NiCad battery memory?

[Jim Weisgram]

[...snip...] I'd always heard that with NiCad batteries, you

[....snip...]

Just forget about the NiCAD, uh, something or the other.

[Phillip Hallam-Baker]

Good point, when Black and Decker first appeared they made a fortune by sticking cheap universal motors in their tools that were good for a couple of hundred hourse use. If you think of the amount of time that a drill is actually in use it is normally less than a fe3w minutes a day. contractors who spend their time fitting decks and the like tend to use the tools that are way up market.

When I did electronic engineering we had a lab experiment that involved measuring magnetic remenance curves. There is a battery 'memory' effect, over time the batteries really do loose their ability to recharge.

The remenance curves are different for different materials which is one reason why Lithium Ion is better than NiCad. But that is a 'soft' problem, you can cure it by simply draining the battery completely. The bigger problem with nicads is that they don't hold a lot of charge to start with and they tend to wear out after a relatively short number of charge cycles compared to LiIon. The battery manufacturers have done a lot to address these problems over the years and NiCads are much better than they were, but there is still a memory effect and they do still wear out over time.

I don't quite see how a battery cell could reverse its voltage. The voltage is the consequence of the difference in the electrode potentials. To reverse voltage the materials of the anode and cathode would have to change their atomic structure...

I really really would discourage folk from using anything other than a proper battery charger, particularly with Li-Ion. In the early days of developing Lithium ion batteries the labs used to regularly blow up. If you go by the old BBN buildings in cambridge Ma you can see a corner of one building in a different brick where they fixed the damage from a Li-Ion explosion. The energy density of Li-Ion is pretty high, in fact its higher than some explosives so messing about is a really bad idea. 'shocking a battery' with high voltage might not cause the battery to explode but they have been known to catch fire, see the tales of Mac laptops passim...

[Rolling Thunder]

snip:

Here's a web site that appears to be knowledgeable on the subject:

[Michael Houghton]

Howyd!

In article , Phillip Hallam-Baker wrote: [snip]

The cells won't be absolutely identical, and one will likely run down just a bit faster than the others (especially with time). As you run the battery down, that weak cell will go absolutely flat first, and then be driven by the remaining cells in the wrong polarity. That is, it will start charging from the other cells, but with its polarity reversed. That's especially bad for the battery.

Well, yep, that would be good advice.

yours, Michael