Section 8: Rechargeable battery measurements
Model 2450 Interactive SourceMeter® Instrument User's Manual
8-2
2450-900-01 Rev. A / June 2013
Figure 34: Battery charge-discharge cycle circuit diagram
1
Model 2450 is in source mode (V
S
> V
B
). Instrument functions as a
power supply; charge current (i) is positive.
2
Model 2450 is in sink mode (Vs > V
B
). Instrument functions as an
electronic load; discharge current (i) is negative.
Charging
A battery is usually charged using a constant current. This is accomplished using a Model 2450 as a
voltage source set to the voltage rating of the battery with the desired charging current set as the
current limit. At the start of the test, the battery voltage is less than the voltage output setting of the
Model 2450. As a result, this voltage difference drives a current which is immediately limited to the
user-defined current limit. When in current limit, the Model 2450 is acting as a constant current source
until it reaches the programmed voltage level. As the battery becomes fully charged, the current
decreases until it reaches zero or near zero. To prevent safety hazards or damage to the battery, be
careful not to overcharge the battery.
Discharging
When discharging a battery, the Model 2450 operates as a sink because it is dissipating power rather
than sourcing it. The voltage source of the Model 2450 is set to a lower level than the battery voltage.
The current limit sets the discharge rate. When the output is enabled, the current from the battery
flows into the HI terminal of the Model 2450. As a result, the current readings are negative. The
discharge current should stay constant until the battery voltage decreases to the voltage source
setting of the Model 2450.
