NiMH Battery Question -- do they get hot when charging??

I just acquired a used digital camera from a CPF'er, that included a set of NiMH AA batts and a charger. Well the batteries he sent won't hold a charge, so I went to Wal-Mart and bought a set of Energizer 2100 mah NiMH rechargeables (4 for $9.83 - great deal!). I put them in the charger that was sent by the CPF'er (a Panasonic 6-hour model) and when I checked them 6 hours later they were quite hot to the touch. They seem fully charged, but I didn't apply an extended runtime yet.

Is it normal for NiMH batteries to get hot when charging? Might this be a problem in the charger? Might this be why the supplied batts (no-name 1800 mah) didn't charge?

This is my first exposure to rechargeable NiMH AA's, so all ideas are appreciated.

Thanks,

Dave

Yes, it is quite normal for the type of charger you have (one that charges in less than say 12 hours. The temperature rises quite rapidly as the charge nears 100%, if the rate of charge is high enough. In fact some chargers use a ten or fifteen degree C rise to 'detect' end of charge.

I don't know your charger, but I suspect it depends on a small but predictable *drop* in cell voltage about that same time. Anything that interferes with this (poor contact, abuse of the cell, etc.) fouls this up.

The 'fall back certain' charger is cheap but slow. It's the 'trickle' charger, typically taking up to a day. Perhaps a 'ride or two' on one might breathe new life in your 1800s? The cells are really quite robust (unless you overheat them, severely overcharge or reverse charge them). And most all the CPF folks seem quite up front to me, I wouldn't throw them out.......

Doug Owen

it is normal for any batteries to get warm when you charge them. The NIMH that I gave you is still good. I just use them for about 3 times. if you dont us them, can you send it back to me. I hate for you to throw away.

Thanks guys. I'll try cycling the ones that came with the camera again. When I charged them fully, and then put them in, they only ran the camera for about 5 minutes. How does one "wake them up" other than running through charge / discharge cycles?

Dave

How long do the 2100s run the camera?

2100s should run a typical digicam for at least 200+ shots...

Batts in "fast" chargers get quite hot, as hot, if not hotter, than body temp. And in the Rayovac pressure cooker (PS4), it can get downright explosive...

My 2 hour charger gets the cells pretty hot while charging.

Anytime you feed a AA battery more than 400mah, it'll get hot... There's no way around it, unless you stick it in a fridge. And even then, it'll still get hot... It's a resistor, alright...

[ QUOTE ]
FalconFX said:
Anytime you feed a AA battery more than 400mah, it'll get hot... There's no way around it, unless you stick it in a fridge. And even then, it'll still get hot... It's a resistor, alright...

[/ QUOTE ]
Here's my conclusion-after charging thousands of NimH cycles....

My much used CCrane unit (pulse) charges a single AA NimH @ 700mA. This causes the cell to sometimes get very warm, but not too hot to hold in a closed fist.

IMO-if you can't wrap your fingers around the cell and hold it without discomfort-...you are definitely hurting (at the very least), the actual capacity of the cell.

p.s.-I've got a half dozen NimHs that I have overheated with other chargers, and I'll gladly sell THOSE batteries to anybody--dirt cheap. /ubbthreads/images/graemlins/icon15.gif

I have been thinking of getting the CCrane Quick Charger to replace my cheap one from Radioshack, which gets the batteries quite hot. Is the CCrane charger really worth it?

[ QUOTE ]
Pi_is_blue said:
I have been thinking of getting the CCrane Quick Charger to replace my cheap one from Radioshack, which gets the batteries quite hot. Is the CCrane charger really worth it?

[/ QUOTE ]
IMO, in the $35. range-I sure think it is. /ubbthreads/images/graemlins/thumbsup.gif

What charger are we talking about? Any of the slow chargers I ahve used don't get the batteries hot. The 401 on the 5 hour setting only gets the batteries warm. I am asking because I have a guess this is a timer charger and might not fully charge 2100mA's. And might over charge smaller cells, hard to say without knowing the charger.

I'm guessing we're all taking about "fast" chargers, in the 1-2 hour range to charge up a 2000+mah AA cell... So something like a 700+ma current charger...

[ QUOTE ]
Brock said:
What charger are we talking about? Any of the slow chargers I ahve used don't get the batteries hot. The 401 on the 5 hour setting only gets the batteries warm. I am asking because I have a guess this is a timer charger and might not fully charge 2100mA's. And might over charge smaller cells, hard to say without knowing the charger.

[/ QUOTE ]
Is that "401" the Maha? -if you were asking me. /ubbthreads/images/graemlins/grin.gif
Not having any experience with Maha, I can't comment. BTW-how much does it sell for?

p.s.-the CCRanes I use all the time a DO nicely and Completely charge up my 1800 NiMh cells although taking about 15-20 min. longer to charge than my older NiMh AA 1200s-without getting the cells too hot to hold in a closed fist. (right out of the charger).

There are no doubt more advanced units available, but I haven't noticed any in the $35-40 price range.

The Maha C401FS is in the $35-$40 range from Thomas Distributing...

From 100-120min to 5 hours of charging and 4 separate channels, it's quite possibly the best NiMH AA/AAA charger out there right now...

Thanks, if I didn't have a lot of "C" and "D" cells to charge, I'd be lookin' at that one for sure.

Re: NiMH Battery Question -- do they get hot when

I think when Membr123 says the amperage of the ccrane charger is 700ma with a single aa battery he means just that; the unit is charging a single battery instead of 4 batteries..since the ccrane charges up to 4 batteries in parallel the average amps 1 battery out of the 4 batteries would see would be 175 ma.. so the batteries stay cool.
I haven't measured the actual amps the ccrane puts through various types of batteries though, does it always put out the same amperage?

I just posted a preliminary review of the Lenmar Mach 1 Gamma charger if you are interested. No more hot batteries

http://www.candlepowerforums.com/ubbthreads/showflat.php?Cat=&Board=UBB6&Number=296963&Forum=All_Forums&Words=&Match=Entire%20Phrase&Searchpage=0&Limit=100&Old=1day&Main=296963&Search=true#Post296963

Re: NiMH Battery Question -- do they get hot when

[ QUOTE ]
TedtheLed said:
I think when Membr123 says the amperage of the ccrane charger is 700ma with a single aa battery he means just that; the unit is charging a single battery instead of 4 batteries..since the ccrane charges up to 4 batteries in parallel the average amps 1 battery out of the 4 batteries would see would be 175 ma.. so the batteries stay cool.
I haven't measured the actual amps the ccrane puts through various types of batteries though, does it always put out the same amperage?

[/ QUOTE ]
Right you are, Ted-according to the charge time tables in the manual, the parallel circuit requires twice th time for twice the # of cells.

Example: 1300mAh AAs (1 cell)=42 min.
(2 cells)=84 min. etc. (4 cells)=168 min.---doing my sums.... /ubbthreads/images/graemlins/grin.gif 2h.48m.

It has three things going for it: simple to use, easy on the cells, and very reliable.

Re: NiMH Battery Question -- do they get hot when

The Maha 401 is a smart charger in both fast and slow modes. In my experience, even charging in fast mode, the 401 charges cooler than any other charger I have used including the 204 and it is charging at twice the rate (1000mA vs 500mA). They claim that it is due to their "unique FLEX NEGATIVE PULSE algorithm."

Someone has said it before but worth the repeat, " A good charger is more important than the battery." Without it you won't get maximum benefit from your cells and you'll cut their life drastically. What you'll save on a cheap charger will be far outspent with what you'll waste on prematurely ruined cells.

I'm sure that there are some other good chargers out there, but I don't know for sure about them. I do know about the 401 and highly recommend it. In addition, it comes with an unheard of lifetime warranty.