AW Black Label 25540 reading 2.85 volts is it safe to recharge?

[Rommul]

I have 6 AW Black Label C cells that I basically never use. They have been sitting for about a year without being charged. I am recharging the others.

One cell reads 2.85 volts. Can I recharge this cell safely?

 

[Rommul]

I went ahead and charged it anyway and it was fine.

 

[45/70]

Yeah, that should be fine. The problem area is somewhere below 2.50 Volts. Some say lower than that. Most protection circuits trip around 2.50-2.75 Volts. It's not good for LiCo cells to be discharged to that low a level on a regular basis though. I realize this happened due to storage, but just the same......

Dave

 

[Rommul]

Yeah, that should be fine. The problem area is somewhere below 2.50 Volts. Some say lower than that. Most protection circuits trip around 2.50-2.75 Volts. It's not good for LiCo cells to be discharged to that low a level on a regular basis though. I realize this happened due to storage, but just the same......

Dave

The funny thing is when I tested the voltage of all the cells before charging and that one read 0.00 volts. I assumed the circuit was tripped so I popped it in the charger for a couple seconds to reset the circuit. Thats when I got the reading.

So I don't know if it self discharged down to that ~2.5 and then rebounded to 2.85.

As far as I know I only used that cell (I have them numbered) with a KL3 head but not for long anyway.

 

[45/70]

Well, in that case, It'd probably be a good idea to watch the behavior of that cell for a while. Protection circuits don't normally trip during self discharge. The current level has to be at some higher level, which self discharge doesn't possess. This is one of the less "protective" features of protected cells.

Since you're not really sure why the OC voltage was zero, before you put it on the charger for a few seconds, it's possible that the cell could have self discharged to zero Volts. As I said, protection circuits don't generally trip from self discharge.

If the cell doesn't seem to hold a charge well, or gets warm when charging, I'd consider it suspect and replace/recycle. My hunch is, you're probably OK though. Just keep a close eye on it.

Dave

 

[Rommul]

I plan to.

Thanks.

 

[flatline]

If the cell doesn't seem to hold a charge well, or gets warm when charging, I'd consider it suspect and replace/recycle. My hunch is, you're probably OK though. Just keep a close eye on it.

Dave

Out of curiosity, how warm is too warm? I have some 18650s I salvaged from a laptop that get "warm" near the end of the charge cycle. When I say warm, I mean about as warm as a sleeping cat's belly (only universal comparison I can think of...everyone knows how warm a kitty belly is :thumbsup.

Next time I'll get my IR thermometer out and measure them.

--flatline

 

[45/70]

Out of curiosity, how warm is too warm?

Yeah, "warm" is a subjective term. Let's just say they should never get "hot". How's that? The best way to put it I guess, is that a problem cell will get warmer than a cell that isn't in question. So, the best way is to compare a questionable cell to a known, similar, "good" cell

Whether a Li-Ion cell gets warm or not, has a lot to do with the condition of the cell, and the charger being used. Older, well used cells, for example, will usually warm up a bit when charging.

The type of charger used makes a difference also. When a hobby charger, which uses the proper CC/CV algorithm, is used with newer cells, the cells will remain pretty much at ambient temperature. With older cells, there is a just detectable, increase in temperature.

When a CC charger such as the WF-139 is used, especially older cells, will get warmer towards the end of the charge. This is because this type charger is actually "forcing" current through the cell, until a predetermined voltage is reached. A charger using a proper CC/CV algorithm will terminate the charge when the current drops to a certain level during the CV stage, and thus prevent the cell from heating up.

So again, the best way to determine if a cell is getting "too warm", is to compare it to a similar cell (same brand, type, age etc.). And for sure, they should never actually get "hot". If they do, your running the risk of a incident.

Dave