Charge Rates ALL Battery Types

[LittleBill]

I've been reading for the better part of 3 hours about charging.

have a bc-900 exclusively eneloops.

i was charging at 200ma. started noticing high ma after being full 2.54,2.45a on a 2000ma AA

i believe the standard is .5c/1c so i am now running 1000/500 on AA, 500/250 on AAA

I also charge RC LIPO 1.8a 11.1v at 1.8a. these battery seem to be fine and are abused. i typically put back over 1500ma after a flight (7 minutes). i run full throttle whole flight. Thus they are charged at 1C. they have over 30-40 charges vs my eneloops less then 10 on all sets.

i also was reading about trolling motor batterys. a guy who was charging at 6 amps was killing a set of batts around 230A/H about every year. i charge my set at 2 amp and take over 48 hours to charge at only 30% power usage.

He switched to charging at 70+amps and his batterys are now lasting 3+ years.


my dad uses a 15 minute setup. has 0 problems and has been using them for years prolly 50 + cycles.

also my electric shaver charges 2 unknown AA in 31 minutes, obviously a hot charger. it still holds a 30 minute charge after 9 years..... it only had a 45 minute charge when new....

THE QUESTION

When did charging fast become a good thing. Is slow charging simply a thing of past since computer controlled charger didn't exist to cut the charge?


I've read the posts on missed terminations.

WHAT is everyone's experience??? it seems i am doing better with the fast charges at least in the LIPO world. I will charge them 6 times in 8 hours. with 0 time for cool down. i expected to replace them in a year. didn't happen.

 

[SilverFox]

Hello LittleBill,

The standard charge for NiMh and NiCd cells is 16 hours charging at 0.1C. Normal charging is in the 0.5C - 1.0C range when -dV termination is used. If your charger uses a different method of ending the charge, you can charge at different rates.

When charging at medium-low rates, the charger will often miss the end of charge signal, and the charge rate is high enough that the cell can't absorb the overcharge. This leads to damage to the cell.

The general rule of thumb is that if the charge rate is 0.1C or less, you can use a timed charger and the cell will usually be able to absorb the overcharge. The problem occurs when you charge in the 0.2C- 0.4C range. You can get lucky some of the time, but eventually as the cell ages the charger will miss the termination and overcharge the cell, doing some damage in the process.

With the advent of high capacity cells, it is hard to find an economic charger that is capable of charging at 0.5C, so many people struggle along at lower rates and hope that the secondary charge termination method will kick in before the cells is completely destroyed.

The charge rate is important in actual use under high drain conditions. This isn't actually the most important aspect of charging. The most important aspect in charging is termination. It just happens that the strongest termination signal with NiMh cells occurs when charging at the 0.5C - 1.0C rate, and this signal remains strong over the life of the cell.

Tom