Ramsey Electronics DN1

DN1 • 5

oxidation reduction or “redox" chemical reaction in the cell, we effectively

decrease the chemically active surface area inside the cell. The lower this

surface area, the shorter the battery’s life. Since you don’t try to recharge

conventional batteries, you’ve never noticed this property until you started to

use rechargeable NiCad batteries.

To keep your cells working like new and to eliminate this memory effect, we’ve

built in an automatic discharge circuit that will properly discharge the cells

before their recharging.

So, you can see recharging a NiCad battery correctly can be a tricky business.

How can we charge the battery to its full potential, but not too much? The

answer is to watch the ∆V or change in voltage over time. As shown in the

graph, the battery voltage continues to rise while charging but drops slightly

when the cell is completely charged. By recognizing this point on the graph, a

charger can put just enough charge into the cell. By virtue of this voltage -vs-

time checking, it is also possible to charge the battery at a much higher

charging current - and significantly reduce the battery charging time. Once this

point is reached, it is best to “top off” the battery with a charge burst every now

and then.

Enter the Benchmarq BQ2003 NiCad battery charger IC. This cell monitoring /

charging IC performs all of the previously mentioned functions, and then some.

This smart IC is the “doctor” in our NiCad recharging unit.

TIME

VOLTAGE

Positive "Slope"

or + dV

Negative "Slope"

or - dV

Terminal Voltage

Time

for a NiCad Cell

Full Charge

Slope = Zero