Eneloop Charging Rate

Using my BC-900 (firmware version unknown), what's the best charging rate to use to charge (4) AA Eneloop cells at the same time? Same question while charging (4) AAA Eneloop cells. I've been using 500mA, but have only charged them twice.

SilverFox will tell you to charge between 1c and 1/2c for proper end of charge detection and termination with any NiMh. So I charge at 1/2 the capacity of the battery.
1000mA for AA
500mA for AAA

My two yr old Eneloops still are remarkably consistent in performance.

Thanks and I'm assuming I don't do damage if I go lower, it just adds time to the charging cycle, correct?

Hello Ray,

The reason you charge in the 0.5 - 1.0C range is to make sure the charger gets a strong end of charge termination signal from the cell. When you charge at lower rates, you present the charger with a weaker signal. If the charger misses the termination signal, you overcharge the cell.

Overcharging = damage.

If you want to charge at a slow rate, charge at 0.1C for 16 hours. Overcharging at 0.1C is usually not much of a problem, however there have been some reports that the new low self discharge batteries are sensitive to any overcharging. If you want to do this, you may want to hedge your bet and set the timer for 14 - 15 hours when charging at 0.1C with these cells.

Tom

I've been using the 1000 mA rate with all my eneloop cells and they've been working great.

SilverFox said:

If you want to charge at a slow rate, charge at 0.1C for 16 hours. Overcharging at 0.1C is usually not much of a problem, however there have been some reports that the new low self discharge batteries are sensitive to any overcharging. If you want to do this, you may want to hedge your bet and set the timer for 14 - 15 hours when charging at 0.1C with these cells.

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Can you elaborate on the overcharging issue? This is fresh news to me. Does it mean that running a C9000 break-in cycle on LSD cells should be avoided or minimized?

There was a previous thread which addressed the charging of Slow Discharge NIMH cells.
https://www.candlepowerforums.com/threads/187884

According to Maha, makers of the Imedion SLD cells, a 0.1 mha charge for 16 hours should do no harm to the new cell, even if it has retained a significant factory charge before applying a "forming charge" to it. Good sense would suggest discharging the cell before doing this. However, Maha insists this isn't necessary. Although these batteries can be used right out of the package, Maha suggests running the breakin cycle initially for best battery performance. Will you have to do this breakin cycle again after 30 or so cycles as is suggested for conventional NIMH batteries in the Powerex MHC-9000 instructions? I would doubt it, unless the battery has been left idle for years.

i use 500-700-1000, they all work with healthy enloops, but 200, 200 is SOOO bad, it makes me wonder if i should put the charger on a UPS, because it will reset to 200 on a power outage (computer in it resets)

from my tests you can slowly overcharge a enloop in open air at 300ma for more than 100 hours without ruining it, using a constant non PWM method. in fact the cell displays MORE capacity after testing it, resting it and testing it again, even after charging it for the 100 hours. that test should give an idea that the enloops own charger should work just fine.

but in the 900 they totally baked at 200, hurt them worse than my torture test for some reason. they still are fine, but they got dang hot, and acted funkey for a while. (the 900 has less passive cooling than my test did, with its containment around the cells, and with the 900 the current is PWM Averaged not constant)

if i was making a recomendation of ONE setting, it would be 700, 200 is a disaster, 1000 is a bit hot, and 500 while it works ok, is below , and a cold room or a weak cell it could not terminate.

Thanks guys. It sounds like I should stay with the recommendations posted, as opposed to what I've been using.

1000mA for AA
500mA for AAA

this_is_nascar said:

... the best charging rate to use ...

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... is exactly the rate that is used by the Eneloop specific charger from Sanyo. I cannot remember what is was; probably less than 1A.
Anyway search for discussions about Eneloop charger.

BC900 is very good with termination. I haven't had a single miss yet, even when using the lowest 200 mA. So when charging reasonably healthy Eneloop cells any rate from 500 mA and higher is fine.

bob_ninja said:

... is exactly the rate that is used by the Eneloop specific charger from Sanyo. I cannot remember what is was; probably less than 1A.

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er, I think there may be a BIG caveat on that......

eneloop 4-position charger (original) -


eneloop 2-position charger -


This means the charging current for AA are either 300mA (0.15C) or 550mA (0.275C) -

So both the chargers are way off of the 0.5C to 1C, or 0.1C recommendations -
and more or less in the WORST possible range of charging currents -
according to whom?

BatteryUniversity.com page on nickel based batteries
about 3/4 down that page under
Charging nickel-metal-hydride -
" It is difficult, if not impossible, to slow-charge a nickel-metal-hydride. At a C?rate of 0.1-0.3C, the voltage and temperature profiles fail to exhibit defined characteristics to measure the full charge state accurately and the charger must rely on a timer. Harmful overcharge can occur if a partially or fully charged battery is charged with a fixed timer. The same occurs if the battery has aged and can only hold 50 instead of 100% charge. Overcharge could occur even though the battery feels cool to the touch. "

(Half a step back, eneloops although are LSD (Low Self-Discharge), are basically still NiMH, so the recommendations for NiMH applies.)

These charge currents were so contrary to all the recommendations that our local battery guru SilverFox singled out the eneloop chargers in his thread -

A look at slow charging

SilverFox said:

The questions remains, Why does Sanyo in the Eneloop site seem to contradict the recommendations in their main site? Perhaps the Eneloop chargers have changed from –dV termination to peak voltage termination. I think some testing may be in order…

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.... and people continue to wonder why I have issues/concerns with using rechargable cells and because of that, don't use them at all.

More fodder:

Duracell is imprinting this phrase on the wrappers of their re-badged Eneloop and their RayOvac Hybrid clone:

Standard charge 200mA for 16h

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Ya, the latest version of the standard Eneloop charger is whatever the cheapest thing the marketing folks at Sanyo could come up with to include in the package. NOT what the engineers would recommend.

Hello Bones,

I am shocked... Could you post a picture of that?

Duracell has taken the position that 16 hours is too long to charge a cell. They say, in their technical literature, that a cell can be fully charged (at 0.1C) in 14 hours. This is a major shift for them. I have had several "heated" discussions over this. It would be nice to have a little extra "ammunition" in my quiver for the next debate...

Tom

SilverFox said:

I am shocked... Could you post a picture of that?

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I can oblige with the picture, if I may:



The manufacturing code printed on the cell is 7F08 - L T, but I don't know how to interpret it.

Hold on, isn't "standard charge" a technical or historical phrase basically meaning a slow charge? It's been the "standard" way of charging a NiCd or NiMH battery since they were invented. That doesn't mean it's the best way to charge a modern NiMH.

Mr Happy said:

I can oblige with the picture, if I may:

...

Click to expand...

Many thanks for posting a most excellent photograph Mr. Happy.

Mr Happy said:

...

The manufacturing code printed on the cell is 7F08 - L T, but I don't know how to interpret it.

Click to expand...

It appears that your cells were manufactured on 2007 June 08 (7=Year, F=Month, 08=Day, LT=?).

On the back of American made packages of Duracells is a stamped date code. The first digit is the last digit of the year of manufacture. Next is a letter representing the the month, arranged alphabetically, A - L. The next two digits are the day of the month. The last letter represents the U.S. factory. Example: "4J08X" indicates Oct. 8, 1984 Gray market Duracells do not have a stamped code.

http://groups.google.co.ke/group/misc.consumers ...

A typical Duracell DL223A battery has a date code of 6J1313. The first alphanumeric character of the code is always a number representing the last digit of the year of manufacture. The second alphanumeric character of the code is always a letter, the position of which in the alphabet represents the number of the month of manufacture. That is: A represents January, B represents February, C represents March, etc. The next two alphanumeric characters of the code represent the day of the month of manufacture. Therefore, the date of manufacture for the date code 6J1313 is October 13, 1996.

http://www.acrelectronics.com/minib300 ... pdf

I have not noticed any private label Duracell products, but the date code they used ran something like this - last digit of year followed by a letter from 'a' to 'l' for the month followed by two digits for the day (of manufacture.) After the "use by" date appeared, this code disappeared, but I think they still use it on some products.

http://www.barc.org/1997/sparc jul 97 ... html

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I don't consider any of these sources definitive, but would suggest that if someone does locate a definitive source, they post it in its own thread for future reference.

Being able to narrow the search down to thread titles will offer some hope of locating it again.

Incidentally, I have a set of these re-badged Eneloops bearing the code 7K07-HT.

If this interpretation is correct, they were manufactured 2007 November 07.

Being less than four months old, I believe this makes them easily the youngest Eneloops thus far reported to be in the wild.

I suppose I should go change their diapers and devise an investment strategy for their college funds ...

Hello Mr Happy,

Thanks.

Tom

Hello Ian,

There are standards that the battery manufacturers use to determine the capacity of a cell, as well as the cycle life that can be expected.

These standards are under constant scrutiny and are occasionally revised. I can assure you that if a manufacturer was able to get better performance through a better charging protocol, it would find its way into the standard.

Duracell proposes a better charging protocol, but rates their cells according to the existing standards. If their better charging method was "better," I would expect them to show the difference in side to side comparisons. I have never been able to find that comparison. I would also expect them to market chargers that utilized their "better" charging method. When I run my own tests, their procedure seems to work for brand new cells, but falls short when the cell has been used for a few cycles. While their ideas on NiMh chemistry seem interesting in theory, then don't seem to prove out in actual practice.

Duracell is an excellent quality company and they have vast "expertise" in the primary battery field. I don't believe they manufacturer any of their NiMh cells. I am not sure if they do as much NiMh battery testing as the NiMh battery manufacturers do. Almost all of the information in their technical bulletin is very good, it's just this one part on standard charging that there are "issues" with. I have emailed them asking them if they could provide side by side comparisons that back up their claims and have received no replies from them.

Instead of "standing up" for their improved charging method, they label their product according to the existing standard. On one hand I am a little disappointed, but on the other hand I guess I already knew that their idea was a little "shaky."

Tom