I suppose you could pull the protection circuits off of a 10440 and attach it to a 10280. It would be ugly, add a lot of length, cost more than it should, and not have completely correct parameters for when to cut off, but it would be better than nothing I suppose. Probably.
li-ion discharge limit - 2.5v/2.7v/2.8v/3v???
- Thread starter Huz
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Mr Happy
Flashlight Enthusiast
This is not wholly or necessarily true. The discharge curve of a lithium ion cell is not linear. Take a look at a typical discharge graph like this one:
The top curve represents low rate discharge. You can see that once the voltage gets below about 3.5 V there is essentially no power left in the cell. Regardless of how low the Vf of the LED is, once the cell discharges to this point the LED will rapidly dim. The cell has no power left to sustain the voltage or deliver any current beyond that point. So it's really not important whether the Vf is 3.7 V or 2.1 V. As soon as the light dims, you should stop and change the battery.
MWClint
Enlightened
not without you noticing that your flashlight doesnt turn on or is pretty dim.
It would be instant indication that something is wrong and you should stop
using that light until you investigate it further. abused or old battery, short in
the flashlight electronics, damaged led..etc.
so in reality, if your light+battery have been operating like _normal_, and you just need to see if you need to swap batteries...testing the resting voltage
and seeing if it's above or below the 3.6v threshold is good enough.
Hope that clears it up.
DM51's voltage/capacity chart in the posts above is a nice quick reference.
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mdocod
Flashaholic
The lower Vf will result in a deeper discharge when dimming occurs compared to a "regular" Vf LED.
Given a scenario where a small unprotected cell must be used, my suggestion would be to just make a best attempt to prevent over-discharge by monitoring usage as best as possible. Just check the cell voltage before charging when you get back from your outing and see how you did. Keep track of the number of times that a particular cell is discharged to a less than desirable level (I'm going to call this less than 3.0V resting, between 3.0 and 3.5V is less than ideal but isn't the end of the world). Provided the cell is recharged within a day or two, I'd maybe put a limit of a dozen or less accidental over-discharges per cell then replace. Combine this with some voltage testing after coming off the charger and resting for a day or so to insure that the cell will hold charge voltage effectively. (ideally above 4.10V, when the cell will no longer hold above 4.0V it is effectively worn out). With some due diligence like this, I don't see a major problem. Alternatively, you might just make a habit of replacing the cells on a yearly basis or something to that effect (depending on how frequently the flashlight is used).
Considering the small stature of a 10280, the risk factor of having an undesirable "venting" event isn't much different than any other cell, but the intensity of said event on such a small cell would pose less threat. The difference between a 10280 and an 18650 is like comparing a 22 to a 30-06. Both weapons can kill and cause damage, both should be respected as dangerous, but we all know the underlying differences.
-Eric
Given a scenario where a small unprotected cell must be used, my suggestion would be to just make a best attempt to prevent over-discharge by monitoring usage as best as possible. Just check the cell voltage before charging when you get back from your outing and see how you did. Keep track of the number of times that a particular cell is discharged to a less than desirable level (I'm going to call this less than 3.0V resting, between 3.0 and 3.5V is less than ideal but isn't the end of the world). Provided the cell is recharged within a day or two, I'd maybe put a limit of a dozen or less accidental over-discharges per cell then replace. Combine this with some voltage testing after coming off the charger and resting for a day or so to insure that the cell will hold charge voltage effectively. (ideally above 4.10V, when the cell will no longer hold above 4.0V it is effectively worn out). With some due diligence like this, I don't see a major problem. Alternatively, you might just make a habit of replacing the cells on a yearly basis or something to that effect (depending on how frequently the flashlight is used).
Considering the small stature of a 10280, the risk factor of having an undesirable "venting" event isn't much different than any other cell, but the intensity of said event on such a small cell would pose less threat. The difference between a 10280 and an 18650 is like comparing a 22 to a 30-06. Both weapons can kill and cause damage, both should be respected as dangerous, but we all know the underlying differences.
-Eric
TooManyGizmos
Flashlight Enthusiast
MWClint ,
Thanks for your answer , it was a good one. It made me stop and think , why did I ask my silly question to start with. I was totally off in left field. My mind was in another place. I wasn't thinking about your original topic.
When you mentioned buying your digital meter , it got me thinking about just testing batteries laying around in a box. Not about testing one's you just took out of your light. In that case I can see your point , and the immediate reading just after use would be accurate . And useful to determine the amount of charge left .
It was not intentional , but my points were way off topic. I just wasn't on the same page as you . I'll bet you were wondering why I just didn't understand your question. Thanx for explaining and waking me up.
Next time I'll try to pay closer attention and not get side-tracked with my own thoughts.
.
Thanks for your answer , it was a good one. It made me stop and think , why did I ask my silly question to start with. I was totally off in left field. My mind was in another place. I wasn't thinking about your original topic.
When you mentioned buying your digital meter , it got me thinking about just testing batteries laying around in a box. Not about testing one's you just took out of your light. In that case I can see your point , and the immediate reading just after use would be accurate . And useful to determine the amount of charge left .
It was not intentional , but my points were way off topic. I just wasn't on the same page as you . I'll bet you were wondering why I just didn't understand your question. Thanx for explaining and waking me up.
Next time I'll try to pay closer attention and not get side-tracked with my own thoughts.
.
leukos
Flashlight Enthusiast
Good point, VidPro. High drain and low drain applications are often left out of the discussion when talking about li-ion cut off voltage even though this has a huge effect on the state of the battery and how effective protection circuits are. I would hazard to say that most protections circuits are designed for high drain applications. Running your protected li-ion down to cutoff with the low mode on your LED light is a recipe for battery death.
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