Sensing current in the array
I inserted a sensing resistor in the ground return loop of the array. I attempted to feed the RPi the signal using an adc(analog-to-digital-converter). What I hadn't anticipated is the shift in the ground reference.
By definition, ground is a zero point. Mathematicall, ground is 0volts. The charge controller feeds the battery bank and the inverter. The inverter 110VAC feeds the RPi through a 110VAC-to-5VDC converter/power supply. The RPi ground turns out to be 16+VDC above the RPi ground. I blew out an expander card, which I really didn't use, and the ADS1115 adc. I have several adc's and will use another one.
I spent some time considering solutions to the problem. I ordered a couple of AD620 instrumentation amplifiers with a maximum supply range of 18VDC. These will produce the difference between the ends of the sensing resistor which is typically around 0.5VDC. Until the AD620's arrive, I'm going to use a resistor network to attenuate the signal to a level compatible with the ADS1115, 6VDC maximum.
The resistors will be high impedence and have negligible effect on the signal. The signal will be reduced to 20% of the original, about 3.5VDC, That will be fed into a ADS1115 setup for differential input.
The solution may need system grounding. The panels may need to be grounding, especially since the house is wired conventionally with an earth ground. The charge controller has a positive ground and that makes matters a little less simple.
By definition, ground is a zero point. Mathematicall, ground is 0volts. The charge controller feeds the battery bank and the inverter. The inverter 110VAC feeds the RPi through a 110VAC-to-5VDC converter/power supply. The RPi ground turns out to be 16+VDC above the RPi ground. I blew out an expander card, which I really didn't use, and the ADS1115 adc. I have several adc's and will use another one.
I spent some time considering solutions to the problem. I ordered a couple of AD620 instrumentation amplifiers with a maximum supply range of 18VDC. These will produce the difference between the ends of the sensing resistor which is typically around 0.5VDC. Until the AD620's arrive, I'm going to use a resistor network to attenuate the signal to a level compatible with the ADS1115, 6VDC maximum.
The resistors will be high impedence and have negligible effect on the signal. The signal will be reduced to 20% of the original, about 3.5VDC, That will be fed into a ADS1115 setup for differential input.
The solution may need system grounding. The panels may need to be grounding, especially since the house is wired conventionally with an earth ground. The charge controller has a positive ground and that makes matters a little less simple.
posted by jimlynnjulian @ January 21, 2017
0 Comments
0 Comments:
Post a Comment
Subscribe to Post Comments [Atom]
<< Home