Charging rate for eneloops

About: 0,4C

llmercll said:

Why do so many people recommend charging eneloops at .5c or about 1000mah while the official eneloop chargers do it much lower at 200-300mah?

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Very generally, many chargers detect charge termination better around .5 to 1C, and heat in the cell at this current isn't too much. I can't speak for the official charger design, but the low current could be cheaper to design, and reduced heat in the cells leads to longer life. But charge termination detection could be worse, and it takes longer to charge.

4 bay chargers sometimes drop current output because it maxes out at 1/4 total per cell and with 4 cells it requires 4A to be regulated total.
I personally have no problem with 0.25C on chargers and batteries that I know are good, that is about 200-300ma for AAA and 500 or so for AA cells as I've had no problem terminating charge on chargers I have doing that. For less healthy cells a higher charge rate will help some chargers terminate properly while others may just sit and cook cells till they (hopefully) time out.

Do the "official" chargers change current for AAA vs. AA? That would be one rationale, same charge current for both, cheaper design.

Most people like fast charging, too.

From what I've read, the ideal method of terminating charge is the -dV/dt method. This is where the cell voltage actually drops a bit as the cell reaches full charge. This is difficult or impossible to detect at charge currents below 0.5C, so in order to do this you need to charge at 0.5C or higher. Done properly, you can charge pretty quick and with relatively low heat.

Unfortunately, I had quite poor luck building a charger to do this, specifically with 3S1P Eneloop AAAs. It kept detecting drops in the voltage well below full charge. When I increased the threshold a little, it started missing the real one and overcharged cells. I ended up going with 0.1C/16H charge and everything seemed okay. Never ran high cycles on them this way though.

DIWdiver said:

From what I've read, the ideal method of terminating charge is the -dV/dt method. This is where the cell voltage actually drops a bit as the cell reaches full charge. This is difficult or impossible to detect at charge currents below 0.5C, so in order to do this you need to charge at 0.5C or higher. Done properly, you can charge pretty quick and with relatively low heat.

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Actually, the proper method for terminating the charge of NiMH is not -dV/dt, it is 0 dV/dt. The voltage drop is caused by the excessive heating of the cell upon entering overcharge. Most chargers use -dV/dt for the only reason that it is easier (read cheaper) to implement. Small voltage drops (2-5 mV) do not cause that much overcharge and overheat at currents of the order of 0.5 C. However, most chargers don't measure voltage with such precision, and terminate on -dV of 10-20 mV where the temperature rise is significant.

Regarding the charge rate of Eneloop chargers, the reason of charging below 0.5 C is cost again. These chargers usually divide the current between channels by the means of cycling through the channels at constant current. This is the cheapest way to design them. Then, there are the dumb chargers (Panasonic calls them basic) that charge at about 0.1-0.2 C with a timer. These are to be avoided at all costs.

i use my c9000 which defaults to 1a.fine for aa.
aaa i set to 500ma.
they seem to be easier to damage at too high charge rates.

Eneloops...
AA... 1000 charge, 500 discharge
AAA... 400 charge, 200 discharge
Maha Powered folks recommended this to me years ago. Eneloops lasting and holding charges a very long time.

snakebite said:

i use my c9000 which defaults to 1a.fine for aa.
aaa i set to 500ma.
they seem to be easier to damage at too high charge rates.

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I have several chargers..... A Duracell mobile charger that I mostly use for nimh and it works fine even though it is only 500/300ma for AA/AAA I've never had a cell not fully charge on it or give a blinking error if it is bad. I have a Lacrosse BC900 that is one of them that works fine without nuking the world that I can adjust charging rates plus an old rayovac 1hr charger thats shuts off at 1800mah but you just have to reinsert the batteries again to finish the charge. This charger pulses cells in a way that bumps up the voltage high enough for the other 2 chargers to "see" it from low voltage to 0 volts.

snakebite said:

i use my c9000 which defaults to 1a.fine for aa.

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Same here.

I've been charging my AA Sanyo Eneloops
in my Maha C9000 (and now C9000 Pro)
for the past 14 YEARS now !

At least once a week,
and they still do their job nicely !

:twothumbs


So no need to worry, methinks . . . . .


_

Methinks you are correct, @Burgess, been doing the same with the same result as yours. :-D