I have been working on this project off and on for 18 months and have decided to finally seek some help. The project goal is to accurately measure and record my power system performance parameters to a PC database.
My off grid power system consists of:
Trace SW4024 Inverter with internal 120A battery charger (I1)
80A MPPT PV charge controller (I2)
50A MPPT PV charge controller (I3)
Battery bank 24VDC 600AH
R1 is a 50mV 500A DC shunt
R2 and R3 are 100mV 200A DC shunt
Amp board: (see attached .PDF and .SCH)
U1 is a TI Quad OPA4277A opamp driven by a +15/0/-15 PS. U1(D) input shorted and not shown on drawing.
The box at the right (R10-13) represents the DATAQ DI-148U "single ended" +-10VDC ADC board inputs. USB output.
The circuit works fine on spice and on the bench. In the power shed (with real components), it's a totally different animal. I am seeing inconsistent voltage output swings at U1A when I3 increases. I am sure there are common mode, and ground loop issues in play.
This monitoring system worked consistently and accurately with I1, I2 connected, and R1 being the only shunt in the system. When I expanded the system to include I3, R2 & R3 the opamp output went crazy when I2 and I3 change.
in the real world, with a system such as this , can a single ended input ADC board even work. Will a differential input ADC solve all the problems. How do i improve/solve the grounding/common mode issues inherent with this low voltage system.
I have been lurking on this board for years and would like to thank you all for your unselfish contributions.
Ralph
My off grid power system consists of:
Trace SW4024 Inverter with internal 120A battery charger (I1)
80A MPPT PV charge controller (I2)
50A MPPT PV charge controller (I3)
Battery bank 24VDC 600AH
R1 is a 50mV 500A DC shunt
R2 and R3 are 100mV 200A DC shunt
Amp board: (see attached .PDF and .SCH)
U1 is a TI Quad OPA4277A opamp driven by a +15/0/-15 PS. U1(D) input shorted and not shown on drawing.
The box at the right (R10-13) represents the DATAQ DI-148U "single ended" +-10VDC ADC board inputs. USB output.
The circuit works fine on spice and on the bench. In the power shed (with real components), it's a totally different animal. I am seeing inconsistent voltage output swings at U1A when I3 increases. I am sure there are common mode, and ground loop issues in play.
This monitoring system worked consistently and accurately with I1, I2 connected, and R1 being the only shunt in the system. When I expanded the system to include I3, R2 & R3 the opamp output went crazy when I2 and I3 change.
in the real world, with a system such as this , can a single ended input ADC board even work. Will a differential input ADC solve all the problems. How do i improve/solve the grounding/common mode issues inherent with this low voltage system.
I have been lurking on this board for years and would like to thank you all for your unselfish contributions.
Ralph
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