There is no direct control of the sweep rate of the Daystar Tracers but the maximum sweep rate may be approximated if the configuration of the array to be tested is known.

The Daystar IV tracers use a capacitive load. This capacitance is initially pre-charged to approximately -24 V. When the PV array being tested is connected to the pre-charged capacitor using a transistor switch, the PV system goes from open-circuit voltage to -24 V in tens of micro-seconds. At this early stage, the PV system will be putting out whatever current it would at -24 V, typically near short-circuit current Isc. Immediately, the load capacitance in the DS-100 will start charging and the voltage will rise from -24 V to the open circuit voltage of the PV unit being tested. It's during this rise or sweep from short-circuit to open-circuit conditions that current and voltage data are collected for the IV curve.

As mentioned, the sweep rate depends on the interaction of the PV system and the capacitive load of the Daystar Tracer and follows the equation:

From this we can approximate the maximum sweep rate for voltage which occurs when the current is the highest (Isc). This sweep rate is nearly constant for much of the curve since PV systems typically have nearly constant current until the knee of the IV curve is reached. Once the current starts dropping, the rate of change of voltage will slow as well.

The Daystar DS-100C tracer has two capacitance values depending on the setting of the voltage range switch. For the high voltage range (600 V) the capacitance is approximately 1,500 uF (1.5E-3 F) and in the low voltage setting the capacitance is 5,000 uF (5E-3 F). The maximum sweep rate can be approximated by calculating Isc/Cap. However, most sweep rate values relate to a single PV cell so the calculated number must be adjusted for the number of series-paralel connected cells in the unit under test.

Please contact Daystar, Inc. with specific questions.