Sunday, July 4, 2010

“high capacity” nickelcadmium (NiCd) batteries ...

Q I recently noticed some new “high capacity” nickelcadmium (NiCd) batteries in the RadioShack catalog and am trying to find more information about them. I downloaded the spec sheet for the AA size batteries (the only specs I could find) from the RadioShack Web site and it seems to confirm the capacity claim, but I wonder if there is some kind of hidden drawback. If these things really have twice the capacity of standard NiCds, I would think they would be showing up in more NiCd applications. Can you shed some light on these?

A For this answer the Doctor defers to internationally known battery expert Ken Stuart, W3VVN. “Yep, there are some ‘super cells’ out there, and they are about as good as the claims. So what gives? Just the usual situations. “First off, anyone can make a cell that has higher than usual capacity. How? Simple. Use a better separator between the plates, one which is more uniform in thickness, maybe a little tougher, and has undergone more quality control, and just happens to cost a little more as a result.

“Now, let’s do the same thing to the plates by making the thickness more uniform, so that everything packs better. Of course, this also adds to the cost of the cell. We also use a finer powder for the sintering process in making those plates, which increases the available reactive surface area. Finally, we can also use a more critical process for winding the plate-separator “sandwich” into a spiral slug and inserting this into the can. By doing all this, we now have a cell that has lots more ampere-hour capacity.

“Why don’t we see these cells in more applications? Pretend for a moment that you are a manufacturer of video cameras and you want to choose cells to use in your new product line. Do you want to spend the extra bucks for the high-capacity cells, thereby increasing the sale price of the unit? Or do you want to go with the cheapest cells you can find to keep the end cost of your SuperCam down to competitive levels? Remember, you’re in the business to manufacture and sell cameras, not batteries. And likewise, manufacturers of replacement battery packs know that the average Joe Customer usually wants the cheapest replacement he can get. In other words, it boils down to supply and demand. In this case the demand for super cells is light and so, consequently, is the supply.”

From QST September 1999