Tektronix Keithley SourceMeter 2450 User Manual page 80

Section 8: Rechargeable battery measurements
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2
Charging
A battery is usually charged using a constant current. To do this, use a 2450 as a voltage source set
to the voltage rating of the battery, with the target 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 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 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 2450 operates as a sink because it is dissipating power instead of
sourcing it. The voltage source of the 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 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 2450.
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Figure 41: Battery charge-discharge cycle schematics
2450 is in source mode (V
S
supply; charge current (i) is positive.
2450 is in sink mode (Vs < V
load; discharge current (i) is negative.
Model 2450 SourceMeter® Instrument User's Manual
> V ). Instrument functions as a power
B
). Instrument functions as an electronic
B
2450-900-01 Rev. E / August 2019