Solar cell short circuit current using USB-6009

[senmurv76]

Hi All:

I am trying to conduct a very simple experiment to determine the effect of temperature on the open circuit voltage (Voc) and short circuit current (Isc) of a small size solar cell (max. 3V). I have a USB-6009 and NI 9211. I have no problem measuring Voc versus cell temperature: I connect the positive and negative terminals of the cell to the 6009's ai0 and GND terminals and log temperature using the 9211 -- all good.

Where I need help is determining how to measure Isc. If I were to use a digital multimeter I would directly connect it to the solar cell (without any additional series resistor), set my DMM to measure "current" and make measurements. However, I'm not sure how to do this with the 6009. Can the 6009 measure current if I were to directly connect the solar cell positive and negative terminals to the USB-6009's ai0 and GND terminals? Or do I need a series resistor? If I use a resistor would that not give me a current reading that is less than the actual Isc (i.e. Isc should be measured with no load attached to the solar cell)?

Any thoughts would appreciated!

[Henrik_Volkers]

Well, depending on the current range , how do you think your multimeter measure the current??

They use shunt resistors 🙂

For small currents you use a OPamp as an current to voltage converter. Here the OPamp has to provide/sink the same current than the DUT.

If you use a 0.05 Ohm resistor to measure 100mA you get a 5mV signal  . You can amplify it for your 6009 or (ab)use one of your TC channels as a low voltage reading device.

While you can get good OPamps for low money ( or just a click on the samples button), good resistors (stable and with low tempco, low thermoeletric) are harder to get.