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Ni-Cad Battery "Memory"

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Old 07-22-2010, 03:40 PM
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tri-squire
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Default Ni-Cad Battery "Memory"

Is there an inexpensive means of "erasing the memory" of a Ni-Cad battery other than using an expensive battery conditioner ?
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Old 07-22-2010, 05:13 PM
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Default RE: Ni-Cad Battery

If a Nicad is losing significant capacity it might just be time to replace it. Nicad and NiMh batteries are relatively inexpensive these days and buying a new battery sure beats losing an airplane.

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Old 07-22-2010, 06:06 PM
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Default RE: Ni-Cad Battery

You can try cycling the battery in a discharger/peak charger type battery charger but they will never be like new. When you get tired of messing with it, buy a new one.
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Old 07-22-2010, 08:21 PM
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Default RE: Ni-Cad Battery

Here's the skinny from the battery guru C.L."Red" Scholefield's websight

2.9) Does the memory effect exist?
YES
Just as everyone is running around and saying that the memory effect is a myth, here I am, saying that it is true. OK, so, why is this? First of all, the term memory effect is quite unscientific. People tend to attribute any failure of a NiCd to memory.

Let us define memory as the phenomenon where the discharge voltage for a given load is lower than it should be. This can give the appearance of a lowered capacity, while in reality, it is more accurate to term it voltage depression.

Memory is also hard to reproduce, which makes it hard to study. Originally, memory effect was seen in spacecraft batteries subjected to a repeated discharge/charge cycle that was a fixed percentage of total capacity (due to the earth's shadow). After many cycles, when called upon to provide the full capacity, the battery failed to do so. Since we aren't in space, the above is not really relevant...

Let us look at various causes of "memory" or voltage depression.

Memory can be attributed to changes in the negative or cadmium plate. Recall that charging involves converting



Cd(0H) to Cd metal.
2

Ordinarily, and under moderate charging currents, the cadmium that is deposited is microcrystalline (i.e. very small crystals). Now, metallurgical thermodynamics states that grain boundaries (boundaries between the crystals) are high energy regions, and given time, the tendency of metals is for the grains to coalesce and form larger crystals. This is bad for the battery since it makes the cadmium harder to dissolve during high current discharge, and leads to high internal resistance and voltage depression.
The trick to avoiding memory is avoiding forming large crystal cadmium. Very slow charging is bad, as slow growth aids large crystal growth (recall growing rock candy). High temperatures are bad, since the nucleation and growth of crystals is exponentially driven by temperature. The problem is that given time, one will get growth of cadmium crystals, and thus, one needs to reform the material. Partial cycling of the cells means that the material deep with the plate never gets reformed. This leads to a growth of the crystals. By a proper execution of a discharge/charge cycle, one destroys the large crystal cadmium and replace it with a microcrystalline form best for discharge.

This does NOT mean that one needs to cycle one's battery each time it is used. This does more harm than good, and unless it is done on a per cell basis, one risks reversing the cells and that really kills them. Perhaps once in a while, use the pack until it is 90% discharged, or to a cell voltage of 1.0V under light load. Here, about 95% of the cells capacity is used, and for all intensive purposes, is discharged. At this point, recharge it properly, and that's it.

The more common "memory effect" isn't memory at all, but voltage depression caused by overcharging. Positive plate electrochemistry is very complicated, but overcharging changes the crystal structure of the nickelic hydroxide from beta-Nickelic Hydroxide to gamma-Nickelic hydroxide. The electrochemical potential of the gamma form is about 40 to 50 mV less than the beta form. This results in a lower discharge voltage. In a six cell (7.2v) pack, this means a loss of 300 mV. Trick? Don't overcharge. Leaving cells on a trickle charger encourages formation of gamma nickelic hydroxide. Expect the cells to discharge at a lower voltage.





2.10) Summary
DON'T deliberately discharge the batteries to avoid memory
DO let the cells discharge to 1.0V/cell on occasion through normal use.
DON'T leave the cells on trickle charge for long times, unless voltage depression can be tolerated.
DO protect the cells from high temperature both in charging and storage.
DON'T overcharge the cells. Use a good charging technique.
DO choose cells wisely. Sponge/foam plates will not tolerate high charge/discharge currents as well as sintered plate.
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Old 07-22-2010, 09:18 PM
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Default RE: Ni-Cad Battery

Getting to be time for the pop corn and coke
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Old 07-22-2010, 09:56 PM
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Default RE: Ni-Cad Battery

I spent $50 on my cycler used, and it can charge batteries that I don't even own yet. That's pretty inexpensive in my book, especially given the time it saves me with the fast charge feature and the money it saves me by letting me verify my batteries instead of tossing them when they reach a certain age.
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Old 07-22-2010, 10:30 PM
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Default RE: Ni-Cad Battery


ORIGINAL: w8ye

Getting to be time for the pop corn and coke
ba ha ha ha ha, yea it's a bit wordy, your advise is sound, just get new packs.

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