Possible BC-900 charger not terminating correctly

[Flatshovel]

Ok, I have a question. I have a BC-900 charger that I was charging up some 2400mah lsd Imedions on today. I think the charger is not terminating correctly and wanted to get the thoughts and opinions from this forum. When I started the cell voltage was 1.16 I set the charger to charge at 1500mah which is just a hair above 0.5c rate, the cell voltage got to 1.54v and display was reading 2.2ah and was still charging. The batteries never got hot just warm at charging at this rate. I only charged up 2 AA batts in slots 1 & 4. I stopped the charging when the capacity hit 2.2ah not wanting to overcharge them. I thought battery voltage when full would show about 1.46-1.47v. Since the voltage went up to 1.54 did the charger miss the signal? Just wondering?

Thanks,
Joey

 

[moldyoldy]

well, hmmm, maybe some more info would help; How old were the cells? How deep was the discharge - which at 1.16v appears to a total discharge ? Did the light shut off, or give a low-voltage flicker or simply become very dim?

In my experience, new cells have a slightly greater tendency to behave differently than after a few cycles. ie: a missed termination. especially if the cell was only slightly discharged.

However, since you stated that the cells were not getting hot, I suspect that they had not reached full charge yet. A full charge on a cell is somewhere from 120% to 140% of the mah rating. IOW, if the cells were rated at 2400mah and the charge input was only 2.2 Ah, then the cells had not reached full charge.

Nevertheless, based on my experience with a few copies of the BC900, I would not want to charge any cell at the full rate of the BC900 charger to charge completion. I would use that charge level only for a interim quick charge with no intention of allowing the cell to complete a charge. Why? The BC900 has had too many problems with high-rate charging. I had more than a couple cases with the BC900 on a charge rate of 1A and higher where the charger shut down charging to a slot. meaning it was too hot. that is not good for the cells, if not the charger also. On the BC700 I rarely use the 200ma rate or the 700ma charge rate. My normal charge for an AA cell is 500ma on the BC700. I might run the BC900 up to 700ma charge rate. However the 1000ma charge rate for 4 cells packed tightly as in the BC900 causes them to become too hot.

 

[Yamabushi]

The Sanyo Eneloop product datasheets show peak voltage before -dV at approximately 1.57V when charging @ 40°C ambient, 1.61V when charging @ 25°C ambient, and 1.68V when charging @ 0°C ambient. I don't know if Imedions would be similar but it appears that 1.54V isn't particularly high. You probably did not reach full charge.

 

[Flatshovel]

Thanks for the replys, ok so it sounds like the batts did not reach full charge. I will do another charge on them and see what happens this time. In reference the cells they are only about a year old with about 30-40 charge cycles on them. I use them in a scanner radio that I have and the low battery icon came on so I pulled them from the unit and charged them up. I think I will run a discharge cycle on them at 500mah and charge at 1000mah and see how they do overnight. If I charge at 1000mah this will be just below 0.5 rate for them, I don't really know if I trust the BC-900 with 3 cells in it charging at 1000mah. Seems like the charger does get hotter than one would like. I have thought about making a custom battery holder to charge the cells in, I know by doing this I will be bypassing the temp sensors but I think I will be ok anyway. The main goal is to see if the cells get hot when spaced apart. This way I can tell if all the heat is coming from the batts themselves or mostly from the charger. What do you think?

 

[moldyoldy]

a separate battery holder for charging? eh, then the charger electronics have to deal with a voltage drop in the connections which could mess up the -dV/dT sensing. If the goal is to reduce heat, then simply prop up one end of the charger an inch or so. A rubber eraser on it's side is sufficient and does not slip. That helps. Yes, under a 500ma-700ma charge rate, the cells will become noticeably warm if not mildly hot. that is as expected.

BTW, I use the IR sensing temp readout from Radio Shack for about $20.

 

[apagogeas]

A battery at 1.16V resting (normal fully empty considered around 1.2V) is practically fully empty so you can pump in all the available capacity it can accept. If the batteries are in good condition and can possibly accept 2.2-2.3Ah charge, you just didn't fully charged them, at least this is what I understand from what you posted. Chance for a missed termination with such a high current seems very improbable really. Also being warm with such charge rate again means not fully charged.