AAA charging on MH-C9000: the lowdown

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Hoggy

Hoggy

Newly Enlightened
Joined
Jul 28, 2008
Messages
177
Location
WI, USA
Hey everybody,

I've heard some not-so-good things about AAA charging on the C9000. I'm primarily talking about the 2 hour 100ma top-off charge.
I've recently read some posts about this not being good for AAA's and I'm inclined to agree.

However, I didn't hear about this until about a month ago - and I bought my C9000 several months ago. I did many searches and eventually found a few posts saying that the top-off charge might not be so good for AAA's, but they didn't elaborate on it much and it was dismissed. And those posts seemed to be few and far between.

So.. What IS the deal with charging AAA's on the C9000?

Is it safe or not? Or is it safe, but with caveats??

(Please don't make this an anti-C9000 thread, as I will not give up my C9000 due to the other useful features(i.e. break-in).)
 
IMO too the 2 hours top-off at 100 mA may be a bit of an overkill with AAA cells. I think the optimal top-off conditions could have been set at 1hour at 100 mA for AAA and 1 hour at 200 mA for AA cells.
That said, it is unlikely that the limited overcharge that occurs during the top-off of AAA will have any significant effect on cycle life since the overcharge is at low current and is rather brief. If you are concerned about this, you can run the c9000 with a timer. Something like 2.5 hours at 500 mA should do.
 
Although the top off charge is stated as 100 mA, most currents on the C9000 are actually 90% of the stated value and I suspect this one is too, which would make it 90 mA. If so, 90 mA is pretty close to the 0.1C rate for most AAA cells and that would be perfectly safe to apply for two hours. It would cause no harm at all.

If you add to this that cells like eneloops will stop the main charge when only about 90-95% full, the top off charge is not even an overcharge. So I think there is no cause for concern.
 
I thought it was 0.1C for 1 hour followed by trickle charge value of around 10mA for a further hour.
 
My math on this is as follows:

Lets take fast charge at 0.5C on an Eneloop AAA cell with a true measured capacity around 800 mAh (most of them are).
Cutting at 1.47V on a healthy cell corresponds to approximately 90% charge, i.e. 720 mAh of usable discharge capacity.
This is followed by two hours top-off at 100 mA (could be 90 mA).At this state of charge and current, the charging efficiency is about 60%, so 2hx90mAx0.6=108 mA of usable capacity put into the cell. Now, add to this 720 and you'll end up with 828 mA of a total input capacity (considering charge efficiency) or 3.5% overcharge. At 0.11 C this is indeed unlikely to cause any significant reduction in cycle life.
 
So, how does one measure the top-off charge with a DMM?
I'm new to owning a DMM, so forgive me if I'm not 'getting' something..

Considering it's charging, does one put the positive lead on the negative tab and the negative lead on the positive tab?

Am I right in assuming that one could put the leads on the 'other' tabs? As in the AA tabs while charging AAA's.. They are connected, right?
(Just by looking, I can tell the positive tab is definitely connected.)
 
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you can not say, well its only 11% overcharge, and that is not a problem.
because HOW it gets that 11% makes the most ammount of difference.
(its in the book)

and that is what all the spec sheets read , overcharge within the safe overcharge causes very little damage, overcharge beyond those specs causes major damage.

you can, and i HAVE overcharged a enloop AA for HUNDREDS of hours, within spec, solely to prove that it was WITHIN its specs, i even took the overcharge very high too, you could not tell that enloop from the other enloops of the same age and cycles.
BUT
i have overcharged for mere hours Above spec (overcharge state), and it gassed out.

the 90 would be within spec like Mester happy said , for a GOOD AAA enloop, unless its a 1000ma charge, at 10% pulse cycle , which it isnt right?
and Unless the battery went into a full overcharged State, and then STAYED (was held by the 100ma) in that state, which that charger cant right? because everyone discovered it cuts off with high voltage.

sooo, surely you can see that, there on the machine? when the charger goes from it thinking its charged to topping off, does the voltage take a dive or maintain, or continue slowly up?
during the topping phase of charge , does the voltage take a dive maintain or continue up?

IMO there is NO AA charger that treats a AAA perfectally, they are so small and cute and the chargers are so Mean :)
and no AAA lives forever compared to the AAs, and reverse charge on them is pure heck for them. so i gave up on being able to keep them as long as the AAs.

oh wait, its all my opinion anyways :)

most of these ni-?? battery things are speced to be able to handle .1c or 10% of its capacity rate of charge, without causing it harm.
The really well built tank ones , like the old low cap, and these new LSDs of low-cap, can easily handle the 10% of its capacity charge for extended time. heck that IS how the 16hour .1c charge works, its what it depends on. the enloop AAs will handle lots more than that without faultering, when they are good and fresh and new, and will probably handle the .1c easily when older and weaker and not doing as well.
but
if its been put into an overcharged state by a fast charge or drop temination, or something, then continually assaulted IN that state, that wouldnt be good for them at all.
simply because its then been taken over the specs.
cause
none of these thing can handle being in an overcharged state, and still being charged

the rotten glossary:
Overcharge - battery is no longer accepting a charge , but your doing it anyway :)
overcharge specs - manufacture specs that indicate the quantity you can keep charging it when battery is no longer accepting a charge
Overcharged state - my word for it having reached high pressure , temperature threshold that is bad for it, visualised by drop in voltages
(that'll fix it)
 
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Hoggy said:
So, how does one measure the top-off charge with a DMM?
I'm new to owning a DMM, so forgive me if I'm not 'getting' something..

Considering it's charging, does one put the positive lead on the negative tab and the negative lead on the positive tab?
Click to expand...
OUCH!!!

When someone asks a question like this, the FIRST thing I think of is to tell them to STOP! :oops:

The next thing is to point them to READ *ANYTHING* regarding to basic electricity. PeAK, as an instructor, probably has some good LINKs.

Hoggy said:
...Am I right in assuming that one could put the leads on the 'other' tabs? As in the AA tabs while charging AAA's.. They are connected, right?
(Just by looking, I can tell the positive tab is definitely connected.)
Click to expand...
Well, just UNPLUG the MH-C9000 and measure the resistance between the AA and AAA negative tabs, eh? ;)

BTW, what are you trying to accomplish? :confused:

IF you want to read:
  • VOLTAGE: you'll connect PLUS to PLUS and MINUS to MINUS (parallel)
  • CURRENT: you'll connect PLUS to MINUS and MINUS to PLUS (series)
 
dang , i am gonna have to stop and read it now.

i never worry about which way i connect my DMM for voltage, its reads it foreward or backwards :D really .
cept that one with the bent needle (thats gotta hurt)
 
Hoggy said:
Am I right in assuming that one could put the leads on the 'other' tabs? As in the AA tabs while charging AAA's.. They are connected, right?
(Just by looking, I can tell the positive tab is definitely connected.)
Click to expand...

the other thing he is asking
is one side of the battery connection terminals all connected to a similar ground?
the AAA connecting terminals, VRSES the AA connecting terminals, are they a single piece of metal connection for either battery?

this is true for the similar models.
 
TTA - no need to yell..
I'm asking because I don't intend to go sticking the probes into anything willy-nilly. I want to hear of others doing the same thing before I, myself,do it.
While I admit that I could know more about electricity, I'm kinda at the limit of what I can read - and understand, without going further into the realm of actual testing. Only when I start to test things with my DMM, can I begin to truly comprehend the things I read about.

BTW, I did the resistance test with the C9000 off. It showed varying resistance measurements and usually ended near 0.. I'm not sure how to interpret that yet - except maybe that my measurements were being scewed by how hard I could press on the contacts.

But my goal within this thread's context, is to measure the amperage that the C9000 is putting to my batteries. I'm not confident enough to know how to do that yet - so my probes will NOT be touching the C9000 while on.
 
Hoggy said:
But my goal within this thread's context, is to measure the amperage that the C9000 is putting to my batteries.
Click to expand...
That is not something that is easy to do. It is best just to look at the clock when you start a charge and then watch the C9000 display. Compare the elapsed time on the clock with the time on the display and you will know how long since DONE appeared. Sometimes you can also see the displayed voltage creeping up.
 
Hoggy said:
But my goal within this thread's context, is to measure the amperage that the C9000 is putting to my batteries. I'm not confident enough to know how to do that yet - so my probes will NOT be touching the C9000 while on.
Click to expand...

you sure picked the easy one didnt ya :)

I find it difficult to do that with the usual equiptment, and here is why
those things are connected up with very little Resistance at all, very direct there.
any added resistance is going to throw everything off fast.

which woudnt be a problem if:
just the leads on a DMM are a huge ammount of resistance in a situation like this, because there is so little original resistance.

anything bumps around or is partly connected , and the poor computer cant do anything right :)

there is zero clearance or tolerance for connections between stuff.

the ammeter itself has enough resistance to throw everything off


so as you know you gotta get an ammeter in-between the 2 items
i do it something like this:
pictures :)

+|{=====]|- <- this is your battery in there

+|{=====]<-ammeter->|- <--stick meter between battery and charger. here

+|<-ammeter->{=====]|- <--- or here

if you make a very thin sandwitch , you can stuff it in between, sandwitch has metal, then insulator and metal and something to connect to on the 2 metals
|()|
then you go get some good copper speaker wire , and stuff some banana plugs on it, and solder them good, for connecting to the meter, and keep it short. and connect it onto both pieces of bread on the sandwitch. then you try and shove the sandwitch in there, with it OFF, and check everything so it isnt shorted.
 
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on the non-computer ones with a lot of clearance, you can jam the leads in between, and push the battery away from connecting keeping the leads connected to the 2 places, without connecting eachother. for a cheap quick test.

. . . . .. . .\ /
+|{=====]X|

chopstix
then you buy new leads, cause those are bent ;)
 
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Bones said:
Yes, as VidPro has stated, they are definitely connected Hoggy:

http://www.candlepowerforums.com ... post2810241
-
Click to expand...
A picture is worth a thousand words, eh?

mh-c9000-contact-tangs-marked.jpg


Thanks Bones :)
 
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