My new Energizer charger for NiMH 2500mAh AA batteries, does a full charge in about eight hours. I thought this relatively slow charge rate would be easier on the batteries....more so than some of the really quick chargers available. After charging a few hours, the battery temp reaches 57C. That seems pretty hot to me.
Anybody have any information on this subject? I'm not interested in quick charging, but rather a charger that will give the longest battery life.
Charging NiMH camera batteries..
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Arrgh! I just spent a long time trying to find this forum where I read and learned a ton about NiMH batteries and charging them, but I can't remember which one it was! Anyway, it was some digital camera forum, since people as fanatical about their cameras as they were, were equally as fanatical about battery performance and longevity. Seriously. People were comparing brands/models, tracking lifespan, keeping records of individual batteries, etc. 
Try this one, which has a Batteries forum:
http://www.dcresource.com/forums/index.php Archives are at the lower right corner.
This was a few years ago mind you, but what I read at the time convinced me that slow (trickle) charging was better. Based on their recommendations I went out and snatched up an (extinct) Radio Shack charger that automatically discharged and charged them, then kept them topped off. It takes all night, but that's why I have 2 sets of batteries.
Try this one, which has a Batteries forum:http://www.dcresource.com/forums/index.php Archives are at the lower right corner.
This was a few years ago mind you, but what I read at the time convinced me that slow (trickle) charging was better. Based on their recommendations I went out and snatched up an (extinct) Radio Shack charger that automatically discharged and charged them, then kept them topped off. It takes all night, but that's why I have 2 sets of batteries.
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Bluefront
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I've been researching various chargers......the best have "smart circuitry". My energizer model apparently uses a timer, and stops charging after a time based on the battery capacity. The better chargers are smarter.....they adjust their charge rate based on the battery voltage, and some measure temperatures, and adjust accordingly. Some provide different charge rates for each battery, and some give digital read-outs for the batteries.
I'm still checking this whole subject out......many different chargers are available.
I'm still checking this whole subject out......many different chargers are available.
That would depend entirely on the charging current. You also can't just run 200mA for 14 hours and expect a 2800mAh battery to be perfectly charged. IIRC the internal resistance of a battery rises when it's nearly full, and that's when it gets hot and the charger normally switches to trickle charging.
There is no way for a charger top "see" the capacity of a the battery being charged, unless it runs some kind of test run by completely discharging it and then testing how much it can be charged. A timer based charger would be too stupid to do anything like that.
Chargers meant for NiCd are also different from NiMh chargers, they have different charge patterns. Some have swithes to select the type of battery being used, and some are only designed to work with one type of battery.
There is no way for a charger top "see" the capacity of a the battery being charged, unless it runs some kind of test run by completely discharging it and then testing how much it can be charged. A timer based charger would be too stupid to do anything like that.
Chargers meant for NiCd are also different from NiMh chargers, they have different charge patterns. Some have swithes to select the type of battery being used, and some are only designed to work with one type of battery.
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Bluefront
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FWIW....documentation on these various chargers is conflicting/hard to find. My energizer charger states on the package that it will not overcharge, and you can leave it plugged in to maintain a charge. That doesn't sound like a pure timer operation at all......but some sites list this thing as "timer-based" operation. 
You are right about that... I have a pretty cheap Lenmar charger, and it says that for AA size batteries it uses a charge current of 260-320mA or a maximum of 0.896VA. NiCd charge time is 3 hours and NiMh is 8 hours. This information does not exist on the manufacturers site however... Newegg seems to have the pro99 for 14.99 with four 2300mAh batteries. I have no idea exactly how it charges, but so far it has worked just fine.
My experiences...
I've been racing for years with electric RC cars. I've used a lot of NiMh's. And also fried some, due to bad handling... boom !
There's a lot of hype and woodoo, when the talk is about NiMh's.
For some applications, slow charging is nice. But try that on a RC car, and your car will be very slow. Both in acceleration (instant high power drain) and top speed.
Now, for RC cars, we take it to the extreme. We find a HIGH temperature when charge is finished, is a good thing - because it lowers the internal resistance, which is very important to get that instant high power drain. The trade off is battery life span. If we get 40-50 good charge from a 60$ pack, we're happy.
This is of course another situation, than batteries for digi-cams.
However, there's an important similiarity to digi cams: instant high power drain. Of course, it aint even cloe to what a RC car draws, but it's still noticeably. Digicams do have instant high power drain, when shooting. Especially when the flash fires at full power.
Thus I'll recommend charging at a reasonably high charge rate. 1-2 hours seems to be appropiate.
If you choose to do that, it's important to get a charger with individual cut off and security circuits for each cell.
Reason: There's tolerances on NiMh cells. When they are new, they usually are quite even. But after some time, sometime only a few charges, one of the cells have less capasity than the others. So when charging all cells in series, one is fully charged before the others. And overcharge is bad. From here things tend to accelerate; Some cells in the pack wont be fully charges and one or more is overcharged. Same goes for discharging, one cell usually dump before the others, thus it gets over-discharged. That will reduce lifespan.
Another thing to consider, is that slow overcharging (often called trickle charge) result in increased internal resistance. So I'll strongly recommend not to leave the charger on more than an hour or so, after they are fully charged. This also apply for fast chargers, which usually switch to trickle charge, after the fast charge is finished. Some fast chargers automatically turn of trickle chargers after an hour or so.
Another good thing, is to discharge NiMh's from time to time, during normal use. Simply shoot with the camera till they dump. In general, NiMh like to be used, instead of stored.
For 2½ year, I've used a Vanson charger with individual cut-off and safety circuitry for my AA and AAA NiMh. I use Sanyo and Kodak batts. Next time I'll get new batts, I'll get GP, because they have lower internal resistance, than Sanyo.
But thing is, my AA's for digicams easily outperform my buddys, he's using a cheap and SLOW overnight charger. And with my 2½ years old Kodak NiMh's, I can easily capture 250 pictures with my Canon A80. Probably more.
To sum up a little, I'll recommend the following:
* Use your NiMh's frequently.
* From time to time (every 2-3 month or so), discharge them till the camera want new batts. That is, through normal use.
* Get quality batteries. Last longer, performs better.
* Get a quality charger, it'll save you money on batteries in the long run. Thus also more environmental friendly.
* Get a charger with a charging time of 1-2 hours AND individual cell cut off / security circuits.
* Preferable, get a charger which automatically shut off trickle charge after 1-2 hours. Alternatively, remember to stop the charge.
This Kodak K6100 seems to fit the bill - personally I mis control LED's for each cell, on the other hand, it's very compact and light, since the power adapter is built in.
http://www.kodak.com/eknec/PageQuerier. ... cale=en_US
http://www.kodak.com/eknec/documents/7b ... /K6100.pdf
Best regards,
Thomas
PS: One thing to remember. No matter how well you treat your batteries, they'll die at some point. However, treat them well, and they'll be good to you.
PPS: I also have a set of 8 Sanyo NiMh - they've lasted 6½ year by now. They still carry 80-90% of their initial capasity (I have equiepment to measure that). Not treated as well, as mentioned above. But always charged within an hour. So personally, I dont believe the charge-slow, live-long myth.
There's a lot of hype and woodoo, when the talk is about NiMh's.
For some applications, slow charging is nice. But try that on a RC car, and your car will be very slow. Both in acceleration (instant high power drain) and top speed.
Now, for RC cars, we take it to the extreme. We find a HIGH temperature when charge is finished, is a good thing - because it lowers the internal resistance, which is very important to get that instant high power drain. The trade off is battery life span. If we get 40-50 good charge from a 60$ pack, we're happy.
This is of course another situation, than batteries for digi-cams.
However, there's an important similiarity to digi cams: instant high power drain. Of course, it aint even cloe to what a RC car draws, but it's still noticeably. Digicams do have instant high power drain, when shooting. Especially when the flash fires at full power.
Thus I'll recommend charging at a reasonably high charge rate. 1-2 hours seems to be appropiate.
If you choose to do that, it's important to get a charger with individual cut off and security circuits for each cell.
Reason: There's tolerances on NiMh cells. When they are new, they usually are quite even. But after some time, sometime only a few charges, one of the cells have less capasity than the others. So when charging all cells in series, one is fully charged before the others. And overcharge is bad. From here things tend to accelerate; Some cells in the pack wont be fully charges and one or more is overcharged. Same goes for discharging, one cell usually dump before the others, thus it gets over-discharged. That will reduce lifespan.
Another thing to consider, is that slow overcharging (often called trickle charge) result in increased internal resistance. So I'll strongly recommend not to leave the charger on more than an hour or so, after they are fully charged. This also apply for fast chargers, which usually switch to trickle charge, after the fast charge is finished. Some fast chargers automatically turn of trickle chargers after an hour or so.
Another good thing, is to discharge NiMh's from time to time, during normal use. Simply shoot with the camera till they dump. In general, NiMh like to be used, instead of stored.
For 2½ year, I've used a Vanson charger with individual cut-off and safety circuitry for my AA and AAA NiMh. I use Sanyo and Kodak batts. Next time I'll get new batts, I'll get GP, because they have lower internal resistance, than Sanyo.
But thing is, my AA's for digicams easily outperform my buddys, he's using a cheap and SLOW overnight charger. And with my 2½ years old Kodak NiMh's, I can easily capture 250 pictures with my Canon A80. Probably more.
To sum up a little, I'll recommend the following:
* Use your NiMh's frequently.
* From time to time (every 2-3 month or so), discharge them till the camera want new batts. That is, through normal use.
* Get quality batteries. Last longer, performs better.
* Get a quality charger, it'll save you money on batteries in the long run. Thus also more environmental friendly.
* Get a charger with a charging time of 1-2 hours AND individual cell cut off / security circuits.
* Preferable, get a charger which automatically shut off trickle charge after 1-2 hours. Alternatively, remember to stop the charge.
This Kodak K6100 seems to fit the bill - personally I mis control LED's for each cell, on the other hand, it's very compact and light, since the power adapter is built in.
http://www.kodak.com/eknec/PageQuerier. ... cale=en_US
http://www.kodak.com/eknec/documents/7b ... /K6100.pdf
Best regards,
Thomas
PS: One thing to remember. No matter how well you treat your batteries, they'll die at some point. However, treat them well, and they'll be good to you.
PPS: I also have a set of 8 Sanyo NiMh - they've lasted 6½ year by now. They still carry 80-90% of their initial capasity (I have equiepment to measure that). Not treated as well, as mentioned above. But always charged within an hour. So personally, I dont believe the charge-slow, live-long myth.
Last edited by Thomas on Wed Jan 31, 2007 5:22 am, edited 5 times in total.
If you can dig up the manual, you might be lucky to find what you're looking for.Bluefront wrote:FWIW....documentation on these various chargers is conflicting/hard to find. My energizer charger states on the package that it will not overcharge, and you can leave it plugged in to maintain a charge. That doesn't sound like a pure timer operation at all......but some sites list this thing as "timer-based" operation.
Thomas
I never raced in the modified classes, just stock. So i only bought used packs from the "pros" who dumped them after ten charges. I have nott raced for several years though, and when is started 1700mAh Sanyo cells were the best available 
Some racers have different packs for training and racing, that way you wont kill your more expensive racing packs that fast and you can charge the training packs a bit slower to get some more life out of them.
I think i usually charged at 6A, it's been a while.
Anyway, even RC cars are slowly moving towards lithium batteries.
Some racers have different packs for training and racing, that way you wont kill your more expensive racing packs that fast and you can charge the training packs a bit slower to get some more life out of them.
I think i usually charged at 6A, it's been a while.
Anyway, even RC cars are slowly moving towards lithium batteries.
Re: My experiences...
So, with something like an mp3 player that can run for 20 hours on a single AAA batery, that's what a slow charger would work really well for?Thomas wrote:For some applications, slow charging is nice. But try that on a RC car, and your car will be very slow. Both in acceleration (instant high power drain) and top speed.
Now, for RC cars, we take it to the extreme. We find a HIGH temperature when charge is finished, is a good thing - because it lowers the internal resistance, which is very important to get that instant high power drain.
...
However, there's an important similiarity to digi cams: instant high power drain. Of course, it aint even cloe to what a RC car draws, but it's still noticeably.
Has anyone heard of eneloop batteries? Anyone have any experience with them?
Re: My experiences...
The Maha C401FS looks to fit the bill. It offers both a 100-minute quick charge and 5-hour slow charge mode and states that it has 4 individual charging circuits so that it charges and tops off each battery individually.Thomas wrote:If you choose to do that, it's important to get a charger with individual cut off and security circuits for each cell.
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Ralf Hutter
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Re: My experiences...
FWIW, I've been using one of these for almost two years now and am extremely pleased with it. I go through AA and AAA batteries like crazy, and am still using my original sets of Powerex batteries that I got when I bought the charger.AZBrandon wrote: The Maha C401FS looks to fit the bill.
Re: My experiences...
A typical UPS also charges the batteries very slowly (about 4 hours or so to 90%, a few more to 100%) and discharges them quickly (70A is not uncommon for a large unit). The batteries are good for at least 3 years, which is about the average shelf life of those batteries anyways. Not bad considering that they stay at about 100% most of the time and operate at elevated temperatures due to the inverter.Thomas wrote:I've been racing for years with electric RC cars. I've used a lot of NiMh's. And also fried some, due to bad handling... boom !
There's a lot of hype and woodoo, when the talk is about NiMh's.
For some applications, slow charging is nice. But try that on a RC car, and your car will be very slow. Both in acceleration (instant high power drain) and top speed.
Now, for RC cars, we take it to the extreme. We find a HIGH temperature when charge is finished, is a good thing - because it lowers the internal resistance, which is very important to get that instant high power drain. The trade off is battery life span. If we get 40-50 good charge from a 60$ pack, we're happy.
This is of course another situation, than batteries for digi-cams.
However, there's an important similiarity to digi cams: instant high power drain. Of course, it aint even cloe to what a RC car draws, but it's still noticeably. Digicams do have instant high power drain, when shooting. Especially when the flash fires at full power.
I have a Maha and bought one for my sister in law also--great chargers.
from the Imaging Resource: http://www.imaging-resource.com/ACCS/C204W/C204WA.HTM
the Great Battery Shootout from IR also:
http://imaging-resource.com/ACCS/BATTS/BATTS.HTM
Basically, the Maha does a pretty quick 1hr charge, but then maintains a *very* small trickle charge to keep batteries fresh. I have the Powerex 2500 batteries, btw.
from the Imaging Resource: http://www.imaging-resource.com/ACCS/C204W/C204WA.HTM
the Great Battery Shootout from IR also:
http://imaging-resource.com/ACCS/BATTS/BATTS.HTM
Basically, the Maha does a pretty quick 1hr charge, but then maintains a *very* small trickle charge to keep batteries fresh. I have the Powerex 2500 batteries, btw.