8: Rechargeable battery measurements Model 2450 Interactive SourceMeter® Instrument
8-2 2450-900-01 Rev. C / December 2013
Figure 35: Battery charge-discharge cycle schematics
1
Model 2450 is in source mode (V
S
> V
B
). Instrument functions as a
power supply; charge current (i) is positive.
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. To do this, use 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 that is immediately limited to the user-defined
current limit. When in current limit, the Model 2450 acts 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.
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