V from a LFP cell, or 3V from 3 alkaleaks, all look the same to the charger. There’s no (easy) way to tell what’s what. It’ll just happily apply up to 4.2V or up to 500mA until The Cows come home. And The Cows haven’t been out in a looooooong time so they won’t be home anytime soon.
There might be some NASA-level charging ICs that sense internal resistance, have timer circuits built in and monitor changes in voltage/current, etc., and might deliberately crap out if cooking for too long with no change, etc., but cheapie chargers likely won’t have any of that.
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This is one of those “just don’t do it” scenarios, Lightbringer is correct, no charging IC inside a light can detect the difference between 3xNiMh or 1xli-ion.
I’m not aware of any quality lights that come with a 3xAAA adapter. Outside of having to use AAAs in an emergency and no alternatives available, the 26650 cell is far superior, I’ve no idea why anyone would want to use AAAs.
If you’re using a light with built-in charging, and you’ve an adapter you’ve sourced somewhere else, then any mishaps are on you.
Charging NiMh in series isn’t great, differences in internal resistance in the cells results in mis-matched charge rates…
I mean, if you deliberately trying to stuff things up, no one will stop you LOL. It’s like, what if I drive my car up a wall? With today’s technology you can and you will damage your car and your wall.
Or they could be smart and put a diode or MOSFET anti-reverse circuit into the AAA adapter so current can only go out not coming back in. But it’s just a lot of trouble for some marginal case of deliberate damage so I doubt anyone would bother.
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Like the guy who tried running nitromethane race-fuel in his daily driver and fried his engine.
It would not be my intent to put AAA batteries in a 26650 flashlight except in the utmost of emergencies…as I will have 26650’s as spares.
But I could see how someone ignorant/forgetful could mistakenly try to charge the flashlight after using the AAA batteries.
Then leave it to the insurance company to pay to rebuild your house.
Just kidding.
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Just stop using alkalines outright and use NiMH cells, they will charge in the holder just fine (and can’t really be overcharged anyways), albeit not to their full charge voltage as they’re 3S 4.2V nominal instead of 1S 3.7V nominal.
I am familiar with “someone”. My younger brother once told me:" leave me alone and let me make my own mistakes". Didn’t have to wait too long.
BTW: you just showed us the advantage of having a separate charger. No assuming, only observing.
I have actually managed to melt one of those AAA holders when I put it on my M3-C with Eneloops for the lulz. A few seconds of turbo and the light stopped turning on. When I removed it to inspect it one of the spring had deformed permanently and stopped making contact so I guess it failed relatively safe?