Arc4+ Li-ion protection question

Peter,

I have a question on how the Li-ion protection works...
You say that the arc4 will turn off when v drops below 2.75 to 2.5.
My question is, when does it detect the initial V to determine
what battery type? On reset or when the light is turned on each
time?

If it's when it's turned on each time, then that could be bad
because if the cell is already discharged to 3.0 it will take it
all the way down. This is what I suspect because I left the
light on over night to test this feature and woke up with open v of
1.0v yikes!

I believe it resets every time a new cell is inserted? I read it somewhere but I don't know if the source is correct.

7777, did that cell charge back up?

This was discussed multiple times and is also stated somewhere in the ARC FAQs I think, the light can only properly detect a Li-Ion when somewhat fully charged and then will use its intelligence to prevent overdischarge - when you remove the cell pretty empty and then re-insert it there is no way the circuit can detect it as LiIon but will think its a primary Lithium and subsequently discharge it to death.

Klaus

cy: yep - it's back up. 4.2v

klaus: I know... when you put it in at 3.0v there is no way. But that
wasn't my question. My q: WHEN does it detect the initial V?
On reset or when the light is turned on each time?

when it ran down to 1.0v. I never took the cell out.

As far as I know the official statement from Arc is that the initial V is detected every time you take away and restore the power to the circuit. This means when you change the battery or even unscrew the tailcap.

Perhaps you unscrewed the tailcap when the battery was around 3 V? This would explain why you didn't change the battery but your Arc ran it down nevertheless.

As far as I remember Peter once said that this was also a security feature. Let's say you need your light in an emergency very much for just short time but the detection cuts the power because the voltage has gone too low. Now you can unscrew the tailcap and screw it back on and just use this little power which is left in your battery. Of course you might damage you battery this way but in an emergency if your life depends on it this can be worth it

spacemarine: I'm pretty sure I didn't unscew the arc. I was testing
the security feature.

So at what point does the security feature kick in?
Say it kicks in at 3.1v. Maybe the last time I turned it on was 3.0v
and it had already determined that I needed to run it down all the way.

IHO, I think the security feature would be better activated from reset. That way you're not risking damaging your cell.

Actually if that was the case, it would just be detected as a
primary 123.

I'm going to do the test again - at the risk of damaging my r123.
in the name of science.
david