Question about Kepco Power Supply with Error Sensing

[Aaron William]

Hi, here are a few newb questions about error sensing -

I have a Kepco BOP 20-10M that I have connected to a solar cell. The purpose is to sweep voltage across the cell and create I-V curves.

Attached is a screenshot from the manual showing the setup for my application - using error sensing (4-wire Kelvin measurement). If I interpret the figure correctly, Kepco wants me to ground the load on the common side. My question is: Wouldn't all of the current from the output go to ground and not through the common wire? If this is the case, why have a common wire at all?

This wouldn't work for me because the manufacturer of this system put the ammeter (more accurately, a small resistor that sends a voltage signal to my A/D card) on the common side. I could put it on the output side but I never go against manufacturer wishes :)

Also, the solar cell has very little resistance when forward biased enough. I think I will just trip the breaker when the voltage sweep gets high enough because all the output current is going directly to ground with virtually no resistance.

Second question, the screenshot also shows placing a 1K resistor from output and common to their respective sense when relays are used. I do have two relays that connect, independently, the sense circuit and the current circuit to the load. Can someone explain the purpose of those resistors?

 

[Tom.G]

Can someone explain the purpose of those resistors?

The 1k resistors are to connect the Sense leads to the Power leads when the relay is open.

Without the resistors, when the relay is open the Sense leads see Zero volts. At this point the power supply goes to maximum output voltage trying to get a reading on the Sense wires. Not an ideal situation!

When the relay closes, the Sense leads are connected to the load (and supply output) and all is good.