reman

Hi all,
I just got a 2500mAh battery to replace the 700mAh ni-cd in my futaba TX.
The sticker on the 2500mAh battery says to "charge it for 14/16 hours at 250mAh"
So does that mean that using the 70mAh charger the 2500 will take up to 57.15 hours to charge ?
What would the maximum "C" rating for ni-mh batteries ? (can you get fast chargers for the TX ?)

Also, I have a charger kicking about from an rc systems minicopter, It's 9v and 350mAh, would this kill the pack ? ( either by being .6v to low or 100mAh higher than recommended )

Motions

The wall wart charger is a trickle charger. If the battery is completely dead, then yes it would take quite some time to charge. Just use a regular Ni charger and charge at 2.5A.

Rodney

Yes, the 70 ma charger should charge it in the 57+ hours. That is not a trickle charge. By definition, trickle charge will vary with different brands and size of cells, and is that charge rate which will just overcome the self discharge rate of the battery. Charging at 0.1C (250 ma in your case) is properly defined as "Slow Charge", not trickle charge. Your battery will last longer and give better service when charged at the 0.1C rate although you can safely charge most NiMh's at 1C if you monitor temperature and never let the battery get hot, slightly warm at end of charge is okay. Even if you charge fast (the 1C rate) you need to occasionally do a slow charge to equalize the cells in your battery; reason, no group of cells comprising a battery will be exactly alike and will eventually become unbalanced or unequalized over time. An occasional slow charge will rebalance the battery.

Geistware

My Feedback: (16)

Lets define a trickle charge.
A trickle charge is a charge current of C/20 to C/50
At 70maH, this charger will be a trickle charge to a pack of 1400maH or larger.

The real question is if you can charge a pack with this level of current.
The answer is yes.

reman

So what does that mean then ? On a trickle charge can the battery be left charging when full for longer before any damage happens ? Can it be left at this rate for days at a time without a problem ? Does the old "if it feels warm its done" still apply or will it even get warm ? Its been charging now since Saturday night, By my estimate it should be finished by 6am Tuesday [] and then I have to discharge it fully again. To what voltage would Fully be ?

Rodney

Trickle charge is defined differently by different manufacturers, as Geistware said, usually at about C/20 or C/50 but not always. There is not a well defined definition and it varys from manufacturer to manufacturer. That is why, IMHO, it is always best to define any charging in terms of C, not by trickle or slow as that eliminates all possibility of missinterpretation by the newcomer to battery management. There is much ambiguity on proper battery care in all these forums, some downright wrong. Again, IMHO, there are very few reliable sources, some being Geistware, Norton and --very good--www.rcbatteryclinic.com.

reman

I had to do something about the TX charge time so I bit the bullet about a week ago and got a Multiplex LN-5014 charger.
Like lots of 'um these days it does everything I need and somethings I didn't know I needed, like when it cycles a pack it lets me know how much power it put out ( the original 700mAh pack only held 550 mAh on the first cycle, by the 4th it was up to 720 !!! ). The 2500 pack charged in 10 hours ( had three flights + a lot of testing on it so far and its still reading over 10 volts, with the old one the second flight always had to end early when the TX starts bleeping at me )

All I need now is a 3 cell balancer for for it and then I can use it on the lipo's to