Recommended Charging Currents?

[Action]

I know this is probably covered somewhere, but I cannot find it.

Assuming that I am using a charger that permits the choosing of multiple charging rates, how do I calculate (as best as possible) the optimal charging rate by battery type? I am less concerned about speed and more concerned about battery life and capacity.

I am charging AAA, AA, C, & D NiMH batteries of various capacities.

I am also charging a very wide range of LiIon batteries from RCR123's, 17500, 17650, 18500, 18650, and the new AW 'C' sizes batteries.

Is there a quick guide somewhere for charging rates or a rule of thumb?

 

[SilverFox]

Hello Action,

The NiMh battery manufacturers recommend charging at a rate that allows the charge to be completed in 1 - 2 hours. This means that you set your charger to a 0.5C - 1.0C charging rate. If you have a battery with a capacity of 2400 mAh, a 0.5C charging rate would mean that you charge at 1.2 amps.

Li-Ion battery manufacturers have a variety of charge rates recommended. Most of them fall in the 0.5C - 1.0C range, using a CCCV algorithm. The maximum cell voltage should be 4.200 volts, and the charge is terminated when it drops to around 0.05C. If you have a 2400 mAh Li-Ion cell, a good charge rate would be 0.8C or 1.9 amps (or we can round hat up to 2.0 amps for convenience), and when the current drops to around 120 mA, the charge is complete.

Tom

 

[Action]

So generally do you charge at the high end or low end of the 0.5C to 1C levels?

So does this still apply to higher capacity cells such as 11000 mAh D NiMH and to AW's 'C' cells? 1C on these babies is pretty stout...

 

[SilverFox]

Hello Action,

It depends on what charger I am using. I usually try to get close to 1.0C for NiMh cells, but settle for 0.8C for Li-Ion. Li-Ion can handle slower charge rates, so it is not as important with them.

The high capacity C and D NiMh cells seem to charge fine at 2 amps, at least they do very well on the Maha C808M, but I strive for 0.5C on those cells as well. My Schulze charger is capable of 5.5 amps and that rate works very well on my high capacity C and D NiMh cells.

The Maha C9000 heats up when charging at 2 amps, so I do most of my charging with that charger at 1.5 amps.

With the BC-900 and charging 4 cells, I always use the 1 amp rate. With 2 cell charging I bump that up to 1.5 amps.

Li-Ion cells are supposed to have the charge terminated when the charge rate drops below around 0.05C. I think that as long as you are able to charge at a rate above that, you should not have any problems.

The problem with slow charging Li-Ion cells is a safety issue. You are supposed to attend to Li-Ion charging to make sure nothing gets out of hand. Most people are not able to attend to a 10 hour charge, so they end up leaving them unattended part of the time. If you charge outside on the patio, its no big deal, but if you charge in your house and something goes wrong, it can result in more severe ramifications.

Tom

 

[NA8]

Is there a quick guide somewhere for charging rates or a rule of thumb?

The tricky thing is there's the theoretical and then there's what you're provided with by the manufacturer of your battery charger. It's better to charge at low currents, but there's a technical problem getting a battery charger to sense end of charge and shut off without getting into false stops or missing the stop entirely. For better charger performance, the manufacturers seem to be leaning towards higher charging currents than the "low currents" one might prefer. Batteries are cheap, I'd go with the recommendations of the charger manufacturer and not worry about the theoretical lifespan of an endlessly cycled battery.

 

[sp5it]

Use this calculator.
http://www.csgnetwork.com/batterychgcalc.html
Mike

 

[MidnightDistortions]

Reviving this old thread but, i was curious on what is the minimum charge rate you should use on C and D cells? I know that 200-300mA is ideal for AAA cells and that 500-700mA for AA cells, what about C and D cells? People say it's best to charge at low currents but i find that charging at low currents isn't always necessary to do, especially if you have some charge still in the battery. Would 0.7A be enough for D cells or should you choose the 2A option instead for proper termination?

 

[SilverFox]

Hello MidnightDistortions,

Over the years I have found many data sheets that recommend 2 amp charging for C and D cells. I pretty much stick to that and have no termination issues. At 850 mA I have seen several missed terminations with C and D cells, so you should probably go higher than that.

Tom

 

[jasonck08]

Tom is right. I would say probably the industry average for "recommended" charge rate for 18650 (laptop grade cells) is about 0.5C. Sometimes I see as high as 0.7 or 0.8C. Generally you never want to charge a non-high drain Li-ion cell at above 1C, or discharge above 2C.

I would say though generally I see charge termination currents in the 50-75mA range for 18650 cells in most datasheets. Most hobby style chargers will do 5-10% of the programmed charge current for the termination current. So if you charge at 1A, you will get a 50-100mA termination. The lower the termination current, the more charged the battery will be. But you might get 1-2% more capacity out of the cell with a low termination current, but might lose a few charge/discharge cycles.

With powertool grade cells its a whole different ball game. Often times 1-2C charge currents are considered standard.

If you really want to prolong the cells life, get a charger that will terminate at 4.10v. Or just pull the cells off early. 4.1v charging you will have about 90% cell capacity but roughly double the cycle life, and less overall cell idle deterioration. (600-1000 cycles vs 300-500).

 

[MidnightDistortions]

Hello MidnightDistortions,

Over the years I have found many data sheets that recommend 2 amp charging for C and D cells. I pretty much stick to that and have no termination issues. At 850 mA I have seen several missed terminations with C and D cells, so you should probably go higher than that.

Tom

Oh thank you Tom! I had always figured the more capacity a battery has the higher the charging current should be.

Also i remember seeing somewhere that there's a D and maybe C adapter that you can put on the Maha C9000, that would be good to have to check capacities of a C or a D cell, i eventually plan on getting some NiMH D cells in the future. Something like this, http://www.amazon.com/Battery-Adapter-BT-C2000-BT-C2400-Chargers but the description isn't entirely sure if it'll work on the C9000. I just looked it up so i can always ask on the page.

Edit: Just bought a couple of those adapters (they seem to work according to the more recent reviews) and got some Sunlabz D batteries, so excited, it's ok for $30 but hoping it will work.