nicad rechargeable battery

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snapper

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Nov 8, 2002
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This is a bit off topic so I hope no one mines. This pertains to a twelve volt battery pack for a drill. The way i understand nicads is when they are full they are 1.4 volts a cell and dead 1.2 volts a cell.. So since a 12 volt pack has 9 cells when fully charged it should read 12.6 volts.. When dead it should read 10.8.. So If i put a meter on the pack it should be between 12.6 and 10.8, right?? So if it is close to 10.8 volts it is proably time for a recharge right?? Then i read that when a pack is fast charged the cells have 1.55 volts in them and then slowly drops.. So when it just gets done charging it should read under 13.95 Right?? And to confuse me even more, can some one explain the memory phenomenon? Where a pack loses it ability to hold a charge for very long? And is there any way to reverse it?? I read that some times freezeing a pack will reverse the memory? I am trying it now on a pack so I will let ya know.. What is your opinion?

Thanks in advance for teaching me the basics of nicads..
Later snapper..
 
Nicd's can be upto 1.5v per cell, but that's rare to have a cell that "hot." After a recharge, most 1.2v cells will run about 1.3-1.4, but that will drop very quickly to 1.2-1.25v.

A Nicd cell will probably be damaged, if the voltage drops to below 1.0volt. Nicd's also, self recharge to a point, but not enough to power a device for a significant amount of time.

Asa for the memory effect, don't worry about it, as it does not exist the way it's commonly explained. A majority of "memory" problems come from either a overly-discharged cell (in which case it becomes damaged, and loses capacity) or an over-charged cell (which may cause the cell to vent, and also lose capacity).

Heat, age, and abuse are the major factors of Nicd failures.

--dan
 
I agree with Dano.

Also it is hard to measure the remaining charge in a nicad pack as the voltage changes very little as it is discharged. Untill the very end, and the the voltage drops fast. To prevent damage to the cells, you should recharge as soon as you notice a drop in preformance from your power tool.

Don't worry about memory effect, unless you are making a device that will discharge the cells to the Exact point over and over again, like a satilite or something.

Don't overcharge, don't over discharge, and you will get the most out of your pack.
 
okay, thanks for the memory explanation. You all explained it alot clearer than most manafactures do.. So, I just got a new bosch 18 volt cordless. The bat has two main termeinals and then two smaller ones. one is marked T which i assume is tempature and the other is marked c, I am not sure what that stands for. Do any of you? So sense this charger senses the bat temp it should help prolong the battery life. And If I am thinking right the charger senses the amount of charge and cuts off when charged.. So it is actually better to charge a nicad before you really notice a drop in power. Right? And I cant find a clear answer to this question. Is it best to store a nicad dead or full? I read it both ways.. so as long as i don't drain the nicad too far down and don't over work it these bats should last a while. I am beggining to see why my dewalt pack failed. No temp sensor and I am pretty sure it didn't monitor the voltage very good.

Thanks again for the help ful explanation.. Later Snapper
 
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