Appropriate Charge Rate for NiCad Batteries

The question is similar to the other thread about NiMH cells. What's the "recommended" charge rate of NiCad batteries?

NiCads are more robust than NiMH as they tolerate overcharging better and they can be discharged at a much higher rate. The big disadvantage of them is lower capacity and that they had toxic cadmium, but I have a few left and I want to use them in some in-house flashlights where the mAh is not an issue and you have plenty of spares near.

Since they produce a steeper drop at the same charge rates I think they can be charged a bit more gently than with the NiMH cells (I am thinking about smart chargers, not timed ones). What do you think?

And another question... NiMH can be damaged by overdischarge. How about NiCads? I saw in several threads the recommendation of deep-discharging and even store them short-cutted. Are this ok?

Yes, there is much discussion about charge rates.

Here's Battery University's Do and dont page, for a general guidline.

There isn't one charge rate that's best. It depends largely on how the battery cells are used, and other factors. Generally, if you discharge them at a slow rate, you want to charge them at a slow rate. If you discharge your cells at a fast rate, you want to charge them at a fast rate.

As for your question about over discharging NiCds, you can't really over discharge an individual NiCd cell. It's best If you don't routinely discharge below 1.0 Volt though.

NiCd cells in series, while being much more tolerant than NiMH cells, can be damaged by over discharging the pack, as individual cells within the pack can become reverse charged. Again, NiCd's can tolerate a bit of this, but it's not a good idea.

Dave

Hello Vali,

The maximum general recommended charge rate for NiCd cells is 2C.

You basically have two rates that yield good performance. The 0.1C rate timed for 16 hours, and a 1C rate using -dV termination.

Charging at rates in between these two works well with new cells, but can result in a missed termination with aged cells. fortunately, the NiCd chemistry is robust enough to endure missed terminations with minimal damage.

NiCd cells can also withstand discharging to 0 volts by shorting them out after they have been discharged down to 1.0 volts, but this is usually used in industrial applications and not usually recommended for consumer applications. The thought is that you can balance the cells in a battery this way, however, I find that you can achieve better ballance through 0.1C overcharging after the main charge.

Tom

It seems then that the charge rates for NiMH and NiCd are just the same and you cant take advantage of the steeper slope at the end of the charge to be more "gentle" on the battery and thus getting a larger lifespan.

Thanks for the answer too about confirming that deep discharging NiCad cells here and there are not destroying the batteries as it will with NiMH. I was aware of the dangers of multicells and reverse charging them, but I was thinking in the posibility of draining a couple in a Quark AA2. Since the same head can be used with only one cell down to, at least 1.0 volts, then if you use two in series I will probably end having less than 0.5 V in every battery sometimes.

vali said:

Since the same head can be used with only one cell down to, at least 1.0 volts, then if you use two in series I will probably end having less than 0.5 V in every battery sometimes.

Click to expand...

No you will probably NOT. One cell will be at 1.0V, and the other at 0.0V - you can put you house on it. Why? Because no two cells are a perfect capacity match.