Ramsey Electronics DN1 manual Voltage, Time

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.

	Positive "Slope"	Full Charge
	or + dV dT	Slope = Zero
		Negative "Slope"
		or - dV dT
VOLTAGE	Terminal Voltage
	vs
	Time
	for a NiCad Cell
	TIME

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.

DN1 • 5