Charging Unprotected 14250s

[KentuckyMike]

Hey everyone,

I've adopted a Raw NS as my new pocket light. Its use brings up a few questions about unproteced 14250s. I apologize if these have been asked before, but I'm having trouble searching at the moment, and surfing came up empty.

1) What should be considered the lowest voltage the battery should be allowed to go (to avoid damage)?

2) Same as above, but rather than to merely avoid damage, to also maximize cycle life,

3) Is the 4.12v I'm getting from the Nano ok? Should I pull it off at 4.11 or 4.10? Could it be allowed to trickle a touch higher without damage/danger?

4) Would daily charging (often shallow discharging) harm cycle life, or extend it?

I know the normal advice is, "as soon as you see a drop in output, pull it and juice it," but in my situation this is difficult. I use the light for various tasks in various levels of ambient light throughout the day, and on low for 3-10 minutes a night to check on animals and get to bed at night (with a burst of high at the top of the stairs to make sure the door downstairs is secured). I use it in such short bursts that I don't see an output drop, and I think the drop could be days in coming at times. (Tonight, for example, the cell reads 4.03v on the DMM, and it was charged to 4.12 fresh and 4.11 rested last night. That is from last night's ritual and a bit of use, and a touch of showing off, today.)

I want to keep a good charge, because I may need to use high heavily one day, but I also don't want to sacrifice cycle life. And it seems mistakes in charging/discharging would be magnified in such a small cell. Would working with two batteries (switching each night to extend time beween charges on each cell) help at all?

What do you think? Thanks in advance!

--Mike

 

[SilverFox]

Hello Mike,

There are two voltages to look at for discharging. One is the voltage under load. That voltage should not go below 2.5 - 3.3 volts, depending on the current draw and the cell construction. 3.0 volts is a good compromise to shoot for. The other voltage is the open circuit resting voltage. After the load is removed and the cell allowed to rest for a few minutes the open circuit resting voltage can be measured. Anything below 3.5 volts is over discharged.

You can get good cycle life by limiting the discharge to 80% of the cells full capacity. If you normally get 1 hour of runtime, limit the runtime to 48 minutes.

The maximum voltage during charging should be 4.2 volts. Charging to that maximum is supposed to give you around 500 cycles. If you limit the charge to 4.1 volts, you can increase the cycles to around 1500. The cost of this increase in cycle life is less capacity and less runtime.

I always recommend frequent charging with Li-Ion cells.

You didn't mention anything about storage. If you are not going to use your light for a few days, you will get better cycle life if the cell is stored at 40 - 50% full.

Tom

 

[KentuckyMike]

...After the load is removed and the cell allowed to rest for a few minutes the open circuit resting voltage can be measured. Anything below 3.5 volts is over discharged.

You can get good cycle life by limiting the discharge to 80% of the cells full capacity. If you normally get 1 hour of runtime, limit the runtime to 48 minutes.

The maximum voltage during charging should be 4.2 volts. Charging to that maximum is supposed to give you around 500 cycles. If you limit the charge to 4.1 volts, you can increase the cycles to around 1500. The cost of this increase in cycle life is less capacity and less runtime.

I always recommend frequent charging with Li-Ion cells...

Hey Tom,

I'm currently charging to the 4.12 (fresh off the charger), so I'm pretty satisfied there. I always try to pull it as soon as the light changes (well, it normally goes from red to orange, hangs at orange for 5-10 minutes, then green, so I wait until it's solidly green).

The other hard thing for me is the light is used for a minute here, 20 seconds there, throughout the day. It gets difficult at best to keep track of total runtime. High runtime is no more than 18 minutes, low runtime is around 6 hours. The light will probably never go more than 20 hours without at least some use. If I charge to 4.12v, I should have at least 500-750 cycles, which means I could charge the cell each night and just replace it once per year just to be safe (cheap insurance, at $4.50/year). This may be the best compromise until the protected 14250's finally (hopefully) come around.

Thanks for your time and expertise!!

~~Mike