MH-C9000 Charger Missed termination

[shobhitk]

Hi all,
I am very happy with my MH-C9000 Charger. a small query though. I have 4 almost new (6-7 times charged) GP 2700 mah batteries which i wanted to charge in my mh-c9000 charger. 2 of them went niceley in the R&A mode and the charger terminated them with perfect precision. however the remaning 2 did not terminate at the correct time and when i checked them they showed a charging capacity of around 3940 mah with around 512 minutes elapsed in their final and last charging operation. also, i had seen silverfox say that the new mh-c9000 chargers can terminate perfectly even at 200 ma of charging current.
so am a bit confused as to why did this happen when i use all 4 of them simultaneously in my camera and for nothing else...they all should have behaved similarly...
any help would be appreciated.

PS: settings for all 4 of the batteries in R&A mode-
charging current - 400 ma
discharging current - 600 ma

Thanks

 

[Mr Happy]

I don't think Silverfox has ever said the C9000 can terminate perfectly at 200 mA of charging current; however I have suggested it myself when referring to some batteries such as eneloops. The reason for this is that the C9000 will terminate on a max voltage of 1.47 V and eneloops usually reach this voltage towards the end of charging. I am not familiar with the GP2700's so I do not know if they will reliably reach this voltage in the same way.

The important thing to note here is that you have not followed the charging guidelines in the C9000 instructions. The instructions recommend you to use a charging current of 0.3C or greater. In the case of a 2700 mAh cell this means you should charge at no less than 900 mA. It would be preferable to use at least 0.5C, which would be 1400 mA. When compared to these numbers your charging current of 400 mA was much too low.

 

[MarioJP]

When charging batteries, just in case the charger does miss termination. Since Most of these chargers have a LCD reading of how much current is being put into the batteries do you stop it exactly at the rated capacity or is there some overhead going on?

Also how far is too much to be considered a overcharged battery?

 

[Niconical]

GP chargers, a good and interesting range, especially for the regular but non-savvy user.

GP Recyko AA/AAA, very good, next best thing to eneloops IMO.

GP regular nimh 2700 on the other hand....., not so good. I have some of them which were included with my GP chargers, but it didn't take me long to realise that they're not too good, even by non-LSD standards. I got erratic results with them on my Mahas, including wild variations in capacity even from the same original sets.

 

[shobhitk]

hi all,
thanks for the views...hi Mr Happy, good to c u in the thread. mr happy i had seen silverfox's comment on this thread - http://www.candlepowerforums.com/vb/showpost.php?p=2776671&postcount=35

and yes i have not followed the instructions of the charger's manual. but i did this because after reading the manual and this forum and many other places the final picture which appeared was that we get maximum capacity, along with a prolonged healthy life of the cell only when charging at low charge rates...such as 200ma-500ma(approx.) it has been many-a-times reiterated that charging at higher rates does not charge a battery "fully" and as it produces a lot of heat, it finally results in reduced capacity of the cell thereby reducing its useful life substantially.
and as i am not in a hurry so i was trying to charge it at lower rates so as to get maximum charge out of it.

so what should be the correct method in this case...for fuller charge with proper termination?

also is there a way to set a timer by myself so as to terminate it after X no. of minutes?

thnx

 

[Mr Happy]

Thanks for the link. I did not remember that comment.

In general, there are two ways to charge NiMH cells: a low rate of 0.1C on a timer, or a high rate of 0.5C - 1.0C using a smart termination algorithm. There is not, in general, a middle rate.

The 0.1C method works because NiMH cells are designed so that they can be overcharged at 0.1C without being damaged. This means you can put a very full charge into them without needing to stop at exactly the right time. The 0.1C charge is what the break-in cycle on the C9000 uses.

The 0.5C to 1.0C method works by sensing changes in the battery voltage and temperature when charging is complete. These changes are easier to detect when the charging rate is higher. You will see plenty of consumer chargers out there that use a lower rate than this, but the good ones have very carefully designed microprocessor control to give reliable detection, and the poor ones can miss termination and damage batteries.

If you want a really full charge on an NiMH cell, safely and quickly, the best algorithm is to use a charging rate of about 1.0C with a very sensitive cut-off so the battery doesn't get warm, and then follow this with a 0.1C top-off charge for another hour or two. The C9000 approximates this by using a 100 mA top-off charge instead of a 0.1C top-off charge.

I forgot to mention about the GP2700 cells. I don't know anything specific about these, but it is possible they are not "good" cells like eneloops are. Therefore you need to be more strict about following recommended charging protocols.

 

[shobhitk]

thanks for the elaborate suggestion. i would definetly give it a try. also is there a way to approximately calculate the remaining time for the completion of a charging cycle when we know the value of the cell mah and the charging current?

 

[Mr Happy]

thanks for the elaborate suggestion. i would definetly give it a try. also is there a way to approximately calculate the remaining time for the completion of a charging cycle when we know the value of the cell mah and the charging current?

Yes. In general you can assume charging is complete when the charge supplied is equal to 110% of the capacity. So if you were charging at a 1.0C rate you would stop charging after 66 minutes. At 0.5C you would stop charging after 2 hr 12 min. On the C9000 you can look at the voltage and stop charging when the voltage is no longer rising. You can also feel the temperature of the cells and stop charging when they seem to be getting warm.

 

[TakeTheActive]

...is there a way to approximately calculate the remaining time for the completion of a charging cycle when we know the value of the cell mah and the charging current?

...In general you can assume charging is complete when the charge supplied is equal to 110% of the capacity. So if you were charging at a 1.0C rate you would stop charging after 66 minutes. At 0.5C you would stop charging after 2 hr 12 min...

Based on my reading of the CPF 'Batteries Included' Archives, Charge EFFICIENCY is not LINEAR (1.0C @ 66min, 0.5C @ 132min), but is based upon Charge Current - i.e. Charging @ 1.0C is more efficient (requires ~120% input) than 0.1C (requires ~160% input).

Reference(s):

• Theory: Nickel-Based Rechargeables
• Theory: Optimal Charge Rate: new technique to find

...On the C9000 you can look at the voltage and stop charging when the voltage is no longer rising...

IMO, this answer is incomplete - referring to "-dV/dt" - it should say '...stop charging when the voltage is no longer rising AFTER xx minutes'. i.e. How long should shobhitk wait / observe the voltage before deciding that it hasn't changed?

...You can also feel the temperature of the cells and stop charging when they seem to be getting warm.

Without using a thermometer, WARM is a relative term. IME, compared to room temperature, 100°F feels warm. But, from my CPF Archives reading, cells are perfectly safe up to ~120°F, which, IME, feels relatively HOT. :devil:

A phrase I heard recently on a TV drama show (Law & Order?) comes to mind - "Risk vs Reward". Paraphrasing, 'We can make it better, but then it would be so expensive that no one would buy it'. IMHO, the Maha MH-C9000 is a *GREAT* value for the money *IF* you follow the Maha manual (aka manaul ) *AND* the CPF 'Batteries Included' Gurus recommendations. This charger is 'Smart', BUT not foolproof! Lower the Charge Current, and thus lower the DeltaV, out of the charger's detectable range and be prepared to MISS proper termination.

The Maha MH-C9000 is *VERY* versatile. Sure, you can charge a 2700mAh AA cell @ 200ma (0.074C), or a 800mAh AAA cell @ 2000mA (2.5C). BUT, is that in YOUR best interest? :sigh:

Follow the RULES, correctly interpret the RESULTS and you'll be rewarded with ABOVE AVERAGE cell life. :thumbsup:

CLICK on my Sig Line LINK for many excellent, informative posts from the CPF 'Batteries Included' Archives.

 

[MarioJP]

I never had any problems of missed termination but then again i am the kind of person that likes to charge batteries at higher current rates:twothumbs. But 200ma charging rate, really wow lol. I do not own this charger but I am sure all nimh charger has to have a termination of some sort.

Any cell above 1000 should not have its charging rate 200ma that's just my opinion.

 

[TorchBoy]

Re: MH-C9000 charger missed termination

I am very happy with my MH-C9000 Charger.

What's the model number on the back of your charger?

 

[shobhitk]

taketheactive thanks for an indepth analysis...i'll try to follow the rules and reap the fruits