After almost 3 years of ownership I have finally busted out my C9000 and Eneloops. Never really had a use for them until I bought a Zebralight headlamp, one of the few lights that really shines on Eneloops. Lithium Ion still kicks tail though. What charge rate will treat my batteries the best?
.5C for whatever mAh cell you want to charge
0.5C is close enough to 1000mA. This also happens to be the default on the C9000 which makes for a minimum of button pressing if that's important to you.
(FYI, there have been a few discussions about how much "trouble and effort" is needed compared to other brands of chargers. I don't really see it personally, but.....y'know how some people get)
If you want your cells "fully" charged it is said you should leave them in for about 2 hours after DONE which tops them off with approx another 100mAH.
I go with 500mA, there is no official best charging level for NiMH, some can take more then others, but i find 500 is a good balance between charge time and how hot the batteries get (you should try to avoid overheating them)
Sometimes a charger can have problems determining end of charge using -deltaV if the charge rate is less than 0.3C.
You may not have these issues with the C9000 but personally, I'd consider 500 a bit low. As long as you're not in the middle of a heat wave you should be fine going a bit higher.
Maha recommends a minimum of .33C for a lesser chance of missed termination. That’s about 700ma in the case of the 1900mah AA Eneloop.
i’ve never had a problem with an eneloop, now other batteries are a different story, duracell 2650s will terminate in a few minutes (even if empty) if anything over 200mA is used for charging
certain rayovacs will get too hot to hold if done at 500 or higher (1500mA cells i believe)
hmm.... Older cells with a higher resistance perhaps? Do these cells also crap out if you try discharging them at a high rate?
Interesting that they are not quite bad enough for your charger to reject them up front. Have you ever noticed how the initial check reads on these compared to your Eneloops? Close to 2V perhaps?
the duracells charge fine at 200mA, self discharge to nothing within a week, i don’t use them for anything, they are headed for the recycle bin, they have less then 10 actual uses on them.
the rayovacs are fine charged at 200mA, discharge in a few months if not used (not lsd), and work well in low draw situations, i use them in 1 watt lights
both came to me new and behave the same now as they did then
what do you mean by rejected by charger and initial read at 2V?
There are recommendations from manufacturers and according to them 500mA is to low.
I have had problems with a C9000 and Duraloop AA. I like to charge at 1000 ma with the charger connected to a 3 hr timer. I have witnessed the charger missing the cutoff and pushing as much as 3700 mah through good cells.
I have some old Uniross and Philips non-LSD that none of my ‘intelligent’ chargers will charge. They get really hot in a low current dumb charger, and won’t hold charge for very long.
Charge by half the capacity.
Eneloop AA - 1000mA
Eneloop AAA - 400/500mA
Does that apply to 10,000 mAh D cells? That'd be incredible.
The .5C charge and .25C discharge rates apply to AA and AAA cells. The Maha D cell charger C-808 has 2A as a “Fast Charge” mode already, with normal rate at 1A I think, so I guess it does not apply to D cells. I have posted this question regarding why D cell niMh have different charge/discharge recommended rates compared to AA and AAA cells and so far no one has sufficiently explained why is it so.
From Maha 808M: https://static.eleshop.nl/mage/user-manuals/mh-c808m-manual-en.pdf
• Do not charge battery cells other than NiMH or NiCD. AA, C and D
batteries must be able to accept a 2.0A (Rapid mode) / 1.0A (Soft
mode) rapid charge current. AAA Batteries must be able to accept a
0.7A (Rapid) / 0.35A (Soft) rapid charge current.
• Do not use one-hour rapid charge mode on AA / C / D batteries rated
under 2000mAh and AAA batteries under 700mAh. To charge them,
use the Soft Charging mode (refer to “Soft Charging Mode”).
Appropriate Charge Rate for NiMH :
I am charging some older batteries and see that the charging capacity is much higher than the capacity I programmed. Why doesn’t the charger terminate correctly?
The charger terminates by voltage and by temperature simultaneously. For certain older (and low quality) batteries, they do not produce the proper negative delta V signal (a small voltage drop at the conclusion of the charge) needed for the charger to stop. At the same time, the battery temperature failed to reach the termination limit as the charging rate was probably too low. To address this issue, you should attempt to perform a BREAK-IN mode on the batteries first. You should also use a higher charging rate.
When using higher charging current, the charging capacity seems to reduce. Is this normal?When charging at higher current, the charge completeness reduces thereby lowering the charging capacity. This is to prevent batteriesy overheating. This typically occurs at a rate greater than 1500mA. Generally speaking, 1000mA achieves nearly full charge completeness for AA batteries. Even after the charge ends (DONE appears on screen), the charger will apply a topoff charge and continuous maintenance charge. Even though the capacity on the screen is not increasing, the batteries are being topped off. If you would like to achieve better charge completeness at higher currents, a small fan can be added to cool the batteries externally.
Why is it not recommended to charge battery below 0.33C?
When charging below 0.33C, the batteries may not produce a sufficient end-of-charge signal for the charger to terminate correctly. Although the temperature sensors will safeguard from batteries overheating, a lower charging rate might not produce enough heat in the batteries to trip the sensors. If a low charging rate is desired, you should use the BREAK-IN mode. Charging in that mode is terminated by only time (1.6 times battery capacity) and temperature.
I'd guess it's that it's because it requires a hobby charger, and who wants to risk damaging such an expensive cell without absolutely knowing it's safe beforehand? At least I'd be very wary about charging at 5A.
Oh, but I have tried charging my Imedion 8500mah D cell at 4.5A using my iCharger and it went through it like an AA cell!
When you first begin charging, the C9000 will do an initial internal resistance check and show you the result as a voltage displayed momentarily on the screen. If it reads more than 2V the charger will usually reject the cell with the message HIGH displayed on the screen.
I've even had some really bad cells display the message MODE or simply flash and begin again as if another cell had been inserted.
If you haven't noticed this pre check before, try inserting just one cell into the unit and select a charge rate of 1000 mA. You should see a voltage displayed for a short period of time before the charger either rejects the cell or begins charging, at which time it will begin displaying the actual voltage of the cell.
If you still have your instruction sheet I think this feature is probably better explained there. If you don't have a manual, it is available online or let me know and I'll PM you a link.