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Old 03-06-2006, 09:27 AM   #1
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Default The Truth About NiCd Batteries

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Title: The Truth About NiCd Batteries
URL: http://www.hardwaresecrets.com/article/292

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"Nickel-Cadmium (NiCd) is a very well known rechargeable battery technology, used by several electronic equipments, such as laptop computers, cell phones, cordless phones, old motherboards, etc. It is ..."

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Old 12-22-2009, 11:19 PM   #2
Olle P
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Digging up this old article, since I just now found it...

Page 1:
Explanation of the memory effect.
I've always thought of it in the opposite way: The battery think it's empty when it isn't.
After all, when you charge it fully it will reach the full voltage.

Page 2:
There's no explanation to why these crystals appear in the first place. Why don't they appear when the battery is fully cycled? Or do they?

I've read several articles on the subject of the memory effect. Some say it exist while others claim it doesn't.
After all, everybody agree that batteries do lose some capacity with each cycle (charge and discharge), no matter if the cycle is between empty and fully charged or only cover a small portion of the capacity.

My own theory is that the perceived memory effect is usually a matter of many cycles and/or overcharging rather than the specific habit of not having each cycle go all the way.

Monitoring current NiCd charge status is very hard, because NiCd batteries don’t present a linear discharge ramp. The voltage found on a NiCd cell stays at 1.2 V until the battery is “discharged”. So even if the battery has only 30% of its charge, it will keep providing 1.2 V on its output, for example. ...
Regular non-rechargeable 1.5 V present a linear discharge ramp, so when it has 50% of its charge, it will provide only 0.75 V on its output.
This isn't completely correct.
The discharge curve is pretty much the same with any type of battery.
A fully charged battery has a voltage somewhere above the nominal value. For NiCd and NiMH this is 1.4V per cell, alkaline batteries are about 1.7V.
As you start the discharge (using constant current) the voltage quickly drops to slightly above the nominal value, about 1.25V for NiCd, and then become as good as linear with a slight slope (it's this linear within the 90-10% of capacity range). When the battery is almost drained the voltage drop increase speed again.

It's also pretty easy to monitor the battery status, using modern electronics.
You just keep track of how much current that flows in and out of the battery while also adding the factor of internal discharge.

Page 3:
Much text to cover very little matter...
- You have a battery that's essentially dead.
- If you don't zap it, it will stay dead.
- If you do zap it, it might come back to life. Just don't expect too much from it...

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