Clarification of Charging and Discharging Rates

[mostro]

I recently purchased the MH-C9000 and have some noob questions about charge and discharge rates. I've read some of the threads on this but I think I'm more confused now than ever. :duh2:

I have several new sets of Eneloop AA's to form as well as some older cells which I would like to recondition.

One recommended sets of parameters I've seen entails using a long, slow regimen of .1C/.2C for charge/discharge. One the other hand, I've also read that many manufacturers are recommending values of .5C - 1.0C for these operations.

Is this determined by the method of charging? Some sources state that when using a charger employing negative delta voltage termination (not that I fully understand this term) as opposed to a timed charge there is some risk in overcharging the cell at .1C because the charger may miss its cue. Is there a consensus on this? Should these values be altered for Eneloops as opposed to the non-LSD cells I have lying around?

I imagine that the .1C/.2C that the MH-C9000 uses for Break-In mode is not necessary for day-to-day charging?

I realize that there may not be any black and white answers here, but I'm hoping for one or two simple formulas I can commit to memory to best prolong the life of the cells.

Thanks for the assistance!

 

[SilverFox]

Hello Mostro,

Welcome to CPF.

With most new cells I would suggest discharging them at the default 0.5 amps, then using the Break-In function. When that has finished, you can try to charge in the 0.5 - 1.0C range. This is also the way to try to revive older cells.

The Eneloop and other low self discharge cells seem to be already broken in, so you can either just use them, or do a discharge at 0.5 amps followed by a charge at 1.0 amps.

Every 20 cycles or so, or twice a year, discharge your cells at 0.5 amps and run another Break-In cycle.

If you plan to store normal NiMh cells, first do a discharge at 1.0 amps, then store them in a cool place. You can keep them in good condition by doing a charge/discharge cycle every 30 - 60 days. If you are storing them longer, at the end of the discharge, charge them at 1 amp for about 15 minutes, then put them into storage. When you are ready to put them into service, charge them up and use them.

You can use the default 1 amp charging with cells up to around 2400 mAh of capacity. Higher capacity cells will prefer charging at a minimum 1.5 amps.

It is possible to use lower charge rates with the C-9000, but you run the risk of overcharging your cells because of a missed end of charge termination.

Tom

 

[mostro]

Thanks Tom for the welcome and your considered response. I'll use those settings. I just spotted the 15 minute charger thread in which you've commented... obviously charging at these faster rates is about speed/convenience over longevity. Sometimes you need the juice fast, right?

Is the Wizard capable of anything approaching that kind of high speed charge (I'm guessing no), but if so what settings would you use?

Thx again,
Derick

 

[SilverFox]

Hello Derick,

2 amps is as high a charge rate as you can go with the C-9000. The charger tends to heat up when charging 4 cells at 2 amps, so I usually try to drop the charge rate down to 1.5 - 1.8 amps. This gives you cells charged in around 80 minutes. 15 minutes is a lot faster...

Tom

 

[phenwick]

Tom, thanks for the information. I printed it out to keep by my charger. I think it would be great to have a comprehensive tutorial to print out on proper charging and care of all types of batteries; NiCads, Nimh and Enloops. Is there a thread or do you have a write up of your knowledge and research?
It would sure make a great sticky for all the people who drop by here for advice.

 

[SilverFox]

Hello Phenwick,

Welcome to CPF.

One of the most comprehensive documents on battery care can be found at www.batteryuniversity.com

Tom

 

[phenwick]

Thanks Tom. I had this in my bookmarks and completely forgot about it.